RARE DISEASE
Congenital disorder of glycosylation
Congenital disorder of glycosylation
Congenital disorder of glycosylation
Synonyms: CDG, Carbohydrate deficient glycoprotein syndrome
Synonyms: CDG, Carbohydrate deficient glycoprotein syndrome
Synonyms: CDG, Carbohydrate deficient glycoprotein syndrome
Drug discovery
2
drugs
With orphan designations
Overview
Congenital Disorders of Glycosylation (CDG) are a genetically diverse group of over 130 inherited metabolic disorders caused by defects in protein and lipid glycosylation pathways. These multisystem conditions commonly present with developmental delay, hypotonia, failure to thrive, coagulopathy, and neurological abnormalities. Diagnosis relies on transferrin isoelectric focusing, glycan analysis, and genomic sequencing. While most subtypes lack curative treatments, targeted therapies (e.g., substrate/cofactor supplementation) exist for specific forms (e.g., MPI-CDG, PGM1-CDG) [1][4][5].
Therapies
Causative: Mannose (MPI-CDG), galactose (PGM1-CDG, SLC35A2-CDG), fucose (SLC35C1-CDG), and manganese (TMEM165-CDG) supplementation [3][5][6].
Symptomatic: Anticonvulsants, albumin infusions, and hormone replacement [5][15].
Emerging: Pharmacological chaperones (e.g., epalrestat) and gene therapy under investigation [3][12].
Categories: rare genetic diseases, rare inborn errors of metabolism
Research Papers
493 drug discovery papers about Congenital disorder of glycosylation, with 1 first-in-class and 14 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
493 drug discovery papers about Congenital disorder of glycosylation, with 1 first-in-class and 14 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
small molecules
2026-08-07 | Hypoglycosylation lowers the mechanical activation threshold of Piezo1 and enhances cortical neuronal mechanotransduction: implications for PMM2-CDG
Abstract Piezo1 is a mechanically activated cation channel whose N-linked glycans support protein maturation and plasma membrane trafficking, but their contribution to mechanical gating is unknown. We asked whether hypoglycosylation alters Piezo1 mechanosensitivity and cortical neuronal mechanotransduction, with potential relevance to neurological manifestations of congenital disorders of glycosylation (CDG). Human Piezo1 was studied in HEK293 cells after mutation of two conserved cap-domain N-glycosylation sites or inhibition of N-glycan maturation with swainsonine or kifunensine. Mechanically activated currents were recorded by cell-attached patch-clamp during incremental negative-pressure pulses, whereas Ca 2+ responses were measured during uniaxial stretch. Piezo1 abundance, synaptic localisation and stretch-evoked Ca 2+ signals were also examined in primary mouse cortical neurons. On poly-L-lysine, N2293Q or N2330Q shifted the pressure-response relationship towards lower activating pressures without changing maximal current or inactivation kinetics. This effect was absent on collagen. Swainsonine and kifunensine reduced mature Piezo1 glycosylation and lowered the mechanical activation threshold. Hypoglycosylation enhanced Ca 2+ entry during submaximal stretch in HEK293 cells. In cortical neurons, inhibition of glycan maturation increased somatic Piezo1 immunoreactivity without changing its association with synaptic markers, and potentiated Ca 2+ responses to both the Piezo1 activator Yoda1 and submaximal stretch. Thus, mature N-glycans and the extracellular adhesive environment jointly set Piezo1’s mechanical activation threshold rather than merely regulating biosynthesis and trafficking. These findings establish glycosylation-mechanics coupling as a determinant of neuronal force sensing and suggest that, by facilitating Piezo1 recruitment, defective glycosylation may increase cortical vulnerability to mechanical stress, potentially contributing to head trauma-triggered neurological episodes in phosphomannomutase 2 deficiency (PMM2-CDG). Key points Piezo1 channels convert mechanical forces into electrical and calcium signals. N-linked glycans support channel trafficking to the plasma membrane, but whether they tune the force needed for Piezo1 activation was unknown. Mutating either of two conserved N-glycosylation sites in Piezo1 cap domain, or pharmacologically restricting N-glycan maturation, lowered channel’s mechanical activation threshold without changing maximal current or inactivation. This sensitisation depended on the adhesive substrate (occurred on poly-L-lysine but not collagen), and was most evident during submaximal stretch, showing that glycosylation and the extracellular mechanical environment jointly determine Piezo1 force sensing. In mouse cortical neurons, impaired N-glycan maturation increased somatic Piezo1 abundance and enhanced Ca 2+ responses to its chemical activator Yoda1 and stretch, without changing synaptic localisation. By allowing weak mechanical inputs to recruit Piezo1 more effectively, defective glycosylation may increase cortical responses to mechanical stress and help explain susceptibility to head trauma-triggered neurological episodes in phosphomannomutase 2 deficiency (PMM2-CDG).
2026-07-29 | Repurposing the HMG-CoA reductase inhibitor atorvastatin for SRD5A3-congenital disorder of glycosylation
Abstract Background Steroid 5 alpha-reductase 3-related congenital disorder of glycosylation (SRD5A3-CDG) is a rare inherited disease characterized by neurological dysfunction, including ataxia, as well as developmental and visual impairments, with no approved treatments. The disease is caused by defects in dolichol biosynthesis, a pathway essential for protein glycosylation. However, the lack of suitable in vivo models has limited both mechanistic insight and therapeutic development. Methods We generated a Caenorhabditis elegans model carrying a patient-relevant loss-of-function mutation and performed a motility-based phenotypic drug repurposing screen to identify compounds that improve disease-relevant phenotypes. Lead compounds were evaluated in behavioral, neuronal, and metabolomic assays in worms and in fibroblasts from four individuals with SRD5A3-CDG. Results Here we show that SRD5A3-deficient worms exhibit developmental delay, neuronal dysfunction, and metabolic alterations consistent with dysregulation of the mevalonate pathway. The screen identifies multiple classes of compounds that improve motility, including the cholesterol-lowering drug atorvastatin. Atorvastatin improves multiple disease-relevant phenotypes in the worm model. In patient-derived fibroblasts, treatment partially restores the balance between polyprenol and dolichol, which is disrupted in SRD5A3-CDG. Conclusions These findings establish an in vivo model of SRD5A3-CDG and identify modulation of the mevalonate pathway as a potential therapeutic strategy. The results support further investigation of atorvastatin as a repurposed treatment and demonstrate an approach for combining model organism screening with human cell validation to accelerate rare disease drug discovery.
2026-07-10 | B4GALT5 deficiency impairs glycosphingolipid biosynthesis: a new Congenital Disorder of Glycosylation?
Lactosylceramide is a glycosphingolipid precursor synthesized by two dedicated galactosyltransferases, B4GALT5 and B4GALT6. The specific roles of B4GALT5 and B4GALT6 in humans have not yet been clearly defined. Here, we report the first human case with bi-allelic loss-of-function variants in B4GALT5, suggesting that intact B4GALT5 activity is indispensable for normal glycosphingolipid biosynthesis and human development. We identified bi-allelic variants in the B4GALT5 gene in a child presenting with microcephaly, mild cognitive impairment, and bilateral cataracts. B4GALT5/6 double KO cells transfected with B4GALT5 carrying either of the variants identified in the patient lacked lactosylceramide synthase activity and failed to produce glycosphingolipids. In-silico analyses predicted decreased protein stability and impaired UDP-Gal binding for both B4GALT5 variants. Together, these findings indicate that both variants result in deficient B4GALT5 activity, leaving B4GALT6 as the sole source of lactosylceramide synthase activity. Consistent with this, patient plasma and fibroblasts exhibited an approximately 80% reduction in glycosphingolipid levels compared with healthy controls. Unexpectedly, when expressed in model cells human B4GALT6 displayed lower expression and lower catalytic activity, than human B4GALT5, raising questions about its capacity to compensate for B4GALT5 deficiency. In conclusion, we identified a potential new congenital disorder of glycosylation caused by deficient lactosylceramide synthase activity that may be insufficient to support glycosphingolipids synthesis at levels required for normal brain function.
2026-06-30 | Management of pregnancy and outcomes in a woman with mannose-6-phosphate isomerase deficiency (MPI-CDG).
Congenital Disorder of Glycosylation type Ib (MPI-CDG) is a rare autosomal recessive metabolic disorder caused by deficiency of mannose-6-phosphate isomerase, resulting in impaired N-glycosylation. Unlike other CDG subtypes, MPI-CDG is not associated with neurodevelopmental impairment and is effectively treated with oral D-mannose supplementation. However, evidence guiding management during pregnancy is scarce, and D-mannose is generally avoided due to limited safety data. We describe the long-term course and pregnancy outcomes of a woman diagnosed with MPI-CDG in infancy. She was treated with oral D-mannose throughout childhood with good clinical response but demonstrated intermittent non-compliance in adulthood, complicated by hepatic fibrosis, protein-losing enteropathy, osteoporosis, anaemia, and musculoskeletal manifestations. She had two pregnancies without D-mannose supplementation. The first pregnancy was complicated by microcytic anaemia, hypoalbuminemia, pregnancy-induced cholestasis, and emergency caesarean section. A male infant was delivered and later diagnosed with Hirschsprung disease, requiring surgical correction with good outcome. Postpartum assessment of the mother demonstrated progression of liver disease to cirrhosis (F4). The second pregnancy proceeded with fewer complications and resulted in emergency caesarean delivery of a healthy female infant with normal postnatal glucose control and growth. This case contributes to the limited literature on pregnancy in MPI-CDG and illustrates that successful pregnancies are possible despite advanced multisystem disease and cessation of D-mannose therapy. It highlights the importance of multidisciplinary care, close hepatic and nutritional monitoring, and the need for further studies to clarify the safety and role of D-mannose supplementation during pregnancy.
2026-06-11 | Recurrent hemophagocytic lymphohistiocytosis in COG deficiency: a case series and systematic review of inflammatory manifestations.
Conserved oligomeric Golgi (COG) deficiencies are rare congenital disorders of glycosylation characterized by severe multisystem involvement. Recurrent inflammatory episodes have been reported but remain poorly understood and are likely underrecognized. We describe three patients with COG6 or COG7 deficiency presenting recurrent episodes of hemophagocytic lymphohistiocytosis (HLH). In parallel, we conducted a systematic review of the literature to assess the frequency and characteristics of inflammatory manifestations in COG deficiency. All three patients experienced recurrent febrile episodes associated with biological features of HLH. In two cases, these episodes were followed by neurological deterioration and onset of epilepsy. Early or prophylactic corticosteroid therapy during febrile episodes appeared to mitigate both the severity and neurological impact of inflammatory flares. The literature review identified recurrent, unexplained, and poorly tolerated febrile episodes in approximately 40% of reported patients. Only one additional case of fully documented HLH was identified. However, multiple reports described partial or suggestive HLH features, supporting the hypothesis that hyperinflammatory manifestations are underdiagnosed in this population. COG deficiencies, especially COG6 and COG7, may be complicated by recurrent and potentially severe hyperinflammatory episodes, including HLH, with significant neurological consequences. These findings suggest a link between glycosylation defects and immune dysregulation. Early recognition and preventive anti-inflammatory strategies are recommended.
gene therapies
2026-01-01 | Modeling human PMM2-CDG in medaka to understand systemic effects of hypoglycosylation on development
Congenital disorders of glycosylation (CDG) are a group of rare metabolic diseases caused by mutations in the enzymes involved in glycosylation. To date, no conclusive pathogenic mechanism is linked to the disease and there are only limited therapeutic options available. The most common form of CDG is caused by compound heterozygous hypomorphic alleles of the cytosolic enzyme Phosphomannomutase 2 (PMM2), leading to global protein hypoglycosylation and a multiorgan phenotype in patients. Complete loss-of-function mutations in the essential protein are incompatible with life. Patients that survive carry mutations that lead to reduced enzyme activity of PMM2. PMM2 plays a crucial role at the basis of the glycosylation cascade in the endoplasmic reticulum by providing the essential mannose precursor required for the three glycosylation routes N-glycosylation, O- and C-mannosylation. The entire glycosylation machinery is evolutionarily highly conserved which allows generating translational models in other organisms. The small teleost medaka (Oryzias latipes) offers a great advantage as model organism to investigate the early embryogenesis through the extrauterine and transparent developing embryos. To understand acute effects of Pmm2 loss on development and disease progression, I have created translational models that mimic the reduced residual enzyme activity of PMM2-CDG patients. I followed two routes to investigate the role of PMM2 on development: establish a conditional knockdown system for acute Pmm2 interference at the protein level and patient-based genetic models by precision genome editing in medaka. For the conditional knockdown in medaka, I applied an inducible degron system to selectively degrade Pmm2-GFP, mimicking reduced enzyme activity. To generate patient-based pmm2 alleles, I used canonical base editing to generate the p.C139R mutation and a deletion variant. Further, I developed and carefully examined a novel two step one-shot base editing approach termed “inception”. Inception introduces a new binding site for a second base editing event that subsequently leads to the anticipated edit. With inception I created one of the common patient mutations p.F119L. Depending on the generated alleles, different pmm2 variants resulted in varying enzymatic activity in medaka, phenocopied the patient symptoms and caused hypoglycosylation of proteins. Bottom-up proteomics revealed molecular changes already present before the onset of multisystemic phenotypes, affecting particularly mRNA processing and eye development.
2025-11-03 | AAV9-mediated NGLY1 gene replacement suppresses non-epileptic convulsions in Ngly1-/- rats.
N-glycanase 1 (NGLY1) deficiency is a rare autosomal-recessive neurological disorder characterized by neurological dysfunction and so far, has no effective therapy. A systemic Ngly1-/- rat model recapitulates many patient symptoms, including developmental delay, motor and cognitive deficits. Here we carried out further detailed phenotypic analyses for the Ngly1-/- rats, with particular focus on those easily translatable to patients' symptoms, i.e. sleep disturbances, EEG abnormalities and convulsive behaviors. EEG/EMG recordings revealed fragmented sleep and frequent spontaneous epileptiform discharges in Ngly1-/- rats. Continuous video-EEG monitoring confirmed a high incidence of convulsive events with/without epileptic discharge. At three weeks of age, Ngly1-/- rats received a single intracerebroventricular injection of AAV9-hNGLY1. We then examined whether central nervous system-targeted gene therapy using an adeno-associated virus serotype 9 carrying human NGLY1 (AAV9-hNGLY1) can rescue those phenotypes. While NGLY1 protein was robustly expressed in the brain with partial restoration of enzymatic deglycosylation activity, AAV9-hNGLY1-treated Ngly1-/- rats showed no significant improvement in EEG abnormalities or sleep disruption. In sharp contrast, AAV9-hNGLY1 significantly reduced the frequency of non-epileptic convulsive episodes. These findings expand the phenotypic characterization of the Ngly1-/- rat model to include sleep and seizure phenotypes and demonstrate that AAV9-mediated NGLY1 restoration can suppress overt motor convulsions. On the other hand, persistent EEG seizures and sleep disturbances indicate only a partial therapeutic benefit, underscoring the need for further refinement of gene therapy strategies, as well as additional therapeutic options, for NGLY1 deficiency.
2025-08-20 | AAV-based gene replacement reverses Neurexin-2 downregulation in the cerebellum of a mouse model of phosphomannomutase 2 deficiency (PMM2-CDG).
Phosphomannomutase 2 (PMM2) deficiency is the most common congenital disorders of glycosylation (CDG) with an estimated incidence ranging from 1:20,000 to 1:80,000. Patients manifest a broad spectrum of clinical manifestations, with neurological deficits often emerging as the earliest sign, and may progress to severe multi-organ dysfunction. Mortality reaches 20% by the age of six, primarily due to severe infections, liver insufficiency, or cardiomyopathy. The pathophysiology of the tissue-specific complications remains unclear and there is currently no cure for the disease. In this study, we performed omics analyses of cerebella isolated from a mouse model of PMM2-CDG. RNA-Seq analysis revealed altered gene expression in pathways involved in immune responses and coagulation, while proteomic analysis of proteins enriched by lectin-affinity chromatography identified proteins required for neurodevelopment and neurotransmission. We validated our results by demonstrating significant downregulation of Neurexin-2 in the Pmm2 knockout (KO) mouse cerebella and showed that its reduced abundance can be reversed by AAV9- PMM2 gene treatment of the Pmm2 KO mice.
2025-08-14 | Are viral vector-mediated therapies compatible with aberrant glycosylation?
The ability of adeno-associated viruses (AAVs) to transduce host cells relies on interactions with glycan moieties on the cellular surface. Consequently, disrupted protein glycosylation, which is seen in a range of neurodevelopmental and neurodegenerative diseases, could impair transduction efficiency. Understanding how altered glycosylation impacts AAV binding is essential to optimize AAV-mediated therapeutic strategies. We used glycoproteomics data from cortical brain organoids and iCardiomyocytes of individuals with congenital disorders of glycosylation (CDG) (ALG13-, PMM2-, and PGM1-CDG) to examine the abundance of AAV-binding glycan species. Additionally, we assessed the abundance of coreceptors in proteomics data. We found that the abundance of AAV-binding glycan species was downregulated for all CDG subtypes, but this was significant only for AAV5-, AAV8-, and AAV9-binding glycan motifs in PGM1-CDG. The proteomics data showed significantly decreased abundance of the coreceptor PDGFRβ in ALG13-CDG. The downregulation of glycan species and AAV coreceptors in models of aberrant protein glycosylation underscores the need to optimize AAV selection for conditions with altered protein glycosylation, including CDG and neurodegenerative diseases such as Parkinson's and Alzheimer's disease.
2025-03-18 | AAV-based gene replacement therapy prevents and halts manifestation of abnormal neurological phenotypes in a novel mouse model of PMM2-CDG.
Inherited Phosphomannomutase 2 (PMM2) deficiency, also known as PMM2-CDG, is the most prevalent N-linked congenital disorder of glycosylation (CDG), occurring in approximately 1 in 20,000 individuals in certain populations. Patients exhibit a spectrum of symptoms, with neurological involvement being a prominent feature, often manifesting as the initial clinical sign, and can range from isolated neurological deficits to severe multi-organ dysfunction. Given the absence of curative treatments and a high mortality rate before the age of two, alongside considerable lifelong morbidity, there is an urgent need for innovative therapeutic approaches. To address this unmet need, we developed a tamoxifen-inducible Pmm2 knockout (KO) mouse model with widespread tissue deficiency of Pmm2 expression. Characterization of the mouse model to-date revealed distinct neurological phenotypes relevant to PMM2-CDG, as assessed by the Composite Phenotype Scoring System and Open Field Test. Notably, PMM2 augmentation through AAV9-PMM2 gene replacement therapy prevented and halted the disease-relevant neurological phenotypes induced by Pmm2 KO in the animals. These findings underscored the promise of AAV9-PMM2 gene replacement in managing PMM2-CDG.
proteins
2026-07-07 | Structural insights into mutated human phosphoglucomutase 1 (PGM1) using computational approaches
The phosphoglucomutase 1 (PGM1) enzyme plays a critical role in metabolism and glycosylation in the human body. PGM1 has been linked to multiple disease phenotypes, including the inherited metabolic disorder known as congenital disorders of glycosylation (CDGs). Numerous clinical studies have shown that mutations in key regions of the PGM1 gene affect catalytic activity and induce folding defects of the enzyme. To delve into molecular changes at the supramolecular level, the structural, stability, and other features of PGM1 variants (T19A, N38Y, and D62H) were studied in the present work. To this end, molecular dynamics (MD) simulation at a long timescale (500 ns) was carried out. Parameters such as root-mean-square deviation (RMSD), root-mean-square fluctuations (RMSF), radius of gyration (Rg), solvent-accessible surface area (SASA), hydrogen bonds, and free energy landscape (FEL) were studied and compared with those of the wild-type PGM1. It was noted that mutations 19 A, N38Y, and D62H significantly alter the protein’s structural behavior, causing increased flexibility, reduced stability, and compactness.
2026-07-02 | Effects of Deficient Glycosylation and Deglycosylation on Sperm Condition in Zebrafish ( Danio rerio )
Abstract Congenital disorders of glycosylation and deglycosylation are rare, serious, and lethal disorders afflicting humans. CDGs and CDDGs result in loss of function enzymes which fail to build or break down oligosaccharides on proteins. This can produce protein aggregates and, in turn, reactive oxygen species that harm the cell eventually leading to autophagy and apoptosis. Because sperm contain high concentrations of polyunsaturated fatty acids, they are especially sensitive to these effects, which is understood as one of the leading factors in human male infertility. Sperm are developed in zebrafish similarly to humans and are useful models to examine human reproductive health, as well as genetic disorders. The combination of these advantages makes the analysis of sperm from zebrafish with heterozygous ALG1 or DPAGT1 CDGs or the NGLY1 CDDG suitable. Analysis of sperm concentration, motility, status, viability, and hypoosmotic swelling demonstrated the effects of these disorders on sperm quality. Results showed a significant decrease in sperm concentration, motility, and hypoosmotic swelling for all mutant zebrafish compared to the wild type. This suggests that CDGs and CDDGs influence the amount of sperm produced, the percentage of sperm cells that are mobile, and the integrity of the plasma membrane.
2026-06-01 | Resistant Epilepsy and Developmental Delay in a Syndromic Infant: A Case of Congenital Disorder of Glycosylation Type Ik From India.
Type I congenital disorder of glycosylation (CDG) is a group of genetic disorders that affect the biosynthesis of dolichol-linked oligosaccharides or the transfer of oligosaccharides onto nascent glycoproteins. Mutations in the ALG1 gene cause CDG type Ik. We report a ten-month-old female with CDG type Ik presenting with recurrent seizures, global developmental delay, hypotonia, and dysmorphic features. Whole-exome sequencing revealed a homozygous likely pathogenic variant chr16:5071980G>T or c.131G>T or p.Gly44Val in the ALG1 gene. Transferrin isoform analysis showed a CDG type I pattern, consistent with a glycosylation disorder. This case emphasizes the importance of early clinical suspicion, metabolic screening, and genetic testing in infants with unexplained recurrent seizures, syndromic features, and multisystemic involvement.
2026-05-27 | The revised three-step detour pathway in dolichol biosynthesis is evolutionarily conserved in budding yeast.
The identification of SRD5A3, a causative gene for congenital disorders of glycosylation (CDGs), together with its yeast ortholog DFG10, established the prevailing model that dolichol is synthesized from polyprenol in a single step. Subsequently, a recent discovery of DHRSX in CDG patients revised this view and led to the proposal of a three-step detour pathway for dolichol biosynthesis. However, it remains unclear whether this pathway represents a conserved mechanism or reflects evolutionary diversity in eukaryotes. Here, we identified TDA5 as a yeast ortholog of DHRSX. Deletion of TDA5 caused glycosylation defects, reduced dolichol levels, and accumulated polyprenol. All these phenotypes were rescued by expression of DHRSX, but not by DFG10 or SRD5A3. These findings show that Tda5 serves the same function as DHRSX in yeast, thereby demonstrating conservation of the three-step detour pathway in yeast and supporting a broader eukaryotic framework for dolichol biosynthesis.
2026-05-01 | The role of GMDS mutation in fucosylation disease pathogenesis and hair cell regeneration in zebrafish
Fucosylation is an essential cellular process involved in development, organ maintenance, and tissue repair. Defective fucosylation has been implicated in several human diseases, including early-onset and adult late-onset complex diseases. This work has investigated the role of the GDP-mannose 4,6-dehydratase (GMDS) enzyme gene, required for the rate-limiting reaction for GDP-fucose synthesis, in congenital disorders of glycosylation (CDGs), glaucoma pathogenesis, and hair cell regeneration for hearing loss therapeutic development using zebrafish (Danio rerio). Using molecular, genetic, histological, and imaging techniques, this project has successfully modeled clinical features of CDG patients due to defective fucosylation. Zebrafish gmds⁻ᐟ⁻ mutants (gmdsⁿᶠˡ²) at two days post fertilization (dpf) significantly replicated major clinical features of CDGs reported in patients, such as seizure, epilepsy, and defective neuronal coordination. In addition, this work reveals defective Crystallin protein stress response as the main mechanism of GMDS’s role in glaucoma development risk and confirms an earlier genome wide association studies (GWAS)’s findings, which found GMDS single nucleotide polymorphisms (SNPs) associated with glaucoma pathogenesis and treatment resistance. Furthermore, the zebrafish gmds⁻ᐟ⁻ mutant used in this study also showed increased capacity to regenerate lateral line neuromast hair cells after neomycin ablation. Zebrafish hair cells share similarity in function and structure to the human inner ear hair cells and share about 76% homologous genes of the human genome, thus making translation to human treatment for hearing loss possible. Overall, these findings establish GMDS as a central regulator of fucosylation-dependent signalling pathways in the eye retina stress response activation, hair cell regeneration, and pathology of congenital disorders of glycosylation due to defective fucosylation.
cell therapies
2026-01-16 | PMM2-CDG and the Role of Liver Transplantation as a Long-Term Solution: A Case Report.
Phosphomannomutase-2 congenital disorder of glycosylation (PMM2-CDG) is the most common congenital disorder of glycosylation, affecting protein glycosylation across multiple organ systems. Hepatic involvement may range from isolated elevations in liver transaminases to end-stage liver disease. Reported outcomes of liver transplantation as a treatment modality are sparse. We describe one of the first reported cases of liver transplantation in a child with PMM2-CDG and interim post-transplant outcomes. This patient was diagnosed at 4 months of age after presenting with failure to thrive, lipodystrophy, hypotonia, developmental delay, elevated transaminases, hypoalbuminemia, and coagulopathy. He developed cirrhosis and portal hypertension as well as sequelae of poor protein glycosylation. All these included coagulopathy, protein-losing enteropathy, and refractory ascites requiring serial intravenous fresh frozen plasma and furosemide. He ultimately underwent a liver transplant, after which his ascites resolved. Post-transplant, he developed new-onset recurrent pericardial effusions, suspected to be from a viral etiology versus extrahepatic manifestations of PMM2-CDG, and elevated transaminases following transplantation. Liver transplantation may offer clinical benefit in PMM2-CDG with severe hepatic involvement, including resolution of ascites and improved quality of life, due to its potential to restore liver glycosylation function. However, this is only a partial correction as persistent extrahepatic manifestations underscore the need for further research into transplant outcomes and systemic disease progression in CDG.
2025-04-25 | Clinical Manifestations of Phosphoglucomutase 3 (PGM3) Deficiency
Background and Aims Phosphoglucomutase 3 (PGM3) deficiency is a congenital disorder of glycosylation characterized by elevated IgE, atopy, recurrent infections, autoimmunity, cognitive impairment, and cytopenias. As more patients have been described, the variability in clinical presentation has become apparent. We aimed to further characterize the phenotype of PGM3 deficiency at our center. Methods Medical records were retrospectively reviewed for 10 patients from 4 families with PGM3 deficiency seen at the NIH Clinical Center. Results Ten patients (7 males and 3 females), aged 5 to 38 years, were evaluated at our center. Atopy was the most common manifestation, with eczema seen in all 10 patients and food and drug allergies in 9 and 8 patients, retrospectively. Sinopulmonary infections were noted in 8 patients, complicated by bronchiectasis in 5, and 5 had viral mucocutaneous infections. Seven patients had varying levels of neurocognitive impairment. Five patients had autoimmunity, including vasculitis in 4, glomerulonephritis in two, and psoriasis in one. Three affected siblings had malignancy: two with EBV-positive Hodgkin’s lymphoma, two with EBV-positive diffuse large B cell lymphoma (including one with prior Hodgkin’s), and one with squamous cell CA (SCC). Additional findings included bony abnormalities in 8 (6 with scoliosis, 2 with endplate abnormalities), single kidney (1), and heart failure (1). Nine patients had lymphopenia, 7 had severe chronic neutropenia (ANC < 500), and one had hemolytic anemia. Bone marrow biopsies were evaluated for 7 patients; three were normocellular despite neutropenia, one was hypocellular with no dysplastic features, and one had erythroid hypercellularity due to chronic hemolysis. One patient is alive and well after hematopoietic cell transplantation (HCT), with resolution of recurrent infections, severe neutropenia, and atopic dermatitis, and one patient had a lung transplant for severe bronchiectasis. There were 3 fatalities between ages 36 and 42 from malignancy (2 with lymphoma and one SCC) and one COVID-related fatality at age 18. Conclusions Although this is a multi-systemic disorder, the 30% mortality in early adulthood due to virally driven malignancies along with severe infection and chronic neutropenia suggests that HCT should be strongly considered.
2024-08-04 | HepG2 PMM2-CDG knockout model: A versatile platform for variant and therapeutic evaluation.
Phosphomannomutase 2 deficiency (PMM2-CDG), the most frequent congenital disorder of glycosylation, is an autosomal recessive disease caused by biallelic pathogenic variants in the PMM2 gene. There is no cure for this multisystemic syndrome. Some of the therapeutic approaches that are currently in development include mannose-1-phosphate replacement therapy, drug repurposing, and the use of small chemical molecules to correct folding defects. Preclinical models are needed to evaluate the efficacy of treatments to overcome the high lethality of the available animal model. In addition, the number of variants with unknown significance is increasing in clinical settings. This study presents the generation of a cellular disease model by knocking out the PMM2 gene in the hepatoma HepG2 cell line using CRISPR-Cas9 gene editing. The HepG2 knockout model accurately replicates the PMM2-CDG phenotype, exhibiting a complete absence of PMM2 protein and mRNA, a 90% decrease in PMM enzymatic activity, and altered ICAM-1, LAMP1 and A1AT glycoprotein patterns. The evaluation of PMM2 disease-causing variants validates the model's utility for studying new PMM2 clinical variants, providing insights for diagnosis and potentially for evaluating therapies. A CRISPR-Cas9-generated HepG2 knockout model accurately recapitulates the PMM2-CDG phenotype, providing a valuable tool for assessing disease-causing variants and advancing therapeutic strategies.
2023-10-23 | MAGT1 deficiency in XMEN disease is associated with severe platelet dysfunction and impaired platelet glycoprotein N-glycosylation.
X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection, and neoplasia (XMEN) disease is a primary immunodeficiency due to loss-of-function mutations in the gene encoding for magnesium transporter 1 (MAGT1). Furthermore, as MAGT1 is involved in the N-glycosylation process, XMEN disease is classified as a congenital disorder of glycosylation. Although XMEN-associated immunodeficiency is well described, the mechanisms underlying platelet dysfunction and those responsible for life-threatening bleeding events have never been investigated. To assess platelet functions in patients with XMEN disease. Two unrelated young boys, including one before and after hematopoietic stem cell transplantation, were investigated for their platelet functions, glycoprotein expression, and serum and platelet-derived N-glycans. Platelet analysis highlighted abnormal elongated cells and unusual barbell-shaped proplatelets. Platelet aggregation, integrin αIIbβ3 activation, calcium mobilization, and protein kinase C activity were impaired between both patients. Strikingly, platelet responses to protease-activated receptor 1 activating peptide were absent at both low and high concentrations. These defects were also associated with decreased molecular weights of glycoprotein Ibα, glycoprotein VI, and integrin αIIb due to partial impairment of N-glycosylation. All these defects were corrected after hematopoietic stem cell transplantation. Our results highlight prominent platelet dysfunction related to MAGT1 deficiency and defective N-glycosylation in several platelet proteins that could explain the hemorrhages reported in patients with XMEN disease.
2023-06-23 | Homozygous truncating variant in MAN2A2 causes a novel congenital disorder of glycosylation with neurological involvement.
Enzymes of the Golgi implicated in N-glycan processing are critical for brain development, and defects in many are defined as congenital disorders of glycosylation (CDG). Involvement of the Golgi mannosidase, MAN2A2 has not been identified previously as causing glycosylation defects. Exome sequencing of affected individuals was performed with Sanger sequencing of the MAN2A2 transcript to confirm the variant. N-glycans were analysed in patient-derived lymphoblasts to determine the functional effects of the variant. A cell-based complementation assay was designed to assess the pathogenicity of identified variants using MAN2A1/MAN2A2 double knock out HEK293 cell lines. We identified a multiplex consanguineous family with a homozygous truncating variant p.Val1101Ter in MAN2A2. Lymphoblasts from two affected brothers carrying the same truncating variant showed decreases in complex N-glycans and accumulation of hybrid N-glycans. On testing of this variant in the developed complementation assay, we see the complete lack of complex N-glycans. Our findings show that pathogenic variants in MAN2A2 cause a novel autosomal recessive CDG with neurological involvement and facial dysmorphism. Here, we also present the development of a cell-based complementation assay to assess the pathogenicity of MAN2A2 variants, which can also be extended to MAN2A1 variants for future diagnosis.
other
2025-09-18 | Table 3_Immunopathology in PMM2-CDG: Defective glycosylation impact in the TNFα -TNFR1 signalling pathway.xlsx
Introduction Glycosylation is a post-translational modification that plays a crucial role in immune system activity. Phosphomannomutase 2-Congenital Disorder of Glycosylation (PMM2-CDG) is a rare genetic disease affecting glycosylation with a multi-systemic impact. PMM2-CDG patients commonly show immune disfunction and elevated pro-inflammatory cytokine levels that may link to other symptoms. However, the underlying immune mechanisms remain unclear. Given Tumour Necrosis Factor (TNF)’s key role in inflammation, this study proposes that defective glycosylation of its receptors disrupts intracellular signalling, leading to changes in the immune response of PMM2-CDG patients. Methods To address this, we applied an integrative approach, combining transcriptomics, glycomics, and immune-related assays to investigate the impact of TNF-a stimulation via TNF receptor 1 (TNFR1) in a cohort of PMM2-CDG patients’ skin fibroblasts. Results Our results reveal a multifaceted disruption of TNF-a signalling in PMM2-CDG fibroblasts. We observed structural abnormalities in TNFR1, including altered receptor shedding. PMM2-CDG cells also showed an altered N-glycosylation profile, affecting particularly, high mannose N-glycans. At transcriptional level, PMM2-CDG cells, especially those bearing the R141H heterozygous variant, exhibited a distinct gene expression profile, after stimulation, characterized by dysregulation of immune and signalling pathways. Functionally, these molecular alterations translated into a diminished secretion of key inflammation and infection mediators, such as interleukin-6 (IL-6) and C-C Motif chemokine ligand 5 (CCL5) upon TNF-a stimulation. Similarly, essential signalling kinases including extracellular-signal-regulated kinase (ERK) 1/2, p38 and c-Jun N- terminal kinase (JNK) 2 showed reduced expression in PMM2-CDG cells, and their expression did not alter following TNF-a stimulation, unlike control cells. Conslusion Our findings point to TNFR1 signalling dysregulation as a key contributor to immune dysfunction in PMM2-CDG. Importantly, our study identifies TNFR1 as a promising therapeutic target, suggesting that strategies aimed at modulating TNFR1 activity or restoring glycosylation homeostasis could provide new approaches for treatment development. This work advances our understanding of PMM2 -CDG immunopathology and opens opportunities for targeted therapeutics.
2023-06-02 | A liposomal carbohydrate vaccine, adjuvanted with an NKT cell agonist, induces rapid and enhanced immune responses and antibody class switching
Congenital disorders of glycosylation (CDGs) are genetic diseases caused by gene defects in glycan biosynthesis pathways, and there is an increasing number of patients diagnosed with CDGs. Because CDGs show many different clinical symptoms, their accurate clinical diagnosis is challenging. Recently, we have shown that liposome nanoparticles bearing the ALG1-CDG and PMM2-CDG biomarkers (a tetrasaccharide: Neu5Ac-α2,6-Gal-β1,4-GlcNAc-β1,4-GlcNAc) stimulate a moderate immune response, while the generated antibodies show relatively weak affinity maturation. Thus, mature antibodies with class switching to IgG are desired to develop high-affinity antibodies that may be applied in medical applications.In the present study, a liposome-based vaccine platform carrying a chemoenzymatic synthesized phytanyl-linked tetrasaccharide biomarker was optimized. The liposome nanoparticles were constructed by dioleoylphosphatidylcholine (DOPC) to improve the stability and immunogenicity of the vaccine, and adjuvanted with the NKT cell agonist PBS57 to generate high level of IgG antibodies. The results indicated that the reformulated liposomal vaccine stimulated a stronger immune response, and PBS57 successfully induce an antibody class switch to IgG. Further analyses of IgG antibodies elicited by liposome vaccines suggested their specific binding to tetrasaccharide biomarkers, which were mainly IgG2b isotypes.Immunization with a liposome vaccine carrying a carbohydrate antigen and PBS57 stimulates high titers of CDG biomarker-specific IgG antibodies, thereby showing great potential as a platform to develop rapid diagnostic methods for ALG1-CDG and PMM2-CDG.
2023-05-24 | Germline C1GALT1C1 mutation causes a multisystem chaperonopathy.
Mutations in genes encoding molecular chaperones can lead to chaperonopathies, but none have so far been identified causing congenital disorders of glycosylation. Here we identified two maternal half-brothers with a novel chaperonopathy, causing impaired protein O-glycosylation. The patients have a decreased activity of T-synthase (C1GALT1), an enzyme that exclusively synthesizes the T-antigen, a ubiquitous O-glycan core structure and precursor for all extended O-glycans. The T-synthase function is dependent on its specific molecular chaperone Cosmc, which is encoded by X-chromosomal C1GALT1C1. Both patients carry the hemizygous variant c.59C>A (p.Ala20Asp; A20D-Cosmc) in C1GALT1C1. They exhibit developmental delay, immunodeficiency, short stature, thrombocytopenia, and acute kidney injury (AKI) resembling atypical hemolytic uremic syndrome. Their heterozygous mother and maternal grandmother show an attenuated phenotype with skewed X-inactivation in blood. AKI in the male patients proved fully responsive to treatment with the complement inhibitor Eculizumab. This germline variant occurs within the transmembrane domain of Cosmc, resulting in dramatically reduced expression of the Cosmc protein. Although A20D-Cosmc is functional, its decreased expression, though in a cell or tissue-specific manner, causes a large reduction of T-synthase protein and activity, which accordingly leads to expression of varied amounts of pathological Tn-antigen (GalNAcα1-O-Ser/Thr/Tyr) on multiple glycoproteins. Transient transfection of patient lymphoblastoid cells with wild-type C1GALT1C1 partially rescued the T-synthase and glycosylation defect. Interestingly, all four affected individuals have high levels of galactose-deficient IgA1 in sera. These results demonstrate that the A20D-Cosmc mutation defines a novel O-glycan chaperonopathy and causes the altered O-glycosylation status in these patients.
2014-03-14 | A Golgi-localized Mannosidase (MAN1B1) Plays a Non-enzymatic Gatekeeper Role in Protein Biosynthetic Quality Control
Conformation-based disorders are manifested at the level of protein structure, necessitating an accurate understanding of how misfolded proteins are processed by the cellular proteostasis network. Asparagine-linked glycosylation plays important roles for protein quality control within the secretory pathway. The suspected role for the MAN1B1 gene product MAN1B1, also known as ER mannosidase I, is to function within the ER similar to the yeast ortholog Mns1p, which removes a terminal mannose unit to initiate a glycan-based ER-associated degradation (ERAD) signal. However, we recently discovered that MAN1B1 localizes to the Golgi complex in human cells and uncovered its participation in ERAD substrate retention, retrieval to the ER, and subsequent degradation from this organelle. The objective of the current study was to further characterize the contribution of MAN1B1 as part of a Golgi-based quality control network. Multiple lines of experimental evidence support a model in which neither the mannosidase activity nor catalytic domain is essential for the retention or degradation of the misfolded ERAD substrate Null Hong Kong. Instead, a highly conserved, vertebrate-specific non-enzymatic decapeptide sequence in the luminal stem domain plays a significant role in controlling the fate of overexpressed Null Hong Kong. Together, these findings define a new functional paradigm in which Golgi-localized MAN1B1 can play a mannosidase-independent gatekeeper role in the proteostasis network of higher eukaryotes. Conformation-based disorders are manifested at the level of protein structure, necessitating an accurate understanding of how misfolded proteins are processed by the cellular proteostasis network. Asparagine-linked glycosylation plays important roles for protein quality control within the secretory pathway. The suspected role for the MAN1B1 gene product MAN1B1, also known as ER mannosidase I, is to function within the ER similar to the yeast ortholog Mns1p, which removes a terminal mannose unit to initiate a glycan-based ER-associated degradation (ERAD) signal. However, we recently discovered that MAN1B1 localizes to the Golgi complex in human cells and uncovered its participation in ERAD substrate retention, retrieval to the ER, and subsequent degradation from this organelle. The objective of the current study was to further characterize the contribution of MAN1B1 as part of a Golgi-based quality control network. Multiple lines of experimental evidence support a model in which neither the mannosidase activity nor catalytic domain is essential for the retention or degradation of the misfolded ERAD substrate Null Hong Kong. Instead, a highly conserved, vertebrate-specific non-enzymatic decapeptide sequence in the luminal stem domain plays a significant role in controlling the fate of overexpressed Null Hong Kong. Together, these findings define a new functional paradigm in which Golgi-localized MAN1B1 can play a mannosidase-independent gatekeeper role in the proteostasis network of higher eukaryotes.
2005-11-16 | Differential Susceptibility of Transferrin Glycoforms to Chymotrypsin: A Proteomics Approach to the Detection of Carbohydrate-Deficient Transferrin
Transferrin exhibits heterogeneity in glycosylation characteristic of pathological changes in alcohol abuse and congenital disorders in glycosylation. This study investigated an alternative approach in the detection of carbohydrate-deficient transferrin based on the premise that glycosylation may afford some degree of protection to proteolytic action. Differential susceptibility to proteolysis by chymotrypsin was demonstrated for normal glycosylated and nonglycosylated recombinant human transferrin, using reverse-phase (RP) HPLC, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and LC-tandem mass spectrometry (MS/MS). Peptide fragmentation profiles were consistent with a predominantly high-specificity cleavage pattern of chymotrypsin. The observed peptide fragmentation profile showed that the C-lobe of recombinant full-length nonglycosylated transferrin (rhTf-NG) appeared to be preferentially cleaved, while cleavage of the N-lobe was restricted to the N-terminal and link sequence regions. Although chymotryptic cleavage sites abound in the N-lobe, their resistance to cleavage was independent of glycosylation. Compared to previous studies of lactoferrin, our data suggest disparity in the role by which glycosylation exerts a protective effect in the siderophilin family. It was clear from the transferrin digestions analyzed by HPLC that N-linked glycosylation did confer protection from proteolysis by chymotrypsin. After fragmentation, a range of peptides representing previously cryptic epitopes were identified as potential candidates for an immunological approach to differentiate between the different transferrin glycoforms. Based on its proximity to the Asn413 glycosylation site, a 15-mer peptide, m/z 1690.472 (NKSDNCEDTPEAGYF), was identified as a suitable candidate for raising anti-peptide antibodies for subsequent immunological detection. This novel approach could form the basis for an alternative assay or reference method for the detection of carbohydrate-deficient transferrin.
small molecules
2026-08-07 | Hypoglycosylation lowers the mechanical activation threshold of Piezo1 and enhances cortical neuronal mechanotransduction: implications for PMM2-CDG
Abstract Piezo1 is a mechanically activated cation channel whose N-linked glycans support protein maturation and plasma membrane trafficking, but their contribution to mechanical gating is unknown. We asked whether hypoglycosylation alters Piezo1 mechanosensitivity and cortical neuronal mechanotransduction, with potential relevance to neurological manifestations of congenital disorders of glycosylation (CDG). Human Piezo1 was studied in HEK293 cells after mutation of two conserved cap-domain N-glycosylation sites or inhibition of N-glycan maturation with swainsonine or kifunensine. Mechanically activated currents were recorded by cell-attached patch-clamp during incremental negative-pressure pulses, whereas Ca 2+ responses were measured during uniaxial stretch. Piezo1 abundance, synaptic localisation and stretch-evoked Ca 2+ signals were also examined in primary mouse cortical neurons. On poly-L-lysine, N2293Q or N2330Q shifted the pressure-response relationship towards lower activating pressures without changing maximal current or inactivation kinetics. This effect was absent on collagen. Swainsonine and kifunensine reduced mature Piezo1 glycosylation and lowered the mechanical activation threshold. Hypoglycosylation enhanced Ca 2+ entry during submaximal stretch in HEK293 cells. In cortical neurons, inhibition of glycan maturation increased somatic Piezo1 immunoreactivity without changing its association with synaptic markers, and potentiated Ca 2+ responses to both the Piezo1 activator Yoda1 and submaximal stretch. Thus, mature N-glycans and the extracellular adhesive environment jointly set Piezo1’s mechanical activation threshold rather than merely regulating biosynthesis and trafficking. These findings establish glycosylation-mechanics coupling as a determinant of neuronal force sensing and suggest that, by facilitating Piezo1 recruitment, defective glycosylation may increase cortical vulnerability to mechanical stress, potentially contributing to head trauma-triggered neurological episodes in phosphomannomutase 2 deficiency (PMM2-CDG). Key points Piezo1 channels convert mechanical forces into electrical and calcium signals. N-linked glycans support channel trafficking to the plasma membrane, but whether they tune the force needed for Piezo1 activation was unknown. Mutating either of two conserved N-glycosylation sites in Piezo1 cap domain, or pharmacologically restricting N-glycan maturation, lowered channel’s mechanical activation threshold without changing maximal current or inactivation. This sensitisation depended on the adhesive substrate (occurred on poly-L-lysine but not collagen), and was most evident during submaximal stretch, showing that glycosylation and the extracellular mechanical environment jointly determine Piezo1 force sensing. In mouse cortical neurons, impaired N-glycan maturation increased somatic Piezo1 abundance and enhanced Ca 2+ responses to its chemical activator Yoda1 and stretch, without changing synaptic localisation. By allowing weak mechanical inputs to recruit Piezo1 more effectively, defective glycosylation may increase cortical responses to mechanical stress and help explain susceptibility to head trauma-triggered neurological episodes in phosphomannomutase 2 deficiency (PMM2-CDG).
2026-07-29 | Repurposing the HMG-CoA reductase inhibitor atorvastatin for SRD5A3-congenital disorder of glycosylation
Abstract Background Steroid 5 alpha-reductase 3-related congenital disorder of glycosylation (SRD5A3-CDG) is a rare inherited disease characterized by neurological dysfunction, including ataxia, as well as developmental and visual impairments, with no approved treatments. The disease is caused by defects in dolichol biosynthesis, a pathway essential for protein glycosylation. However, the lack of suitable in vivo models has limited both mechanistic insight and therapeutic development. Methods We generated a Caenorhabditis elegans model carrying a patient-relevant loss-of-function mutation and performed a motility-based phenotypic drug repurposing screen to identify compounds that improve disease-relevant phenotypes. Lead compounds were evaluated in behavioral, neuronal, and metabolomic assays in worms and in fibroblasts from four individuals with SRD5A3-CDG. Results Here we show that SRD5A3-deficient worms exhibit developmental delay, neuronal dysfunction, and metabolic alterations consistent with dysregulation of the mevalonate pathway. The screen identifies multiple classes of compounds that improve motility, including the cholesterol-lowering drug atorvastatin. Atorvastatin improves multiple disease-relevant phenotypes in the worm model. In patient-derived fibroblasts, treatment partially restores the balance between polyprenol and dolichol, which is disrupted in SRD5A3-CDG. Conclusions These findings establish an in vivo model of SRD5A3-CDG and identify modulation of the mevalonate pathway as a potential therapeutic strategy. The results support further investigation of atorvastatin as a repurposed treatment and demonstrate an approach for combining model organism screening with human cell validation to accelerate rare disease drug discovery.
2026-07-10 | B4GALT5 deficiency impairs glycosphingolipid biosynthesis: a new Congenital Disorder of Glycosylation?
Lactosylceramide is a glycosphingolipid precursor synthesized by two dedicated galactosyltransferases, B4GALT5 and B4GALT6. The specific roles of B4GALT5 and B4GALT6 in humans have not yet been clearly defined. Here, we report the first human case with bi-allelic loss-of-function variants in B4GALT5, suggesting that intact B4GALT5 activity is indispensable for normal glycosphingolipid biosynthesis and human development. We identified bi-allelic variants in the B4GALT5 gene in a child presenting with microcephaly, mild cognitive impairment, and bilateral cataracts. B4GALT5/6 double KO cells transfected with B4GALT5 carrying either of the variants identified in the patient lacked lactosylceramide synthase activity and failed to produce glycosphingolipids. In-silico analyses predicted decreased protein stability and impaired UDP-Gal binding for both B4GALT5 variants. Together, these findings indicate that both variants result in deficient B4GALT5 activity, leaving B4GALT6 as the sole source of lactosylceramide synthase activity. Consistent with this, patient plasma and fibroblasts exhibited an approximately 80% reduction in glycosphingolipid levels compared with healthy controls. Unexpectedly, when expressed in model cells human B4GALT6 displayed lower expression and lower catalytic activity, than human B4GALT5, raising questions about its capacity to compensate for B4GALT5 deficiency. In conclusion, we identified a potential new congenital disorder of glycosylation caused by deficient lactosylceramide synthase activity that may be insufficient to support glycosphingolipids synthesis at levels required for normal brain function.
2026-06-30 | Management of pregnancy and outcomes in a woman with mannose-6-phosphate isomerase deficiency (MPI-CDG).
Congenital Disorder of Glycosylation type Ib (MPI-CDG) is a rare autosomal recessive metabolic disorder caused by deficiency of mannose-6-phosphate isomerase, resulting in impaired N-glycosylation. Unlike other CDG subtypes, MPI-CDG is not associated with neurodevelopmental impairment and is effectively treated with oral D-mannose supplementation. However, evidence guiding management during pregnancy is scarce, and D-mannose is generally avoided due to limited safety data. We describe the long-term course and pregnancy outcomes of a woman diagnosed with MPI-CDG in infancy. She was treated with oral D-mannose throughout childhood with good clinical response but demonstrated intermittent non-compliance in adulthood, complicated by hepatic fibrosis, protein-losing enteropathy, osteoporosis, anaemia, and musculoskeletal manifestations. She had two pregnancies without D-mannose supplementation. The first pregnancy was complicated by microcytic anaemia, hypoalbuminemia, pregnancy-induced cholestasis, and emergency caesarean section. A male infant was delivered and later diagnosed with Hirschsprung disease, requiring surgical correction with good outcome. Postpartum assessment of the mother demonstrated progression of liver disease to cirrhosis (F4). The second pregnancy proceeded with fewer complications and resulted in emergency caesarean delivery of a healthy female infant with normal postnatal glucose control and growth. This case contributes to the limited literature on pregnancy in MPI-CDG and illustrates that successful pregnancies are possible despite advanced multisystem disease and cessation of D-mannose therapy. It highlights the importance of multidisciplinary care, close hepatic and nutritional monitoring, and the need for further studies to clarify the safety and role of D-mannose supplementation during pregnancy.
2026-06-11 | Recurrent hemophagocytic lymphohistiocytosis in COG deficiency: a case series and systematic review of inflammatory manifestations.
Conserved oligomeric Golgi (COG) deficiencies are rare congenital disorders of glycosylation characterized by severe multisystem involvement. Recurrent inflammatory episodes have been reported but remain poorly understood and are likely underrecognized. We describe three patients with COG6 or COG7 deficiency presenting recurrent episodes of hemophagocytic lymphohistiocytosis (HLH). In parallel, we conducted a systematic review of the literature to assess the frequency and characteristics of inflammatory manifestations in COG deficiency. All three patients experienced recurrent febrile episodes associated with biological features of HLH. In two cases, these episodes were followed by neurological deterioration and onset of epilepsy. Early or prophylactic corticosteroid therapy during febrile episodes appeared to mitigate both the severity and neurological impact of inflammatory flares. The literature review identified recurrent, unexplained, and poorly tolerated febrile episodes in approximately 40% of reported patients. Only one additional case of fully documented HLH was identified. However, multiple reports described partial or suggestive HLH features, supporting the hypothesis that hyperinflammatory manifestations are underdiagnosed in this population. COG deficiencies, especially COG6 and COG7, may be complicated by recurrent and potentially severe hyperinflammatory episodes, including HLH, with significant neurological consequences. These findings suggest a link between glycosylation defects and immune dysregulation. Early recognition and preventive anti-inflammatory strategies are recommended.
gene therapies
2026-01-01 | Modeling human PMM2-CDG in medaka to understand systemic effects of hypoglycosylation on development
Congenital disorders of glycosylation (CDG) are a group of rare metabolic diseases caused by mutations in the enzymes involved in glycosylation. To date, no conclusive pathogenic mechanism is linked to the disease and there are only limited therapeutic options available. The most common form of CDG is caused by compound heterozygous hypomorphic alleles of the cytosolic enzyme Phosphomannomutase 2 (PMM2), leading to global protein hypoglycosylation and a multiorgan phenotype in patients. Complete loss-of-function mutations in the essential protein are incompatible with life. Patients that survive carry mutations that lead to reduced enzyme activity of PMM2. PMM2 plays a crucial role at the basis of the glycosylation cascade in the endoplasmic reticulum by providing the essential mannose precursor required for the three glycosylation routes N-glycosylation, O- and C-mannosylation. The entire glycosylation machinery is evolutionarily highly conserved which allows generating translational models in other organisms. The small teleost medaka (Oryzias latipes) offers a great advantage as model organism to investigate the early embryogenesis through the extrauterine and transparent developing embryos. To understand acute effects of Pmm2 loss on development and disease progression, I have created translational models that mimic the reduced residual enzyme activity of PMM2-CDG patients. I followed two routes to investigate the role of PMM2 on development: establish a conditional knockdown system for acute Pmm2 interference at the protein level and patient-based genetic models by precision genome editing in medaka. For the conditional knockdown in medaka, I applied an inducible degron system to selectively degrade Pmm2-GFP, mimicking reduced enzyme activity. To generate patient-based pmm2 alleles, I used canonical base editing to generate the p.C139R mutation and a deletion variant. Further, I developed and carefully examined a novel two step one-shot base editing approach termed “inception”. Inception introduces a new binding site for a second base editing event that subsequently leads to the anticipated edit. With inception I created one of the common patient mutations p.F119L. Depending on the generated alleles, different pmm2 variants resulted in varying enzymatic activity in medaka, phenocopied the patient symptoms and caused hypoglycosylation of proteins. Bottom-up proteomics revealed molecular changes already present before the onset of multisystemic phenotypes, affecting particularly mRNA processing and eye development.
2025-11-03 | AAV9-mediated NGLY1 gene replacement suppresses non-epileptic convulsions in Ngly1-/- rats.
N-glycanase 1 (NGLY1) deficiency is a rare autosomal-recessive neurological disorder characterized by neurological dysfunction and so far, has no effective therapy. A systemic Ngly1-/- rat model recapitulates many patient symptoms, including developmental delay, motor and cognitive deficits. Here we carried out further detailed phenotypic analyses for the Ngly1-/- rats, with particular focus on those easily translatable to patients' symptoms, i.e. sleep disturbances, EEG abnormalities and convulsive behaviors. EEG/EMG recordings revealed fragmented sleep and frequent spontaneous epileptiform discharges in Ngly1-/- rats. Continuous video-EEG monitoring confirmed a high incidence of convulsive events with/without epileptic discharge. At three weeks of age, Ngly1-/- rats received a single intracerebroventricular injection of AAV9-hNGLY1. We then examined whether central nervous system-targeted gene therapy using an adeno-associated virus serotype 9 carrying human NGLY1 (AAV9-hNGLY1) can rescue those phenotypes. While NGLY1 protein was robustly expressed in the brain with partial restoration of enzymatic deglycosylation activity, AAV9-hNGLY1-treated Ngly1-/- rats showed no significant improvement in EEG abnormalities or sleep disruption. In sharp contrast, AAV9-hNGLY1 significantly reduced the frequency of non-epileptic convulsive episodes. These findings expand the phenotypic characterization of the Ngly1-/- rat model to include sleep and seizure phenotypes and demonstrate that AAV9-mediated NGLY1 restoration can suppress overt motor convulsions. On the other hand, persistent EEG seizures and sleep disturbances indicate only a partial therapeutic benefit, underscoring the need for further refinement of gene therapy strategies, as well as additional therapeutic options, for NGLY1 deficiency.
2025-08-20 | AAV-based gene replacement reverses Neurexin-2 downregulation in the cerebellum of a mouse model of phosphomannomutase 2 deficiency (PMM2-CDG).
Phosphomannomutase 2 (PMM2) deficiency is the most common congenital disorders of glycosylation (CDG) with an estimated incidence ranging from 1:20,000 to 1:80,000. Patients manifest a broad spectrum of clinical manifestations, with neurological deficits often emerging as the earliest sign, and may progress to severe multi-organ dysfunction. Mortality reaches 20% by the age of six, primarily due to severe infections, liver insufficiency, or cardiomyopathy. The pathophysiology of the tissue-specific complications remains unclear and there is currently no cure for the disease. In this study, we performed omics analyses of cerebella isolated from a mouse model of PMM2-CDG. RNA-Seq analysis revealed altered gene expression in pathways involved in immune responses and coagulation, while proteomic analysis of proteins enriched by lectin-affinity chromatography identified proteins required for neurodevelopment and neurotransmission. We validated our results by demonstrating significant downregulation of Neurexin-2 in the Pmm2 knockout (KO) mouse cerebella and showed that its reduced abundance can be reversed by AAV9- PMM2 gene treatment of the Pmm2 KO mice.
2025-08-14 | Are viral vector-mediated therapies compatible with aberrant glycosylation?
The ability of adeno-associated viruses (AAVs) to transduce host cells relies on interactions with glycan moieties on the cellular surface. Consequently, disrupted protein glycosylation, which is seen in a range of neurodevelopmental and neurodegenerative diseases, could impair transduction efficiency. Understanding how altered glycosylation impacts AAV binding is essential to optimize AAV-mediated therapeutic strategies. We used glycoproteomics data from cortical brain organoids and iCardiomyocytes of individuals with congenital disorders of glycosylation (CDG) (ALG13-, PMM2-, and PGM1-CDG) to examine the abundance of AAV-binding glycan species. Additionally, we assessed the abundance of coreceptors in proteomics data. We found that the abundance of AAV-binding glycan species was downregulated for all CDG subtypes, but this was significant only for AAV5-, AAV8-, and AAV9-binding glycan motifs in PGM1-CDG. The proteomics data showed significantly decreased abundance of the coreceptor PDGFRβ in ALG13-CDG. The downregulation of glycan species and AAV coreceptors in models of aberrant protein glycosylation underscores the need to optimize AAV selection for conditions with altered protein glycosylation, including CDG and neurodegenerative diseases such as Parkinson's and Alzheimer's disease.
2025-03-18 | AAV-based gene replacement therapy prevents and halts manifestation of abnormal neurological phenotypes in a novel mouse model of PMM2-CDG.
Inherited Phosphomannomutase 2 (PMM2) deficiency, also known as PMM2-CDG, is the most prevalent N-linked congenital disorder of glycosylation (CDG), occurring in approximately 1 in 20,000 individuals in certain populations. Patients exhibit a spectrum of symptoms, with neurological involvement being a prominent feature, often manifesting as the initial clinical sign, and can range from isolated neurological deficits to severe multi-organ dysfunction. Given the absence of curative treatments and a high mortality rate before the age of two, alongside considerable lifelong morbidity, there is an urgent need for innovative therapeutic approaches. To address this unmet need, we developed a tamoxifen-inducible Pmm2 knockout (KO) mouse model with widespread tissue deficiency of Pmm2 expression. Characterization of the mouse model to-date revealed distinct neurological phenotypes relevant to PMM2-CDG, as assessed by the Composite Phenotype Scoring System and Open Field Test. Notably, PMM2 augmentation through AAV9-PMM2 gene replacement therapy prevented and halted the disease-relevant neurological phenotypes induced by Pmm2 KO in the animals. These findings underscored the promise of AAV9-PMM2 gene replacement in managing PMM2-CDG.
proteins
2026-07-07 | Structural insights into mutated human phosphoglucomutase 1 (PGM1) using computational approaches
The phosphoglucomutase 1 (PGM1) enzyme plays a critical role in metabolism and glycosylation in the human body. PGM1 has been linked to multiple disease phenotypes, including the inherited metabolic disorder known as congenital disorders of glycosylation (CDGs). Numerous clinical studies have shown that mutations in key regions of the PGM1 gene affect catalytic activity and induce folding defects of the enzyme. To delve into molecular changes at the supramolecular level, the structural, stability, and other features of PGM1 variants (T19A, N38Y, and D62H) were studied in the present work. To this end, molecular dynamics (MD) simulation at a long timescale (500 ns) was carried out. Parameters such as root-mean-square deviation (RMSD), root-mean-square fluctuations (RMSF), radius of gyration (Rg), solvent-accessible surface area (SASA), hydrogen bonds, and free energy landscape (FEL) were studied and compared with those of the wild-type PGM1. It was noted that mutations 19 A, N38Y, and D62H significantly alter the protein’s structural behavior, causing increased flexibility, reduced stability, and compactness.
2026-07-02 | Effects of Deficient Glycosylation and Deglycosylation on Sperm Condition in Zebrafish ( Danio rerio )
Abstract Congenital disorders of glycosylation and deglycosylation are rare, serious, and lethal disorders afflicting humans. CDGs and CDDGs result in loss of function enzymes which fail to build or break down oligosaccharides on proteins. This can produce protein aggregates and, in turn, reactive oxygen species that harm the cell eventually leading to autophagy and apoptosis. Because sperm contain high concentrations of polyunsaturated fatty acids, they are especially sensitive to these effects, which is understood as one of the leading factors in human male infertility. Sperm are developed in zebrafish similarly to humans and are useful models to examine human reproductive health, as well as genetic disorders. The combination of these advantages makes the analysis of sperm from zebrafish with heterozygous ALG1 or DPAGT1 CDGs or the NGLY1 CDDG suitable. Analysis of sperm concentration, motility, status, viability, and hypoosmotic swelling demonstrated the effects of these disorders on sperm quality. Results showed a significant decrease in sperm concentration, motility, and hypoosmotic swelling for all mutant zebrafish compared to the wild type. This suggests that CDGs and CDDGs influence the amount of sperm produced, the percentage of sperm cells that are mobile, and the integrity of the plasma membrane.
2026-06-01 | Resistant Epilepsy and Developmental Delay in a Syndromic Infant: A Case of Congenital Disorder of Glycosylation Type Ik From India.
Type I congenital disorder of glycosylation (CDG) is a group of genetic disorders that affect the biosynthesis of dolichol-linked oligosaccharides or the transfer of oligosaccharides onto nascent glycoproteins. Mutations in the ALG1 gene cause CDG type Ik. We report a ten-month-old female with CDG type Ik presenting with recurrent seizures, global developmental delay, hypotonia, and dysmorphic features. Whole-exome sequencing revealed a homozygous likely pathogenic variant chr16:5071980G>T or c.131G>T or p.Gly44Val in the ALG1 gene. Transferrin isoform analysis showed a CDG type I pattern, consistent with a glycosylation disorder. This case emphasizes the importance of early clinical suspicion, metabolic screening, and genetic testing in infants with unexplained recurrent seizures, syndromic features, and multisystemic involvement.
2026-05-27 | The revised three-step detour pathway in dolichol biosynthesis is evolutionarily conserved in budding yeast.
The identification of SRD5A3, a causative gene for congenital disorders of glycosylation (CDGs), together with its yeast ortholog DFG10, established the prevailing model that dolichol is synthesized from polyprenol in a single step. Subsequently, a recent discovery of DHRSX in CDG patients revised this view and led to the proposal of a three-step detour pathway for dolichol biosynthesis. However, it remains unclear whether this pathway represents a conserved mechanism or reflects evolutionary diversity in eukaryotes. Here, we identified TDA5 as a yeast ortholog of DHRSX. Deletion of TDA5 caused glycosylation defects, reduced dolichol levels, and accumulated polyprenol. All these phenotypes were rescued by expression of DHRSX, but not by DFG10 or SRD5A3. These findings show that Tda5 serves the same function as DHRSX in yeast, thereby demonstrating conservation of the three-step detour pathway in yeast and supporting a broader eukaryotic framework for dolichol biosynthesis.
2026-05-01 | The role of GMDS mutation in fucosylation disease pathogenesis and hair cell regeneration in zebrafish
Fucosylation is an essential cellular process involved in development, organ maintenance, and tissue repair. Defective fucosylation has been implicated in several human diseases, including early-onset and adult late-onset complex diseases. This work has investigated the role of the GDP-mannose 4,6-dehydratase (GMDS) enzyme gene, required for the rate-limiting reaction for GDP-fucose synthesis, in congenital disorders of glycosylation (CDGs), glaucoma pathogenesis, and hair cell regeneration for hearing loss therapeutic development using zebrafish (Danio rerio). Using molecular, genetic, histological, and imaging techniques, this project has successfully modeled clinical features of CDG patients due to defective fucosylation. Zebrafish gmds⁻ᐟ⁻ mutants (gmdsⁿᶠˡ²) at two days post fertilization (dpf) significantly replicated major clinical features of CDGs reported in patients, such as seizure, epilepsy, and defective neuronal coordination. In addition, this work reveals defective Crystallin protein stress response as the main mechanism of GMDS’s role in glaucoma development risk and confirms an earlier genome wide association studies (GWAS)’s findings, which found GMDS single nucleotide polymorphisms (SNPs) associated with glaucoma pathogenesis and treatment resistance. Furthermore, the zebrafish gmds⁻ᐟ⁻ mutant used in this study also showed increased capacity to regenerate lateral line neuromast hair cells after neomycin ablation. Zebrafish hair cells share similarity in function and structure to the human inner ear hair cells and share about 76% homologous genes of the human genome, thus making translation to human treatment for hearing loss possible. Overall, these findings establish GMDS as a central regulator of fucosylation-dependent signalling pathways in the eye retina stress response activation, hair cell regeneration, and pathology of congenital disorders of glycosylation due to defective fucosylation.
cell therapies
2026-01-16 | PMM2-CDG and the Role of Liver Transplantation as a Long-Term Solution: A Case Report.
Phosphomannomutase-2 congenital disorder of glycosylation (PMM2-CDG) is the most common congenital disorder of glycosylation, affecting protein glycosylation across multiple organ systems. Hepatic involvement may range from isolated elevations in liver transaminases to end-stage liver disease. Reported outcomes of liver transplantation as a treatment modality are sparse. We describe one of the first reported cases of liver transplantation in a child with PMM2-CDG and interim post-transplant outcomes. This patient was diagnosed at 4 months of age after presenting with failure to thrive, lipodystrophy, hypotonia, developmental delay, elevated transaminases, hypoalbuminemia, and coagulopathy. He developed cirrhosis and portal hypertension as well as sequelae of poor protein glycosylation. All these included coagulopathy, protein-losing enteropathy, and refractory ascites requiring serial intravenous fresh frozen plasma and furosemide. He ultimately underwent a liver transplant, after which his ascites resolved. Post-transplant, he developed new-onset recurrent pericardial effusions, suspected to be from a viral etiology versus extrahepatic manifestations of PMM2-CDG, and elevated transaminases following transplantation. Liver transplantation may offer clinical benefit in PMM2-CDG with severe hepatic involvement, including resolution of ascites and improved quality of life, due to its potential to restore liver glycosylation function. However, this is only a partial correction as persistent extrahepatic manifestations underscore the need for further research into transplant outcomes and systemic disease progression in CDG.
2025-04-25 | Clinical Manifestations of Phosphoglucomutase 3 (PGM3) Deficiency
Background and Aims Phosphoglucomutase 3 (PGM3) deficiency is a congenital disorder of glycosylation characterized by elevated IgE, atopy, recurrent infections, autoimmunity, cognitive impairment, and cytopenias. As more patients have been described, the variability in clinical presentation has become apparent. We aimed to further characterize the phenotype of PGM3 deficiency at our center. Methods Medical records were retrospectively reviewed for 10 patients from 4 families with PGM3 deficiency seen at the NIH Clinical Center. Results Ten patients (7 males and 3 females), aged 5 to 38 years, were evaluated at our center. Atopy was the most common manifestation, with eczema seen in all 10 patients and food and drug allergies in 9 and 8 patients, retrospectively. Sinopulmonary infections were noted in 8 patients, complicated by bronchiectasis in 5, and 5 had viral mucocutaneous infections. Seven patients had varying levels of neurocognitive impairment. Five patients had autoimmunity, including vasculitis in 4, glomerulonephritis in two, and psoriasis in one. Three affected siblings had malignancy: two with EBV-positive Hodgkin’s lymphoma, two with EBV-positive diffuse large B cell lymphoma (including one with prior Hodgkin’s), and one with squamous cell CA (SCC). Additional findings included bony abnormalities in 8 (6 with scoliosis, 2 with endplate abnormalities), single kidney (1), and heart failure (1). Nine patients had lymphopenia, 7 had severe chronic neutropenia (ANC < 500), and one had hemolytic anemia. Bone marrow biopsies were evaluated for 7 patients; three were normocellular despite neutropenia, one was hypocellular with no dysplastic features, and one had erythroid hypercellularity due to chronic hemolysis. One patient is alive and well after hematopoietic cell transplantation (HCT), with resolution of recurrent infections, severe neutropenia, and atopic dermatitis, and one patient had a lung transplant for severe bronchiectasis. There were 3 fatalities between ages 36 and 42 from malignancy (2 with lymphoma and one SCC) and one COVID-related fatality at age 18. Conclusions Although this is a multi-systemic disorder, the 30% mortality in early adulthood due to virally driven malignancies along with severe infection and chronic neutropenia suggests that HCT should be strongly considered.
2024-08-04 | HepG2 PMM2-CDG knockout model: A versatile platform for variant and therapeutic evaluation.
Phosphomannomutase 2 deficiency (PMM2-CDG), the most frequent congenital disorder of glycosylation, is an autosomal recessive disease caused by biallelic pathogenic variants in the PMM2 gene. There is no cure for this multisystemic syndrome. Some of the therapeutic approaches that are currently in development include mannose-1-phosphate replacement therapy, drug repurposing, and the use of small chemical molecules to correct folding defects. Preclinical models are needed to evaluate the efficacy of treatments to overcome the high lethality of the available animal model. In addition, the number of variants with unknown significance is increasing in clinical settings. This study presents the generation of a cellular disease model by knocking out the PMM2 gene in the hepatoma HepG2 cell line using CRISPR-Cas9 gene editing. The HepG2 knockout model accurately replicates the PMM2-CDG phenotype, exhibiting a complete absence of PMM2 protein and mRNA, a 90% decrease in PMM enzymatic activity, and altered ICAM-1, LAMP1 and A1AT glycoprotein patterns. The evaluation of PMM2 disease-causing variants validates the model's utility for studying new PMM2 clinical variants, providing insights for diagnosis and potentially for evaluating therapies. A CRISPR-Cas9-generated HepG2 knockout model accurately recapitulates the PMM2-CDG phenotype, providing a valuable tool for assessing disease-causing variants and advancing therapeutic strategies.
2023-10-23 | MAGT1 deficiency in XMEN disease is associated with severe platelet dysfunction and impaired platelet glycoprotein N-glycosylation.
X-linked immunodeficiency with magnesium defect, Epstein-Barr virus infection, and neoplasia (XMEN) disease is a primary immunodeficiency due to loss-of-function mutations in the gene encoding for magnesium transporter 1 (MAGT1). Furthermore, as MAGT1 is involved in the N-glycosylation process, XMEN disease is classified as a congenital disorder of glycosylation. Although XMEN-associated immunodeficiency is well described, the mechanisms underlying platelet dysfunction and those responsible for life-threatening bleeding events have never been investigated. To assess platelet functions in patients with XMEN disease. Two unrelated young boys, including one before and after hematopoietic stem cell transplantation, were investigated for their platelet functions, glycoprotein expression, and serum and platelet-derived N-glycans. Platelet analysis highlighted abnormal elongated cells and unusual barbell-shaped proplatelets. Platelet aggregation, integrin αIIbβ3 activation, calcium mobilization, and protein kinase C activity were impaired between both patients. Strikingly, platelet responses to protease-activated receptor 1 activating peptide were absent at both low and high concentrations. These defects were also associated with decreased molecular weights of glycoprotein Ibα, glycoprotein VI, and integrin αIIb due to partial impairment of N-glycosylation. All these defects were corrected after hematopoietic stem cell transplantation. Our results highlight prominent platelet dysfunction related to MAGT1 deficiency and defective N-glycosylation in several platelet proteins that could explain the hemorrhages reported in patients with XMEN disease.
2023-06-23 | Homozygous truncating variant in MAN2A2 causes a novel congenital disorder of glycosylation with neurological involvement.
Enzymes of the Golgi implicated in N-glycan processing are critical for brain development, and defects in many are defined as congenital disorders of glycosylation (CDG). Involvement of the Golgi mannosidase, MAN2A2 has not been identified previously as causing glycosylation defects. Exome sequencing of affected individuals was performed with Sanger sequencing of the MAN2A2 transcript to confirm the variant. N-glycans were analysed in patient-derived lymphoblasts to determine the functional effects of the variant. A cell-based complementation assay was designed to assess the pathogenicity of identified variants using MAN2A1/MAN2A2 double knock out HEK293 cell lines. We identified a multiplex consanguineous family with a homozygous truncating variant p.Val1101Ter in MAN2A2. Lymphoblasts from two affected brothers carrying the same truncating variant showed decreases in complex N-glycans and accumulation of hybrid N-glycans. On testing of this variant in the developed complementation assay, we see the complete lack of complex N-glycans. Our findings show that pathogenic variants in MAN2A2 cause a novel autosomal recessive CDG with neurological involvement and facial dysmorphism. Here, we also present the development of a cell-based complementation assay to assess the pathogenicity of MAN2A2 variants, which can also be extended to MAN2A1 variants for future diagnosis.
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2025-09-18 | Table 3_Immunopathology in PMM2-CDG: Defective glycosylation impact in the TNFα -TNFR1 signalling pathway.xlsx
Introduction Glycosylation is a post-translational modification that plays a crucial role in immune system activity. Phosphomannomutase 2-Congenital Disorder of Glycosylation (PMM2-CDG) is a rare genetic disease affecting glycosylation with a multi-systemic impact. PMM2-CDG patients commonly show immune disfunction and elevated pro-inflammatory cytokine levels that may link to other symptoms. However, the underlying immune mechanisms remain unclear. Given Tumour Necrosis Factor (TNF)’s key role in inflammation, this study proposes that defective glycosylation of its receptors disrupts intracellular signalling, leading to changes in the immune response of PMM2-CDG patients. Methods To address this, we applied an integrative approach, combining transcriptomics, glycomics, and immune-related assays to investigate the impact of TNF-a stimulation via TNF receptor 1 (TNFR1) in a cohort of PMM2-CDG patients’ skin fibroblasts. Results Our results reveal a multifaceted disruption of TNF-a signalling in PMM2-CDG fibroblasts. We observed structural abnormalities in TNFR1, including altered receptor shedding. PMM2-CDG cells also showed an altered N-glycosylation profile, affecting particularly, high mannose N-glycans. At transcriptional level, PMM2-CDG cells, especially those bearing the R141H heterozygous variant, exhibited a distinct gene expression profile, after stimulation, characterized by dysregulation of immune and signalling pathways. Functionally, these molecular alterations translated into a diminished secretion of key inflammation and infection mediators, such as interleukin-6 (IL-6) and C-C Motif chemokine ligand 5 (CCL5) upon TNF-a stimulation. Similarly, essential signalling kinases including extracellular-signal-regulated kinase (ERK) 1/2, p38 and c-Jun N- terminal kinase (JNK) 2 showed reduced expression in PMM2-CDG cells, and their expression did not alter following TNF-a stimulation, unlike control cells. Conslusion Our findings point to TNFR1 signalling dysregulation as a key contributor to immune dysfunction in PMM2-CDG. Importantly, our study identifies TNFR1 as a promising therapeutic target, suggesting that strategies aimed at modulating TNFR1 activity or restoring glycosylation homeostasis could provide new approaches for treatment development. This work advances our understanding of PMM2 -CDG immunopathology and opens opportunities for targeted therapeutics.
2023-06-02 | A liposomal carbohydrate vaccine, adjuvanted with an NKT cell agonist, induces rapid and enhanced immune responses and antibody class switching
Congenital disorders of glycosylation (CDGs) are genetic diseases caused by gene defects in glycan biosynthesis pathways, and there is an increasing number of patients diagnosed with CDGs. Because CDGs show many different clinical symptoms, their accurate clinical diagnosis is challenging. Recently, we have shown that liposome nanoparticles bearing the ALG1-CDG and PMM2-CDG biomarkers (a tetrasaccharide: Neu5Ac-α2,6-Gal-β1,4-GlcNAc-β1,4-GlcNAc) stimulate a moderate immune response, while the generated antibodies show relatively weak affinity maturation. Thus, mature antibodies with class switching to IgG are desired to develop high-affinity antibodies that may be applied in medical applications.In the present study, a liposome-based vaccine platform carrying a chemoenzymatic synthesized phytanyl-linked tetrasaccharide biomarker was optimized. The liposome nanoparticles were constructed by dioleoylphosphatidylcholine (DOPC) to improve the stability and immunogenicity of the vaccine, and adjuvanted with the NKT cell agonist PBS57 to generate high level of IgG antibodies. The results indicated that the reformulated liposomal vaccine stimulated a stronger immune response, and PBS57 successfully induce an antibody class switch to IgG. Further analyses of IgG antibodies elicited by liposome vaccines suggested their specific binding to tetrasaccharide biomarkers, which were mainly IgG2b isotypes.Immunization with a liposome vaccine carrying a carbohydrate antigen and PBS57 stimulates high titers of CDG biomarker-specific IgG antibodies, thereby showing great potential as a platform to develop rapid diagnostic methods for ALG1-CDG and PMM2-CDG.
2023-05-24 | Germline C1GALT1C1 mutation causes a multisystem chaperonopathy.
Mutations in genes encoding molecular chaperones can lead to chaperonopathies, but none have so far been identified causing congenital disorders of glycosylation. Here we identified two maternal half-brothers with a novel chaperonopathy, causing impaired protein O-glycosylation. The patients have a decreased activity of T-synthase (C1GALT1), an enzyme that exclusively synthesizes the T-antigen, a ubiquitous O-glycan core structure and precursor for all extended O-glycans. The T-synthase function is dependent on its specific molecular chaperone Cosmc, which is encoded by X-chromosomal C1GALT1C1. Both patients carry the hemizygous variant c.59C>A (p.Ala20Asp; A20D-Cosmc) in C1GALT1C1. They exhibit developmental delay, immunodeficiency, short stature, thrombocytopenia, and acute kidney injury (AKI) resembling atypical hemolytic uremic syndrome. Their heterozygous mother and maternal grandmother show an attenuated phenotype with skewed X-inactivation in blood. AKI in the male patients proved fully responsive to treatment with the complement inhibitor Eculizumab. This germline variant occurs within the transmembrane domain of Cosmc, resulting in dramatically reduced expression of the Cosmc protein. Although A20D-Cosmc is functional, its decreased expression, though in a cell or tissue-specific manner, causes a large reduction of T-synthase protein and activity, which accordingly leads to expression of varied amounts of pathological Tn-antigen (GalNAcα1-O-Ser/Thr/Tyr) on multiple glycoproteins. Transient transfection of patient lymphoblastoid cells with wild-type C1GALT1C1 partially rescued the T-synthase and glycosylation defect. Interestingly, all four affected individuals have high levels of galactose-deficient IgA1 in sera. These results demonstrate that the A20D-Cosmc mutation defines a novel O-glycan chaperonopathy and causes the altered O-glycosylation status in these patients.
2014-03-14 | A Golgi-localized Mannosidase (MAN1B1) Plays a Non-enzymatic Gatekeeper Role in Protein Biosynthetic Quality Control
Conformation-based disorders are manifested at the level of protein structure, necessitating an accurate understanding of how misfolded proteins are processed by the cellular proteostasis network. Asparagine-linked glycosylation plays important roles for protein quality control within the secretory pathway. The suspected role for the MAN1B1 gene product MAN1B1, also known as ER mannosidase I, is to function within the ER similar to the yeast ortholog Mns1p, which removes a terminal mannose unit to initiate a glycan-based ER-associated degradation (ERAD) signal. However, we recently discovered that MAN1B1 localizes to the Golgi complex in human cells and uncovered its participation in ERAD substrate retention, retrieval to the ER, and subsequent degradation from this organelle. The objective of the current study was to further characterize the contribution of MAN1B1 as part of a Golgi-based quality control network. Multiple lines of experimental evidence support a model in which neither the mannosidase activity nor catalytic domain is essential for the retention or degradation of the misfolded ERAD substrate Null Hong Kong. Instead, a highly conserved, vertebrate-specific non-enzymatic decapeptide sequence in the luminal stem domain plays a significant role in controlling the fate of overexpressed Null Hong Kong. Together, these findings define a new functional paradigm in which Golgi-localized MAN1B1 can play a mannosidase-independent gatekeeper role in the proteostasis network of higher eukaryotes. Conformation-based disorders are manifested at the level of protein structure, necessitating an accurate understanding of how misfolded proteins are processed by the cellular proteostasis network. Asparagine-linked glycosylation plays important roles for protein quality control within the secretory pathway. The suspected role for the MAN1B1 gene product MAN1B1, also known as ER mannosidase I, is to function within the ER similar to the yeast ortholog Mns1p, which removes a terminal mannose unit to initiate a glycan-based ER-associated degradation (ERAD) signal. However, we recently discovered that MAN1B1 localizes to the Golgi complex in human cells and uncovered its participation in ERAD substrate retention, retrieval to the ER, and subsequent degradation from this organelle. The objective of the current study was to further characterize the contribution of MAN1B1 as part of a Golgi-based quality control network. Multiple lines of experimental evidence support a model in which neither the mannosidase activity nor catalytic domain is essential for the retention or degradation of the misfolded ERAD substrate Null Hong Kong. Instead, a highly conserved, vertebrate-specific non-enzymatic decapeptide sequence in the luminal stem domain plays a significant role in controlling the fate of overexpressed Null Hong Kong. Together, these findings define a new functional paradigm in which Golgi-localized MAN1B1 can play a mannosidase-independent gatekeeper role in the proteostasis network of higher eukaryotes.
2005-11-16 | Differential Susceptibility of Transferrin Glycoforms to Chymotrypsin: A Proteomics Approach to the Detection of Carbohydrate-Deficient Transferrin
Transferrin exhibits heterogeneity in glycosylation characteristic of pathological changes in alcohol abuse and congenital disorders in glycosylation. This study investigated an alternative approach in the detection of carbohydrate-deficient transferrin based on the premise that glycosylation may afford some degree of protection to proteolytic action. Differential susceptibility to proteolysis by chymotrypsin was demonstrated for normal glycosylated and nonglycosylated recombinant human transferrin, using reverse-phase (RP) HPLC, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and LC-tandem mass spectrometry (MS/MS). Peptide fragmentation profiles were consistent with a predominantly high-specificity cleavage pattern of chymotrypsin. The observed peptide fragmentation profile showed that the C-lobe of recombinant full-length nonglycosylated transferrin (rhTf-NG) appeared to be preferentially cleaved, while cleavage of the N-lobe was restricted to the N-terminal and link sequence regions. Although chymotryptic cleavage sites abound in the N-lobe, their resistance to cleavage was independent of glycosylation. Compared to previous studies of lactoferrin, our data suggest disparity in the role by which glycosylation exerts a protective effect in the siderophilin family. It was clear from the transferrin digestions analyzed by HPLC that N-linked glycosylation did confer protection from proteolysis by chymotrypsin. After fragmentation, a range of peptides representing previously cryptic epitopes were identified as potential candidates for an immunological approach to differentiate between the different transferrin glycoforms. Based on its proximity to the Asn413 glycosylation site, a 15-mer peptide, m/z 1690.472 (NKSDNCEDTPEAGYF), was identified as a suitable candidate for raising anti-peptide antibodies for subsequent immunological detection. This novel approach could form the basis for an alternative assay or reference method for the detection of carbohydrate-deficient transferrin.
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Drug Discovery Landscape
2 orphan drug designations for Congenital disorder of glycosylation.
2 orphan drug designations for Congenital disorder of glycosylation.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
repirinast | small molecules | FDA | 2024-11-07 | — | bloom for a cure LLC |
L-fucose | small molecules | FDA | 2019-01-14 | — | AUG Therapeutics, LLC |
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