RARE DISEASE
Sialidosis type 1
Sialidosis type 1
Sialidosis type 1
Synonyms: Cherry-red spot-myoclonus syndrome, Lipomucopolysaccharidosis, Normomorphic sialidosis
Synonyms: Cherry-red spot-myoclonus syndrome, Lipomucopolysaccharidosis, Normomorphic sialidosis
Synonyms: Cherry-red spot-myoclonus syndrome, Lipomucopolysaccharidosis, Normomorphic sialidosis
Drug discovery
0
drugs
With orphan designations
Overview
Sialidosis type 1 is a rare autosomal recessive lysosomal storage disorder caused by NEU1 gene mutations, resulting in neuraminidase deficiency and impaired degradation of sialoglycoconjugates. It typically manifests in adolescence/early adulthood with progressive myoclonus, ataxia, seizures, and visual decline due to macular cherry-red spots (absent in ~20% of cases). Diagnosis relies on neuraminidase activity assays, urinary oligosaccharide analysis, and genetic testing. No disease-modifying therapies exist; management focuses on symptom control [1][2][4][7][15].
Burden
High morbidity: Progressive motor disability (wheelchair dependence in >70%), vision loss, and refractory myoclonus impair quality of life [5][7][15].
Cognitive preservation contrasts with severe physical decline; mortality often linked to status epilepticus or aspiration [4][15].
Diagnostic delays average 5–10 years due to phenotypic variability and lack of pathognomonic features [4][6][15].
Therapies
Symptomatic care: Perampanel for myoclonus/seizures; physical/occupational therapy; wheelchair assistance in advanced disease [2][7][12].
Experimental approaches: AAV-mediated gene therapy (preclinical success in mice), chaperone proteins (PPCA), and dietary compounds (e.g., betaine) under investigation [3][8][16].
Categories: rare genetic diseases, rare inborn errors of metabolism, rare neurological diseases, rare ophthalmic disorders
Research Papers
61 drug discovery papers about Sialidosis type 1, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
61 drug discovery papers about Sialidosis type 1, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
proteins
2026-01-06 | Failure of Allogeneic Transplant to Correct Sialidosis Despite Early Diagnosis and Full Donor Engraftment of Non-Carrier Leucocytes.
Sialidosis, also known as Mucolipidosis Type I, is a rare condition caused by defects in the NEU1 gene which causes the accumulation of sialylated peptides, oligosaccharides, and glycoproteins leading to neurological decline. Haematopoetic stem cell transplantation has been performed in the symptomatic phase twice in the literature but has failed to prevent deterioration. We report on a case where a 4-year-old child was diagnosed with pre-symptomatic sialidosis due to investigation following the incidental detection of a cherry-red spot prior to the onset of neurological symptoms. We performed haematopoetic stem cell transplantation with a matched unrelated cord blood unit with optimal timing prior to clinical decline, achieving full donor engraftment with a largely uneventful post-transplant recovery followed by a period of relative clinical stability. However, subsequent neurological decline detailed by clinical history and radiological findings has occurred suggesting a lack of disease responsiveness to transplantation despite optimal timing. We go on to provide supporting laboratory investigations detailing sialidosis fibroblast culture as part of a novel cross-correction assay and compare results to other transplant responsive lysosomal storage disorders such as mucopolysaccharidosis type 1-H and detail a lack of cross-correction in concordance with our clinical findings. We conclude that conventional allogeneic haematopoetic stem cell transplantation is not a viable disease-modifying treatment option in sialidosis, even when performed optimally in the pre-symptomatic phase, and suggest that alternative treatment options must be explored to improve outcomes in this condition.
2021-02-03 | Intermittent enzyme replacement therapy with recombinant human β-galactosidase prevents neuraminidase 1 deficiency.
Mutations in the galactosidase β 1 (GLB1) gene cause lysosomal β-galactosidase (β-Gal) deficiency and clinical onset of the neurodegenerative lysosomal storage disease, GM1 gangliosidosis. β-Gal and neuraminidase 1 (NEU1) form a multienzyme complex in lysosomes along with the molecular chaperone, protective protein cathepsin A (PPCA). NEU1 is deficient in the neurodegenerative lysosomal storage disease sialidosis, and its targeting to and stability in lysosomes strictly depend on PPCA. In contrast, β-Gal only partially depends on PPCA, prompting us to investigate the role that β-Gal plays in the multienzyme complex. Here, we demonstrate that β-Gal negatively regulates NEU1 levels in lysosomes by competitively displacing this labile sialidase from PPCA. Chronic cellular uptake of purified recombinant human β-Gal (rhβ-Gal) or chronic lentiviral-mediated GLB1 overexpression in GM1 gangliosidosis patient fibroblasts coincides with profound secondary NEU1 deficiency. A regimen of intermittent enzyme replacement therapy dosing with rhβ-Gal, followed by enzyme withdrawal, is sufficient to augment β-Gal activity levels in GM1 gangliosidosis patient fibroblasts without promoting NEU1 deficiency. In the absence of β-Gal, NEU1 levels are elevated in the GM1 gangliosidosis mouse brain, which are restored to normal levels following weekly intracerebroventricular dosing with rhβ-Gal. Collectively, our results highlight the need to carefully titrate the dose and dosing frequency of β-Gal augmentation therapy for GM1 gangliosidosis. They further suggest that intermittent intracerebroventricular enzyme replacement therapy dosing with rhβ-Gal is a tunable approach that can safely augment β-Gal levels while maintaining NEU1 at physiological levels in the GM1 gangliosidosis brain.
2014-03-27 | Mucopolysaccharidoses and mucolipidoses.
The mucopolysaccharidoses (MPS) and mucolipidoses (ML) are progressive storage disorders that share many clinical features varying from facial dysmorphism, bone dysplasia, hepatosplenomegaly, neurological abnormalities, developmental regression, and a reduced life expectancy at the severe end of the clinical spectrum to an almost normal clinical phenotype and life span in patients with more attenuated disease. MPS and ML are transmitted in an autosomal recessive manner, except for the X-linked MPS II (Hunter syndrome). Diagnosis is initially by detecting partially degraded GAG or oligosaccharide in urine and confirmed by specific enzyme assays in serum, leukocytes, or skin fibroblasts. For the majority of disorders treatment is palliative, but there have been important advances in the use of specific enzyme replacement therapy strategies for some MPS disorders and this is an area of very rapid development. In addition, hematopoietic stem cell transplantation (HSCT) can improve outcome in carefully selected patients with MPS (especially MPS IH, Hurler syndrome), but this procedure is associated with significant risk. Gene augmentation/transfer using a variety of vectors has been successful in animal models but has not yet been successfully performed in a human patient with one of these disorders. It is important to remember that prenatal diagnosis is possible for all of these disorders.
2013-06-12 | Chaperone-mediated gene therapy with recombinant AAV-PPCA in a new mouse model of type I sialidosis
The lysosomal storage disease sialidosis is caused by a primary deficiency of the sialidase N-acetyl-α-neuraminidase-1 (NEU1). Patients with type I sialidosis develop an attenuated, non-neuropathic form of the disease also named cherry red spot myoclonus syndrome, with symptoms arising during juvenile/ adult age. NEU1 requires binding to its chaperone, protective protein/cathepsin A (PPCA), for lysosomal compartmentalization, stability and catalytic activation. We have generated a new mouse model of type I sialidosis that ubiquitously expresses a NEU1 variant carrying a V54M amino acid substitution identified in an adult patient with type I sialidosis. Mutant mice developed signs of lysosomal disease after 1 year of age, predominantly in the kidney, albeit low residual NEU1 activity was detected in most organs and cell types. We demonstrate that the activity of the mutant enzyme could be effectively increased in all systemic tissues by chaperone-mediated gene therapy with a liver-tropic recombinant AAV2/8 vector expressing PPCA. This resulted in clear amelioration of the disease phenotype. These results suggest that at least some of the NEU1 mutations associated with type I sialidosis may respond to PPCA-chaperone-mediated gene therapy.
2010-09-07 | Detection of Neu1 Sialidase Activity in Regulating TOLL-like Receptor Activation
Mammalian Toll-like receptors (TLRs) are a family of receptors that recognize pathogen-associated molecular patterns. Not only are TLRs crucial sensors of microbial (e.g., viruses, bacteria and parasite) infections, they also play an important role in the pathophysiology of infectious diseases, inflammatory diseases, and possibly in autoimmune diseases. Thus, the intensity and duration of TLR responses against infectious diseases must be tightly controlled. It follows that understanding the structural integrity of sensor receptors, their ligand interactions and signaling components is essential for subsequent immunological protection. It would also provide important opportunities for disease modification through sensor manipulation. Although the signaling pathways of TLR sensors are well characterized, the parameters controlling interactions between the sensors and their ligands still remain poorly defined. We have recently identified a novel mechanism of TLR activation by its natural ligand, which has not been previously observed. It suggests that ligand-induced TLR activation is tightly controlled by Neu1 sialidase activation. We have also reported that Neu1 tightly regulates neurotrophin receptors like TrkA and TrkB, which involve Neu1 and matrix metalloproteinase-9 (MMP-9) cross-talk in complex with the receptors. The sialidase assay has been initially use to find a novel ligand, thymoquinone, in the activation of Neu4 sialidase on the cell surface of macrophages, dendritic cells and fibroblast cells via GPCR Gαi proteins and MMP-9. For TLR receptors, our data indicate that Neu1 sialidase is already in complex with TLR-2, -3 and -4 receptors, and is induced upon ligand binding to either receptor. Activated Neu1 sialidase hydrolyzes sialyl α-2,3-linked β-galactosyl residues distant from ligand binding to remove steric hinderance to TLR-4 dimerization, MyD88/TLR4 complex recruitment, NFkB activation and pro-inflammatory cell responses. In a collaborative report, Neu1 sialidase has been shown to regulate phagocytosis in macrophage cells. Taken together, the sialidase assay has provided us with powerful insights to the molecular mechanisms of ligand-induced receptor activation. Although the precise relationship between Neu1 sialidase and the activation of TLR, Trk receptors has yet to be fully elucidated, it would represent a new or pioneering approach to cell regulation pathways.
small molecules
2026-02-10 | Alterations in secondary lipids are associated with neuroinflammation in the brain of Neu1-deficient mice.
Neu1 (lysosomal sialidase 1) is essential for removing sialic acid from oligosaccharides and glycoconjugates. Neu1 deficiency impairs lysosomal digestion, leading to sialidosis and sialoglycoprotein accumulation. It also increases lipids, including gangliosides GM3, GD3, GM4, and LM1, in the kidney, liver, and spleen. Neu1-/- mice display symptoms resembling Type II sialidosis, including enlarged spleen and liver, kidney issues, neurological problems, spinal defects, and oligosaccharide buildup. The study examined secondary lipid alterations and inflammation in the cortex and cerebellum of these mice. Lipidomic, molecular, and immunohistochemical analyses of tissues from 2 and 5 M Neu1-/- mice revealed reduced levels of lipids, including PC, PE, PS, and CL, along with increased pro-inflammatory cytokines and loss of oligodendrocytes and neurons. Signs of astrogliosis and microgliosis emerged in specific brain regions. These results indicate that reduced levels of glycerophospholipids could serve as an indicator of inflammation in sialidosis mice. Future research should investigate therapies targeting these lipid changes, as modulating glycerophospholipids might slow disease progression in sialidosis patients.
2026-02-10 | Sialidosis type I: How to alleviate disabling myoclonic seizures?-A multicenter analysis of eight cases and review of the literature.
Sialidosis type I (ST-1) is an autosomal-recessive, very rare, progressive lysosomal storage disorder caused by pathogenic variants in NEU1. It is clinically characterized by progressive ataxia, myoclonic seizures (MS), bilateral tonic-clonic seizures (BTCS), and distinctive ophthalmological findings. Given the lack of curative options, in this study, we investigated symptomatic treatment strategies, with a particular focus on the efficacy of antiseizure medications (ASMs). We describe the clinical course of a patient followed from diagnosis to 18 years of age, and review seven additional cases from our cohort. In parallel, we conducted a narrative review of the literature (PubMed, January 2010-September 2025) to identify published reports containing therapeutic data. Therapeutic responses were evaluated in a total of 33 cases (8 from our cohort, 25 from published sources). Although available data are insufficient to define standardized treatment guidelines, some ASMs, such as ACZ, PER, LEV, VPA, CZP, and ZNS, demonstrated fairly consistent efficacy in managing MS and BTCS. Sodium oxybate or deep-brain stimulation may be considered in refractory cases. Prospective documentation of clinical course and treatment outcomes-ideally through an international registry-is crucial to improve patient care and inform therapeutic strategies. Sialidosis type I (ST-1) is a very rare genetic disorder causing movement problems and seizures, with no cure available yet. We followed 8 patients and reviewed 25 published cases to assess treatments focusing on myoclonic seizure (MS) control. Some antiseizure medications showed benefit. However, we have too little data to make clear recommendations. To improve patients' treatment and to choose the most appropriate therapy, it would be important to follow patients over a longer period of time, for example, in an international registry.
2023-11-08 | Severe kidney dysfunction in sialidosis mice reveals an essential role for neuraminidase 1 in reabsorption.
Sialidosis is an ultra-rare multisystemic lysosomal disease caused by mutations in the neuraminidase 1 (NEU1) gene. The severe type II form of the disease manifests with a prenatal/infantile or juvenile onset, bone abnormalities, severe neuropathology, and visceromegaly. A subset of these patients present with nephrosialidosis, characterized by abrupt onset of fulminant glomerular nephropathy. We studied the pathophysiological mechanism of the disease in 2 NEU1-deficient mouse models, a constitutive Neu1-knockout, Neu1ΔEx3, and a conditional phagocyte-specific knockout, Neu1Cx3cr1ΔEx3. Mice of both strains exhibited terminal urinary retention and severe kidney damage with elevated urinary albumin levels, loss of nephrons, renal fibrosis, presence of storage vacuoles, and dysmorphic mitochondria in the intraglomerular and tubular cells. Glycoprotein sialylation in glomeruli, proximal distal tubules, and distal tubules was drastically increased, including that of an endocytic reabsorption receptor megalin. The pool of megalin bearing O-linked glycans with terminal galactose residues, essential for protein targeting and activity, was reduced to below detection levels. Megalin levels were severely reduced, and the protein was directed to lysosomes instead of the apical membrane. Together, our results demonstrated that desialylation by NEU1 plays a crucial role in processing and cellular trafficking of megalin and that NEU1 deficiency in sialidosis impairs megalin-mediated protein reabsorption.
2023-06-27 | Targeting shared molecular etiologies to accelerate drug development for rare diseases
Rare diseases affect over 400 million people worldwide and less than 5% of rare diseases have an approved treatment. Fortunately, the number of underlying disease etiologies is far less than the number of diseases, because many rare diseases share a common molecular etiology. Moreover, many of these shared molecular etiologies are therapeutically actionable. Grouping rare disease patients for clinical trials based on the underlying molecular etiology, rather than the traditional, symptom-based definition of disease, has the potential to greatly increase the number of patients gaining access to clinical trials. Basket clinical trials based on a shared molecular drug target have become common in the field of oncology and have been accepted by regulatory agencies as a basis for drug approvals. Implementation of basket clinical trials in the field of rare diseases is seen by multiple stakeholders-patients, researchers, clinicians, industry, regulators, and funders-as a solution to accelerate the identification of new therapies and address patient's unmet needs.
2022-10-17 | Sialidase Inhibitors with Different Mechanisms
Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.
gene therapies
2026-04-01 | Lysosomal Neuraminidase 1 (NEU1): Its Unique Molecular Characters and Therapeutic Approaches for Deficiencies.
Neuraminidase 1 (NEU1) is a lysosomal sialidase that removes terminal α-bound sialic acid from sialylglycoconjugates and contributes to ubiquitous catabolism of sialylglycoconjugates and immunoregulatory functions. Different from other human sialidases, including NEU2 to NEU4, NEU1 is first produced as an N-glycosylated precursor protein, which binds to its protective protein/cathepsin A (CTSA) and then forms a lysosomal multienzyme complex (LMC) with β-galactosidase 1 (GLB1) in the rough endoplasmic reticulum (RER) lumen. NEU1 trafficking to lysosomes and intralysosomal activation under acidic pH conditions essentially requires association with CTSA, which carries terminal mannose 6-phosphate (M6P)-type N-glycan to bind with cation-dependent (CD) M6P receptor (CD-M6PR) in the Golgi apparatus via endosomes. In contrast, the single NEU1 gene overexpression in mammalian cells results in NEU1 protein crystallization in the RER owing to self-aggregation at a relatively low intrinsic CTSA level. Two NEU1 deficiencies, sialidosis (SiD) and galactosialidosis (GS), are caused by autosomal recessive NEU1 and CTSA gene mutations, respectively. These untreatable disorders are associated with excessive storage of sialylglycans in neurovisceral organs and systemic symptoms. We produced a new GS model mouse by introducing a homozygous Ctsa IVS6+1g/a mutation into the murine gene locus, leading to partial exon 6 skipping and simultaneous deficiency of Ctsa and Neu1. The GS mice exhibited clinical symptoms similar to those seen in juvenile/adult GS patients, including myoclonic seizures, suppressed behavior, a gargoyle-like face, edema, proctoptosis owing to Neu1 deficiency, and sialylglycan accumulation related to neurovisceral inflammation. Evaluating the efficacy of a novel therapy utilizing GS and SiD model mice and overcoming the human NEU1 gene product shortage will be necessary for a novel, effective treatment for NEU1 deficiencies.
2025-01-25 | Genetic Insights and Clinical Implications of NEU1 Mutations in Sialidosis
Sialidosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the NEU1 gene, resulting in deficient neuraminidase-1 activity and the subsequent accumulation of sialylated compounds in lysosomes. This review comprehensively analyzes the genetic and clinical heterogeneity associated with sialidosis, emphasizing the distinction between the milder type I form and the more severe type II form. Over 90 pathogenic NEU1 variants, predominantly missense mutations, have been identified, highlighting significant phenotypic diversity. Advancements in genomic sequencing technologies have facilitated the identification of known and novel mutations, with population-specific insights elucidating ethnic variability in symptomatology and genetic profiles. Recent case studies, including a novel compound heterozygous variant, further illustrate the complexity of the genotype–phenotype correlations. Emerging therapeutic approaches, such as enzyme replacement therapy and adeno-associated virus-mediated gene therapy, demonstrate promising potential for restoring neuraminidase-1 function and improving outcomes in preclinical models. This review emphasizes the critical role of genetic analysis in diagnosis and management while advocating for continued research into the molecular mechanisms underlying sialidosis to enable the development of targeted, personalized treatments.
2024-11-28 | Two cases of type I sialidosis and a literature review.
This study aims to compare the clinical and electrophysiological characteristics of two cases of type I sialidosis in Chinese children with those reported in prior literature. The goal is to elucidate the clinical and genetic features of type I sialidosis. Clinical investigations and genetic analyses were conducted on an 11-year-old girl, primarily presenting with short stature, who was admitted in June 2020, and a 10-year-old boy, admitted in July 2023, exhibiting rapid weight gain and accompanying visual impairment as primary manifestations. A literature review was performed by summarizing data from 31 published articles encompassing 69 genetically confirmed cases of type I sialidosis up to 2023 for comparative analysis. Patient 1 exhibited short stature, self-reported poor night vision, a history of occasional febrile seizures, mild scoliosis, bilateral cherry-red spots in the fundus, and prolonged P100 latency in both eyes as observed in visual evoked potentials (VEP). Genetic analysis revealed that she carried compound-heterozygous variants c.239 C > T (p.P80L) and c.880 C > T (p.R294C) in the NEU1 gene, inherited from her parents. Patient 2 presented with rapid weight gain and visual impairment, bilateral cherry-red spots in the fundus, abnormal neuroepithelial layer reflexes in both macular areas, approximately normal P100 latency but severely reduced amplitude in VEP after pupillary dilation, and severe bilateral optic nerve conduction block with relatively normal retinal cell function. Compound-heterozygous variants c.239 C > T (p.P80L) and c.803 A > G (p.T268C) were identified in the NEU1 gene of the Patient 2, inherited from his parents. By combining the cases reported in 31 literature articles with the 2 cases in our study, a total of 71 type I sialidosis patients were analyzed. The most common symptoms observed were muscle spasms (91.5%), followed by ataxia (75%) and seizures (63.6%). Intellectual impairment and abnormal electroencephalograms were more prevalent in Caucasian patients. Additionally, abnormal somatosensory evoked potentials, large cortical waves, and prolonged latency of VEP were more frequently observed in both Asian and Caucasian patients, serving as alternative indicators for early diagnosis. NEU1 gene analysis provides essential guidance for genetic counseling and prenatal diagnosis. The exon 2 variant c.239 C > T (p.P80L) in the NEU1 gene may represent a mutation hotspot among Chinese patients.
2024-11-20 | Lysosomal storage diseases. Mucolipidosis
The epidemiology, clinical, biochemical and molecular genetic characteristics of mucolipidoses — autosomal recessive lysosomal storage diseases that combine the clinical manifestations of mucopolysaccharidoses and sphingolipidoses — are presented. In accordance with the modern classification, types I, II and III mucolipidoses are classified as glycoproteinoses, and type IV mucolipidoses are classified as gangliosidoses. Mucolipidoses type I, or sialidosis, is caused by the presence of inactivating mutations in the α-neuraminidase gene NEU1, and a related disease is galactosialidosis, accompanied by secondary deficiency of α-neuraminidase and β-galactosidase in the CTSA gene of the protective protein cathepsin A. Both diseases are characterized by early progressive delay in psychomotor development, muscle myoclonus, severe ophthalmopathy and early death of patients. The pathogenesis of diseases is associated with excessive accumulation of sialocontaining glycoproteins and oligosaccharides in lysosomes. Hereditary deficiency of N-acetylglucosaminyl-1-phosphotransferase, necessary for the addition of mannose-6-phosphate to the oligosaccharides of lysosomal enzymes, underlies the development of two allelic diseases caused by mutations in the GNPTAB gene mucolipidoses type II, or “I-cell” disease and mucolipidoses type III, alpha/beta or pseudopolydystrophy of Hurler. Mutations in the GNPTG gene, which encodes the gamma subunit of this enzyme, are responsible for the development of the milder type III mucolipidoses (gamma). All these diseases are characterized by impaired phosphorylation and transport of lysosomal enzymes, which is accompanied by severe growth retardation, skeletal abnormalities and early death of patients. Pathogenesis of mucolipidoses type IV, or sialolipidosis, associated with the simultaneous accumulation of phospholipids, sphingolipids, mucopolysaccharides and gangliosides, which occurs as a result of mutations in the MCOLN1 gene, encoding mucolipin 1, which forms a channel localized on the membranes of lysosomes and endosomes, involved in the regulation of lipid and protein transport. The article presents a description of clinical cases of mucolipidosis types II and IIIA. Preclinical trials have shown promise for enzyme replacement therapy, chaperone therapy, and gene therapy for the treatment of sialidosis and galactosialidosis. However, pathogenetic methods of therapy for mucolipidoses have not been described in clinical practice to date.
2024-07-04 | AAV-mediated gene therapy for sialidosis.
Sialidosis (mucolipidosis I) is a glycoprotein storage disease, clinically characterized by a spectrum of systemic and neurological phenotypes. The primary cause of the disease is deficiency of the lysosomal sialidase NEU1, resulting in accumulation of sialylated glycoproteins/oligosaccharides in tissues and body fluids. Neu1-/- mice recapitulate the severe, early-onset forms of the disease, affecting visceral organs, muscles, and the nervous system, with widespread lysosomal vacuolization evident in most cell types. Sialidosis is considered an orphan disorder with no therapy currently available. Here, we assessed the therapeutic potential of AAV-mediated gene therapy for the treatment of sialidosis. Neu1-/- mice were co-injected with two scAAV2/8 vectors, expressing human NEU1 and its chaperone PPCA. Treated mice were phenotypically indistinguishable from their WT controls. NEU1 activity was restored to different extent in most tissues, including the brain, heart, muscle, and visceral organs. This resulted in diminished/absent lysosomal vacuolization in multiple cell types and reversal of sialyl-oligosacchariduria. Lastly, normalization of lysosomal exocytosis in the cerebrospinal fluids and serum of treated mice, coupled to diminished neuroinflammation, were measures of therapeutic efficacy. These findings point to AAV-mediated gene therapy as a suitable treatment for sialidosis and possibly other diseases, associated with low NEU1 expression.
proteins
2026-01-06 | Failure of Allogeneic Transplant to Correct Sialidosis Despite Early Diagnosis and Full Donor Engraftment of Non-Carrier Leucocytes.
Sialidosis, also known as Mucolipidosis Type I, is a rare condition caused by defects in the NEU1 gene which causes the accumulation of sialylated peptides, oligosaccharides, and glycoproteins leading to neurological decline. Haematopoetic stem cell transplantation has been performed in the symptomatic phase twice in the literature but has failed to prevent deterioration. We report on a case where a 4-year-old child was diagnosed with pre-symptomatic sialidosis due to investigation following the incidental detection of a cherry-red spot prior to the onset of neurological symptoms. We performed haematopoetic stem cell transplantation with a matched unrelated cord blood unit with optimal timing prior to clinical decline, achieving full donor engraftment with a largely uneventful post-transplant recovery followed by a period of relative clinical stability. However, subsequent neurological decline detailed by clinical history and radiological findings has occurred suggesting a lack of disease responsiveness to transplantation despite optimal timing. We go on to provide supporting laboratory investigations detailing sialidosis fibroblast culture as part of a novel cross-correction assay and compare results to other transplant responsive lysosomal storage disorders such as mucopolysaccharidosis type 1-H and detail a lack of cross-correction in concordance with our clinical findings. We conclude that conventional allogeneic haematopoetic stem cell transplantation is not a viable disease-modifying treatment option in sialidosis, even when performed optimally in the pre-symptomatic phase, and suggest that alternative treatment options must be explored to improve outcomes in this condition.
2021-02-03 | Intermittent enzyme replacement therapy with recombinant human β-galactosidase prevents neuraminidase 1 deficiency.
Mutations in the galactosidase β 1 (GLB1) gene cause lysosomal β-galactosidase (β-Gal) deficiency and clinical onset of the neurodegenerative lysosomal storage disease, GM1 gangliosidosis. β-Gal and neuraminidase 1 (NEU1) form a multienzyme complex in lysosomes along with the molecular chaperone, protective protein cathepsin A (PPCA). NEU1 is deficient in the neurodegenerative lysosomal storage disease sialidosis, and its targeting to and stability in lysosomes strictly depend on PPCA. In contrast, β-Gal only partially depends on PPCA, prompting us to investigate the role that β-Gal plays in the multienzyme complex. Here, we demonstrate that β-Gal negatively regulates NEU1 levels in lysosomes by competitively displacing this labile sialidase from PPCA. Chronic cellular uptake of purified recombinant human β-Gal (rhβ-Gal) or chronic lentiviral-mediated GLB1 overexpression in GM1 gangliosidosis patient fibroblasts coincides with profound secondary NEU1 deficiency. A regimen of intermittent enzyme replacement therapy dosing with rhβ-Gal, followed by enzyme withdrawal, is sufficient to augment β-Gal activity levels in GM1 gangliosidosis patient fibroblasts without promoting NEU1 deficiency. In the absence of β-Gal, NEU1 levels are elevated in the GM1 gangliosidosis mouse brain, which are restored to normal levels following weekly intracerebroventricular dosing with rhβ-Gal. Collectively, our results highlight the need to carefully titrate the dose and dosing frequency of β-Gal augmentation therapy for GM1 gangliosidosis. They further suggest that intermittent intracerebroventricular enzyme replacement therapy dosing with rhβ-Gal is a tunable approach that can safely augment β-Gal levels while maintaining NEU1 at physiological levels in the GM1 gangliosidosis brain.
2014-03-27 | Mucopolysaccharidoses and mucolipidoses.
The mucopolysaccharidoses (MPS) and mucolipidoses (ML) are progressive storage disorders that share many clinical features varying from facial dysmorphism, bone dysplasia, hepatosplenomegaly, neurological abnormalities, developmental regression, and a reduced life expectancy at the severe end of the clinical spectrum to an almost normal clinical phenotype and life span in patients with more attenuated disease. MPS and ML are transmitted in an autosomal recessive manner, except for the X-linked MPS II (Hunter syndrome). Diagnosis is initially by detecting partially degraded GAG or oligosaccharide in urine and confirmed by specific enzyme assays in serum, leukocytes, or skin fibroblasts. For the majority of disorders treatment is palliative, but there have been important advances in the use of specific enzyme replacement therapy strategies for some MPS disorders and this is an area of very rapid development. In addition, hematopoietic stem cell transplantation (HSCT) can improve outcome in carefully selected patients with MPS (especially MPS IH, Hurler syndrome), but this procedure is associated with significant risk. Gene augmentation/transfer using a variety of vectors has been successful in animal models but has not yet been successfully performed in a human patient with one of these disorders. It is important to remember that prenatal diagnosis is possible for all of these disorders.
2013-06-12 | Chaperone-mediated gene therapy with recombinant AAV-PPCA in a new mouse model of type I sialidosis
The lysosomal storage disease sialidosis is caused by a primary deficiency of the sialidase N-acetyl-α-neuraminidase-1 (NEU1). Patients with type I sialidosis develop an attenuated, non-neuropathic form of the disease also named cherry red spot myoclonus syndrome, with symptoms arising during juvenile/ adult age. NEU1 requires binding to its chaperone, protective protein/cathepsin A (PPCA), for lysosomal compartmentalization, stability and catalytic activation. We have generated a new mouse model of type I sialidosis that ubiquitously expresses a NEU1 variant carrying a V54M amino acid substitution identified in an adult patient with type I sialidosis. Mutant mice developed signs of lysosomal disease after 1 year of age, predominantly in the kidney, albeit low residual NEU1 activity was detected in most organs and cell types. We demonstrate that the activity of the mutant enzyme could be effectively increased in all systemic tissues by chaperone-mediated gene therapy with a liver-tropic recombinant AAV2/8 vector expressing PPCA. This resulted in clear amelioration of the disease phenotype. These results suggest that at least some of the NEU1 mutations associated with type I sialidosis may respond to PPCA-chaperone-mediated gene therapy.
2010-09-07 | Detection of Neu1 Sialidase Activity in Regulating TOLL-like Receptor Activation
Mammalian Toll-like receptors (TLRs) are a family of receptors that recognize pathogen-associated molecular patterns. Not only are TLRs crucial sensors of microbial (e.g., viruses, bacteria and parasite) infections, they also play an important role in the pathophysiology of infectious diseases, inflammatory diseases, and possibly in autoimmune diseases. Thus, the intensity and duration of TLR responses against infectious diseases must be tightly controlled. It follows that understanding the structural integrity of sensor receptors, their ligand interactions and signaling components is essential for subsequent immunological protection. It would also provide important opportunities for disease modification through sensor manipulation. Although the signaling pathways of TLR sensors are well characterized, the parameters controlling interactions between the sensors and their ligands still remain poorly defined. We have recently identified a novel mechanism of TLR activation by its natural ligand, which has not been previously observed. It suggests that ligand-induced TLR activation is tightly controlled by Neu1 sialidase activation. We have also reported that Neu1 tightly regulates neurotrophin receptors like TrkA and TrkB, which involve Neu1 and matrix metalloproteinase-9 (MMP-9) cross-talk in complex with the receptors. The sialidase assay has been initially use to find a novel ligand, thymoquinone, in the activation of Neu4 sialidase on the cell surface of macrophages, dendritic cells and fibroblast cells via GPCR Gαi proteins and MMP-9. For TLR receptors, our data indicate that Neu1 sialidase is already in complex with TLR-2, -3 and -4 receptors, and is induced upon ligand binding to either receptor. Activated Neu1 sialidase hydrolyzes sialyl α-2,3-linked β-galactosyl residues distant from ligand binding to remove steric hinderance to TLR-4 dimerization, MyD88/TLR4 complex recruitment, NFkB activation and pro-inflammatory cell responses. In a collaborative report, Neu1 sialidase has been shown to regulate phagocytosis in macrophage cells. Taken together, the sialidase assay has provided us with powerful insights to the molecular mechanisms of ligand-induced receptor activation. Although the precise relationship between Neu1 sialidase and the activation of TLR, Trk receptors has yet to be fully elucidated, it would represent a new or pioneering approach to cell regulation pathways.
small molecules
2026-02-10 | Alterations in secondary lipids are associated with neuroinflammation in the brain of Neu1-deficient mice.
Neu1 (lysosomal sialidase 1) is essential for removing sialic acid from oligosaccharides and glycoconjugates. Neu1 deficiency impairs lysosomal digestion, leading to sialidosis and sialoglycoprotein accumulation. It also increases lipids, including gangliosides GM3, GD3, GM4, and LM1, in the kidney, liver, and spleen. Neu1-/- mice display symptoms resembling Type II sialidosis, including enlarged spleen and liver, kidney issues, neurological problems, spinal defects, and oligosaccharide buildup. The study examined secondary lipid alterations and inflammation in the cortex and cerebellum of these mice. Lipidomic, molecular, and immunohistochemical analyses of tissues from 2 and 5 M Neu1-/- mice revealed reduced levels of lipids, including PC, PE, PS, and CL, along with increased pro-inflammatory cytokines and loss of oligodendrocytes and neurons. Signs of astrogliosis and microgliosis emerged in specific brain regions. These results indicate that reduced levels of glycerophospholipids could serve as an indicator of inflammation in sialidosis mice. Future research should investigate therapies targeting these lipid changes, as modulating glycerophospholipids might slow disease progression in sialidosis patients.
2026-02-10 | Sialidosis type I: How to alleviate disabling myoclonic seizures?-A multicenter analysis of eight cases and review of the literature.
Sialidosis type I (ST-1) is an autosomal-recessive, very rare, progressive lysosomal storage disorder caused by pathogenic variants in NEU1. It is clinically characterized by progressive ataxia, myoclonic seizures (MS), bilateral tonic-clonic seizures (BTCS), and distinctive ophthalmological findings. Given the lack of curative options, in this study, we investigated symptomatic treatment strategies, with a particular focus on the efficacy of antiseizure medications (ASMs). We describe the clinical course of a patient followed from diagnosis to 18 years of age, and review seven additional cases from our cohort. In parallel, we conducted a narrative review of the literature (PubMed, January 2010-September 2025) to identify published reports containing therapeutic data. Therapeutic responses were evaluated in a total of 33 cases (8 from our cohort, 25 from published sources). Although available data are insufficient to define standardized treatment guidelines, some ASMs, such as ACZ, PER, LEV, VPA, CZP, and ZNS, demonstrated fairly consistent efficacy in managing MS and BTCS. Sodium oxybate or deep-brain stimulation may be considered in refractory cases. Prospective documentation of clinical course and treatment outcomes-ideally through an international registry-is crucial to improve patient care and inform therapeutic strategies. Sialidosis type I (ST-1) is a very rare genetic disorder causing movement problems and seizures, with no cure available yet. We followed 8 patients and reviewed 25 published cases to assess treatments focusing on myoclonic seizure (MS) control. Some antiseizure medications showed benefit. However, we have too little data to make clear recommendations. To improve patients' treatment and to choose the most appropriate therapy, it would be important to follow patients over a longer period of time, for example, in an international registry.
2023-11-08 | Severe kidney dysfunction in sialidosis mice reveals an essential role for neuraminidase 1 in reabsorption.
Sialidosis is an ultra-rare multisystemic lysosomal disease caused by mutations in the neuraminidase 1 (NEU1) gene. The severe type II form of the disease manifests with a prenatal/infantile or juvenile onset, bone abnormalities, severe neuropathology, and visceromegaly. A subset of these patients present with nephrosialidosis, characterized by abrupt onset of fulminant glomerular nephropathy. We studied the pathophysiological mechanism of the disease in 2 NEU1-deficient mouse models, a constitutive Neu1-knockout, Neu1ΔEx3, and a conditional phagocyte-specific knockout, Neu1Cx3cr1ΔEx3. Mice of both strains exhibited terminal urinary retention and severe kidney damage with elevated urinary albumin levels, loss of nephrons, renal fibrosis, presence of storage vacuoles, and dysmorphic mitochondria in the intraglomerular and tubular cells. Glycoprotein sialylation in glomeruli, proximal distal tubules, and distal tubules was drastically increased, including that of an endocytic reabsorption receptor megalin. The pool of megalin bearing O-linked glycans with terminal galactose residues, essential for protein targeting and activity, was reduced to below detection levels. Megalin levels were severely reduced, and the protein was directed to lysosomes instead of the apical membrane. Together, our results demonstrated that desialylation by NEU1 plays a crucial role in processing and cellular trafficking of megalin and that NEU1 deficiency in sialidosis impairs megalin-mediated protein reabsorption.
2023-06-27 | Targeting shared molecular etiologies to accelerate drug development for rare diseases
Rare diseases affect over 400 million people worldwide and less than 5% of rare diseases have an approved treatment. Fortunately, the number of underlying disease etiologies is far less than the number of diseases, because many rare diseases share a common molecular etiology. Moreover, many of these shared molecular etiologies are therapeutically actionable. Grouping rare disease patients for clinical trials based on the underlying molecular etiology, rather than the traditional, symptom-based definition of disease, has the potential to greatly increase the number of patients gaining access to clinical trials. Basket clinical trials based on a shared molecular drug target have become common in the field of oncology and have been accepted by regulatory agencies as a basis for drug approvals. Implementation of basket clinical trials in the field of rare diseases is seen by multiple stakeholders-patients, researchers, clinicians, industry, regulators, and funders-as a solution to accelerate the identification of new therapies and address patient's unmet needs.
2022-10-17 | Sialidase Inhibitors with Different Mechanisms
Sialidases, or neuraminidases, are enzymes that catalyze the hydrolysis of sialic acid (Sia)-containing molecules, mostly removal of the terminal Sia (desialylation). By desialylation, sialidase can modulate the functionality of the target compound and is thus often involved in biological pathways. Inhibition of sialidases with inhibitors is an important approach for understanding sialidase function and the underlying mechanisms and could serve as a therapeutic approach as well. Transition-state analogues, such as anti-influenza drugs oseltamivir and zanamivir, are major sialidase inhibitors. In addition, difluoro-sialic acids were developed as mechanism-based sialidase inhibitors. Further, fluorinated quinone methide-based suicide substrates were reported. Sialidase product analogue inhibitors were also explored. Finally, natural products have shown competitive inhibiton against viral, bacterial, and human sialidases. This Perspective describes sialidase inhibitors with different mechanisms and their activities and future potential, which include transition-state analogue inhibitors, mechanism-based inhibitors, suicide substrate inhibitors, product analogue inhibitors, and natural product inhibitors.
gene therapies
2026-04-01 | Lysosomal Neuraminidase 1 (NEU1): Its Unique Molecular Characters and Therapeutic Approaches for Deficiencies.
Neuraminidase 1 (NEU1) is a lysosomal sialidase that removes terminal α-bound sialic acid from sialylglycoconjugates and contributes to ubiquitous catabolism of sialylglycoconjugates and immunoregulatory functions. Different from other human sialidases, including NEU2 to NEU4, NEU1 is first produced as an N-glycosylated precursor protein, which binds to its protective protein/cathepsin A (CTSA) and then forms a lysosomal multienzyme complex (LMC) with β-galactosidase 1 (GLB1) in the rough endoplasmic reticulum (RER) lumen. NEU1 trafficking to lysosomes and intralysosomal activation under acidic pH conditions essentially requires association with CTSA, which carries terminal mannose 6-phosphate (M6P)-type N-glycan to bind with cation-dependent (CD) M6P receptor (CD-M6PR) in the Golgi apparatus via endosomes. In contrast, the single NEU1 gene overexpression in mammalian cells results in NEU1 protein crystallization in the RER owing to self-aggregation at a relatively low intrinsic CTSA level. Two NEU1 deficiencies, sialidosis (SiD) and galactosialidosis (GS), are caused by autosomal recessive NEU1 and CTSA gene mutations, respectively. These untreatable disorders are associated with excessive storage of sialylglycans in neurovisceral organs and systemic symptoms. We produced a new GS model mouse by introducing a homozygous Ctsa IVS6+1g/a mutation into the murine gene locus, leading to partial exon 6 skipping and simultaneous deficiency of Ctsa and Neu1. The GS mice exhibited clinical symptoms similar to those seen in juvenile/adult GS patients, including myoclonic seizures, suppressed behavior, a gargoyle-like face, edema, proctoptosis owing to Neu1 deficiency, and sialylglycan accumulation related to neurovisceral inflammation. Evaluating the efficacy of a novel therapy utilizing GS and SiD model mice and overcoming the human NEU1 gene product shortage will be necessary for a novel, effective treatment for NEU1 deficiencies.
2025-01-25 | Genetic Insights and Clinical Implications of NEU1 Mutations in Sialidosis
Sialidosis is a rare autosomal recessive lysosomal storage disorder caused by mutations in the NEU1 gene, resulting in deficient neuraminidase-1 activity and the subsequent accumulation of sialylated compounds in lysosomes. This review comprehensively analyzes the genetic and clinical heterogeneity associated with sialidosis, emphasizing the distinction between the milder type I form and the more severe type II form. Over 90 pathogenic NEU1 variants, predominantly missense mutations, have been identified, highlighting significant phenotypic diversity. Advancements in genomic sequencing technologies have facilitated the identification of known and novel mutations, with population-specific insights elucidating ethnic variability in symptomatology and genetic profiles. Recent case studies, including a novel compound heterozygous variant, further illustrate the complexity of the genotype–phenotype correlations. Emerging therapeutic approaches, such as enzyme replacement therapy and adeno-associated virus-mediated gene therapy, demonstrate promising potential for restoring neuraminidase-1 function and improving outcomes in preclinical models. This review emphasizes the critical role of genetic analysis in diagnosis and management while advocating for continued research into the molecular mechanisms underlying sialidosis to enable the development of targeted, personalized treatments.
2024-11-28 | Two cases of type I sialidosis and a literature review.
This study aims to compare the clinical and electrophysiological characteristics of two cases of type I sialidosis in Chinese children with those reported in prior literature. The goal is to elucidate the clinical and genetic features of type I sialidosis. Clinical investigations and genetic analyses were conducted on an 11-year-old girl, primarily presenting with short stature, who was admitted in June 2020, and a 10-year-old boy, admitted in July 2023, exhibiting rapid weight gain and accompanying visual impairment as primary manifestations. A literature review was performed by summarizing data from 31 published articles encompassing 69 genetically confirmed cases of type I sialidosis up to 2023 for comparative analysis. Patient 1 exhibited short stature, self-reported poor night vision, a history of occasional febrile seizures, mild scoliosis, bilateral cherry-red spots in the fundus, and prolonged P100 latency in both eyes as observed in visual evoked potentials (VEP). Genetic analysis revealed that she carried compound-heterozygous variants c.239 C > T (p.P80L) and c.880 C > T (p.R294C) in the NEU1 gene, inherited from her parents. Patient 2 presented with rapid weight gain and visual impairment, bilateral cherry-red spots in the fundus, abnormal neuroepithelial layer reflexes in both macular areas, approximately normal P100 latency but severely reduced amplitude in VEP after pupillary dilation, and severe bilateral optic nerve conduction block with relatively normal retinal cell function. Compound-heterozygous variants c.239 C > T (p.P80L) and c.803 A > G (p.T268C) were identified in the NEU1 gene of the Patient 2, inherited from his parents. By combining the cases reported in 31 literature articles with the 2 cases in our study, a total of 71 type I sialidosis patients were analyzed. The most common symptoms observed were muscle spasms (91.5%), followed by ataxia (75%) and seizures (63.6%). Intellectual impairment and abnormal electroencephalograms were more prevalent in Caucasian patients. Additionally, abnormal somatosensory evoked potentials, large cortical waves, and prolonged latency of VEP were more frequently observed in both Asian and Caucasian patients, serving as alternative indicators for early diagnosis. NEU1 gene analysis provides essential guidance for genetic counseling and prenatal diagnosis. The exon 2 variant c.239 C > T (p.P80L) in the NEU1 gene may represent a mutation hotspot among Chinese patients.
2024-11-20 | Lysosomal storage diseases. Mucolipidosis
The epidemiology, clinical, biochemical and molecular genetic characteristics of mucolipidoses — autosomal recessive lysosomal storage diseases that combine the clinical manifestations of mucopolysaccharidoses and sphingolipidoses — are presented. In accordance with the modern classification, types I, II and III mucolipidoses are classified as glycoproteinoses, and type IV mucolipidoses are classified as gangliosidoses. Mucolipidoses type I, or sialidosis, is caused by the presence of inactivating mutations in the α-neuraminidase gene NEU1, and a related disease is galactosialidosis, accompanied by secondary deficiency of α-neuraminidase and β-galactosidase in the CTSA gene of the protective protein cathepsin A. Both diseases are characterized by early progressive delay in psychomotor development, muscle myoclonus, severe ophthalmopathy and early death of patients. The pathogenesis of diseases is associated with excessive accumulation of sialocontaining glycoproteins and oligosaccharides in lysosomes. Hereditary deficiency of N-acetylglucosaminyl-1-phosphotransferase, necessary for the addition of mannose-6-phosphate to the oligosaccharides of lysosomal enzymes, underlies the development of two allelic diseases caused by mutations in the GNPTAB gene mucolipidoses type II, or “I-cell” disease and mucolipidoses type III, alpha/beta or pseudopolydystrophy of Hurler. Mutations in the GNPTG gene, which encodes the gamma subunit of this enzyme, are responsible for the development of the milder type III mucolipidoses (gamma). All these diseases are characterized by impaired phosphorylation and transport of lysosomal enzymes, which is accompanied by severe growth retardation, skeletal abnormalities and early death of patients. Pathogenesis of mucolipidoses type IV, or sialolipidosis, associated with the simultaneous accumulation of phospholipids, sphingolipids, mucopolysaccharides and gangliosides, which occurs as a result of mutations in the MCOLN1 gene, encoding mucolipin 1, which forms a channel localized on the membranes of lysosomes and endosomes, involved in the regulation of lipid and protein transport. The article presents a description of clinical cases of mucolipidosis types II and IIIA. Preclinical trials have shown promise for enzyme replacement therapy, chaperone therapy, and gene therapy for the treatment of sialidosis and galactosialidosis. However, pathogenetic methods of therapy for mucolipidoses have not been described in clinical practice to date.
2024-07-04 | AAV-mediated gene therapy for sialidosis.
Sialidosis (mucolipidosis I) is a glycoprotein storage disease, clinically characterized by a spectrum of systemic and neurological phenotypes. The primary cause of the disease is deficiency of the lysosomal sialidase NEU1, resulting in accumulation of sialylated glycoproteins/oligosaccharides in tissues and body fluids. Neu1-/- mice recapitulate the severe, early-onset forms of the disease, affecting visceral organs, muscles, and the nervous system, with widespread lysosomal vacuolization evident in most cell types. Sialidosis is considered an orphan disorder with no therapy currently available. Here, we assessed the therapeutic potential of AAV-mediated gene therapy for the treatment of sialidosis. Neu1-/- mice were co-injected with two scAAV2/8 vectors, expressing human NEU1 and its chaperone PPCA. Treated mice were phenotypically indistinguishable from their WT controls. NEU1 activity was restored to different extent in most tissues, including the brain, heart, muscle, and visceral organs. This resulted in diminished/absent lysosomal vacuolization in multiple cell types and reversal of sialyl-oligosacchariduria. Lastly, normalization of lysosomal exocytosis in the cerebrospinal fluids and serum of treated mice, coupled to diminished neuroinflammation, were measures of therapeutic efficacy. These findings point to AAV-mediated gene therapy as a suitable treatment for sialidosis and possibly other diseases, associated with low NEU1 expression.
Access all drug discovery papers and probability of success in trials forecasts:
Access all drug discovery papers and probability of success in trials forecasts:
Drug Discovery Landscape
0 orphan drug designations.
0 orphan drug designations.
Let's accelerate rare disease drug discovery
Let's accelerate drug discovery
Get access to Explority AI’s forecasts to outperform average preclinical success rates. Whether you’re expanding your R&D pipeline, evaluating a partnership, or simply have a question — we’d love to hear from you.