RARE DISEASE
Pyridoxal phosphate-responsive seizures
Pyridoxal phosphate-responsive seizures
Pyridoxal phosphate-responsive seizures
Synonyms: PNPO deficiency, PNPO-related neonatal epileptic encephalopathy, Pyridoxal phosphate-dependent seizures, Pyridoxamine 5'-oxidase deficiency, Pyridoxamine 5'-phosphate oxidase deficiency
Synonyms: PNPO deficiency, PNPO-related neonatal epileptic encephalopathy, Pyridoxal phosphate-dependent seizures, Pyridoxamine 5'-oxidase deficiency, Pyridoxamine 5'-phosphate oxidase deficiency
Synonyms: PNPO deficiency, PNPO-related neonatal epileptic encephalopathy, Pyridoxal phosphate-dependent seizures, Pyridoxamine 5'-oxidase deficiency, Pyridoxamine 5'-phosphate oxidase deficiency
Drug discovery
5
drugs
With orphan designations
Overview
Pyridoxal phosphate-responsive seizures (PNPO deficiency) are a rare autosomal recessive disorder caused by PNPO gene mutations, disrupting vitamin B6 metabolism and leading to PLP deficiency. Characterized by neonatal-onset refractory seizures (myoclonus, convulsions) resistant to standard anticonvulsants, it requires lifelong high-dose pyridoxal 5'-phosphate (PLP) or pyridoxine to control seizures. Untreated cases risk fatal encephalopathy, while treated patients often exhibit neurodevelopmental deficits despite seizure reduction [1][2][11].
Categories: rare genetic diseases, rare inborn errors of metabolism, rare neurological diseases
Research Papers
177 drug discovery papers about Pyridoxal phosphate-responsive seizures, with 2 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
177 drug discovery papers about Pyridoxal phosphate-responsive seizures, with 2 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
small molecules
2026-08-04 | Vigabatrin‐Induced Retinal Toxicity: Unraveling the Gamma‐Aminobutyrate–Vitamin B 6 Axis and Metabolic Crosstalk
ABSTRACT Vigabatrin (VGB) is an antiseizure medication used as an add‐on therapy for refractory focal seizures. Despite its clinical efficacy, VGB use is limited by retinal toxicity that may lead to permanent visual loss. This narrative literature review aims to elucidate the emerging molecular and metabolic mechanisms underlying VGB‐induced retinal toxicity, with particular emphasis on the interplay among gamma‐aminobutyrate (GABA) accumulation, taurine depletion, ornithine metabolism dysregulation, and vitamin B 6 ‐dependent pathways to identify potential therapeutic targets for preventing visual impairment. A comprehensive literature search was conducted using PubMed, ScienceDirect, and Google Scholar. Current evidence indicates that VGB‐induced retinal toxicity arises from a complex interplay among GABA accumulation, taurine depletion, taurine transporter modulation, dysregulated ornithine metabolism, and vitamin B 6 –pyridoxal 5′‐phosphate (PLP)‐dependent metabolic alterations. Understanding this complex interplay between GABA–vitamin B 6 axis and metabolic crosstalk offers opportunities for safer therapeutic approaches and potential protective strategies for patients undergoing long‐term VGB therapy. Future research should focus on mechanistic studies, pharmacokinetic profiling, genetic studies, and longitudinal clinical investigations to maximize both seizure control and retinal safety.
2026-04-22 | Should PNPO Deficiency Be Treated In Utero? Clinical Findings From Prenatal Pyridoxine Therapy.
Pyridox(am)ine-5'-phosphate oxidase (PNPO) deficiency is characterized by early-onset epileptic encephalopathy refractory to standard antiseizure medications. It is caused by variants in the PNPO gene, resulting in deficient PNPO enzyme activity, which normally converts pyridoxine-5'-phosphate and pyridoxamine-5'-phosphate (two vitamers of vitamin B6) into the active cofactor, pyridoxal-5'-phosphate (PLP). Treatment relies on PLP or pyridoxine in some cases. Long-term outcomes remain suboptimal. We describe two cases of unrelated children treated with vitamin B6 (pyridoxine) in utero: one with a confirmed prenatal PNPO diagnosis and one at risk due to family history but ultimately unaffected. In utero pyridoxine, combined with early postnatal PLP treatment, allowed excellent seizure control and normal neurodevelopment in the long term. Notably, our first patient, treated from birth, is now 10 years old, representing the oldest reported PNPO-deficient individual treated from birth. Case 2 highlights the safety of prenatal B6 supplementation even in unaffected fetuses. These observations support prenatal pyridoxine supplementation as a safe and potentially beneficial strategy in at-risk PNPO pregnancies.
2026-03-24 | Classical and Emerging Biomarkers in Pyridoxine-Dependent Epilepsy (PDE-ALDH7A1): Implications for Early Diagnosis and Therapeutic Development
Pyridoxine-dependent epilepsy due to ALDH7A1 deficiency (PDE-ALDH7A1) is a rare but treatable epileptic encephalopathy caused by disruption of lysine catabolism and secondary depletion of pyridoxal-5′-phosphate (PLP). Although seizures are often controlled with pyridoxine supplementation, many patients continue to experience neurodevelopmental impairment, underscoring the importance of early diagnosis and improved therapeutic strategies. Central to both diagnosis and pathophysiology is the accumulation of lysine-derived metabolites, most notably α-aminoadipate semialdehyde (α-AASA), its cyclic Schiff base Δ1-piperideine-6-carboxylate (P6C), and pipecolic acid. These metabolites have become the biochemical hallmarks of PDE-ALDH7A1, linking ALDH7A1 pathogenic variants to PLP inactivation and neuronal dysfunction. However, their chemical instability and analytical requirements pose challenges for universal diagnostics and newborn screening. This review summarizes current understanding of lysine catabolism in health and disease, critically evaluates the diagnostic utility and limitations of classical biomarkers, and discusses emerging insights into their pathophysiological roles. We further highlight recent discoveries of novel, chemically stable biomarkers, including 6-oxopiperidine-2-carboxylic acid (6-oxo-PIP), 2-oxopropylpiperidine-2-carboxylic acid (2-OPP), and 6-hydroxy-2-aminocaproic acid (HACA), identified through advanced metabolomics approaches. These metabolites show promise for newborn screening and provide new mechanistic links between metabolic stress, seizure susceptibility, and ongoing neurological morbidity despite pyridoxine treatment. Collectively, advances in biomarker discovery are reshaping diagnostic strategies for PDE-ALDH7A1 and offering new perspectives on disease mechanisms, paving the way for earlier detection and the development of more effective, mechanism-based therapies.
2026-02-27 | Epileptic encephalopathies in inborn errors of metabolism in young children: focus on pyridoxine-dependent epilepsy
Inborn errors of metabolism (IEM) represent one of the most clinically significant yet underdiagnosed causes of epileptic encephalopathies in young children. The team of the Department of Pediatric Neurology at the State Institution "Ukrainian Center of Maternity and Childhood of the NAMS of Ukraine" has been investigating this problem for over 25 years, which served as the foundation for the preparation of this publication. Particular attention is warranted by pyridoxine-dependent epilepsy (PDE) — a rare autosomal recessive disorder caused by pathogenic variants in the ALDH7A1 gene — as a classical example of a treatable metabolic epileptic encephalopathy. Aim - to systematize current evidence on epileptic encephalopathies in inborn errors of metabolism in young children, and to elucidate the underlying pathogenetic mechanisms, clinical features, and approaches to diagnosis and treatment. A systematic review of the scientific literature was conducted using PubMed/MEDLINE and OMIM databases, with a focus on publications from the past 10 years. A clinical case of a 3-month-old girl with neonatal epilepsy refractory to standard therapy is presented. The diagnostic workup included prolonged video-EEG monitoring, brain MRI, biochemical investigations, and next-generation sequencing (NGS) using the CarrierSeq panel (420 genes). Epileptic seizures associated with IEM are characteristically resistant to standard antiseizure medications and may present as status epilepticus at onset. Age of manifestation serves as a key diagnostic indicator: the neonatal period is most typical for pyridoxine-dependent epilepsy, urea cycle defects, and nonketotic hyperglycinemia, while infancy is more characteristic of GLUT1 deficiency, biotinidase deficiency, and peroxisomal disorders. The diagnostic algorithm encompasses three tiers: a basic biochemical panel (glucose, lactate, pyruvate, ammonia, blood gas analysis, plasma amino acids, urine organic acids, acylcarnitine profile), specialized metabolic tests (α-aminoadipic semialdehyde, pipecolic acid, cerebrospinal fluid pyridoxal phosphate level), and molecular genetic analysis. An empirical therapeutic trial with pyridoxine (30 mg/kg/day for 3 days) is indicated in all neonates with seizures of unknown etiology refractory to conventional therapy. In the presented case, two pathogenic variants in compound heterozygous state were identified in the ALDH7A1 gene, confirming the diagnosis of PDE. Targeted therapy comprising pyridoxine, arginine, folinic acid, and a lysine-restricted diet resulted in sustained seizure remission and normalization of psychomotor development. Conclusions. Early identification and verification of a metabolic defect enables pathogenetically targeted treatment with the potential to fundamentally alter the disease prognosis. Nutritional and vitamin-micronutrient therapy represents an effective therapeutic approach for treatable forms of metabolic epilepsy, particularly in pyridoxine-dependent epilepsies. The authors declare no conflict of interest.
2026-01-13 | Liver Transplantation in PNPO Deficiency: Management Challenges and Biological Lessons.
Pyridox(am)ine 5' Phosphate Oxidase deficiency (PNPO) presents with refractory epilepsy responsive to treatment with pyridoxal 5' phosphate (PLP) or pyridoxine. A 15-year-old boy with PNPO deficiency and cirrhosis underwent orthotopic liver transplantation for hepatocellular carcinoma without extra-hepatic disease. Pre-transplant, the boy was cognitively normal with well controlled epilepsy on PLP 50 mg/kg/day. Continuous EEG monitoring was used pre-operatively and post-operatively to identify encephalopathy resulting from PLP deficiency. B6 vitamers (pyridoxine [PN], pyridoxamine [PM], pyridoxal [PL] and phosphorylated forms [PNP, PMP, PLP]) were assayed at times of encephalopathy (symptoms and/or EEG) and for pharmacokinetics. Doses of PLP were titrated to prevent encephalopathy and limit side effects. The intraoperative/immediate postoperative periods were managed with intravenous PLP at a dose which could be reduced to 7.8 mg/kg/day before encephalopathy recurred. Post-transplant, transition to oral PLP (100 mg/kg/day) led to fulminant hepatic impairment, which improved when IV dosing resumed. Subsequent transition to full oral PLP dosing took 9 months with a final dose of 24 mg/kg/day oral PLP. PLP showed dose dependent hepatotoxicity with associated rises in alpha-fetoprotein levels. Gradual PLP dose changes and frequent oral dosing minimised encephalopathy episodes and hepato-toxicity. Six years post-transplant, liver biopsy showed moderate portal fibrosis (Ishak fibrosis stage 2/6, LAFSc score 3/9). Encephalopathy/seizures were associated with lower plasma PL concentrations (40 times above physiological levels); but high plasma PLP concentrations did not prevent encephalopathy. Despite liver transplantation, requirements for supraphysiologic doses of PLP continued, suggesting impaired neuronal PLP salvage is the major factor determining PLP requirements in PNPO deficiency.
oligonucleotides
2025-10-01 | Targeting AASS alleviates neurotoxicity and improves mitochondrial function in astrocyte models for pyridoxine-dependent epilepsy
Pyridoxine-dependent epilepsy (PDE) is a rare neurometabolic disorder of lysine catabolism caused by bi-allelic variants in ALDH7A1. This enzyme deficiency leads to accumulation of neurotoxic metabolites, pyridoxal-phosphate inactivation, and consequently severe neurological symptoms. Current treatments, including vitamin B6 supplementation and lysine-restricted diets, partially alleviate seizures and intellectual disability but are not curative. To explore underlying mechanisms and potential therapies, we generated patient-derived human induced pluripotent stem cell (hiPSC) lines that were subsequently differentiated into astrocytes, the primary source of ALDH7A1 in the brain and key regulators of metabolic homeostasis. Metabolomic analyses confirmed elevated PDE biomarkers, and RNA sequencing revealed gene expression changes consistent with increased oxidative stress. Oxidative damage was validated by markers of DNA oxidation, increased reactive oxygen species (ROS) levels, and lipid peroxidation. In addition, dysregulated oxygen consumption rates suggested mitochondrial dysfunction in PDE astrocytes. Notably, these pathological phenotypes were alleviated by downregulating alpha-aminoadipic semialdehyde synthase (AASS), the first enzyme of the lysine catabolism, by using CRISPR-Cas9 editing or antisense oligonucleotides (AONs). This demonstrates that lysine catabolism underlies these phenotypes and highlights the therapeutic potential of AON therapy targeting AASS to reduce neurotoxic metabolite accumulation. These findings provide a promising strategy for developing targeted treatments for PDE and other rare neurometabolic disorders.
2025-05-12 | Targeting AASS improves neurotoxicity and mitochondrial function in astrocyte models for pyridoxine dependent epilepsy
Abstract Pyridoxine-dependent epilepsy (PDE) is a rare neurometabolic disorder of lysine catabolism caused by bi-allelic variants in ALDH7A1 . This enzyme deficiency leads to the accumulation of neurotoxic metabolites, pyridoxal-phosphate inactivation and consequently severe neurological symptoms. Current treatments, including vitamin B6 supplementation and lysine-restricted diets, partially alleviate seizures and intellectual disability but are not curative. To explore underlying mechanisms and potential therapies, we generated patient-derived human induced pluripotent stem lines (hiPSC) that were subsequently differentiated into astrocytes, the primary source of ALDH7A1 in the brain and key regulators of metabolic homeostasis. Metabolomic analyses confirmed elevated PDE biomarkers, and RNA sequencing revealed gene expression changes consistent with increased oxidative stress. Oxidative damage was validated by markers of DNA oxidation and lipid peroxidation. In addition, dysregulated oxygen consumption rates suggested mitochondrial dysfunction in PDE astrocytes. Notably, these pathological phenotypes were alleviated by downregulating AASS , the first enzyme of the lysine catabolism, by using CRISPR/Cas9 editing or antisense oligonucleotides (AON). This demonstrates that lysine catabolism underlies these phenotypes and highlights the therapeutic potential of AON therapy targeting AASS to reduce neurotoxic metabolite accumulation. These findings provide a promising strategy for developing targeted treatments for PDE and other rare neurometabolic disorders.
2013-01-25 | Clinical, biochemical, and molecular studies in pyridoxine‐dependent epilepsy. Antisense therapy as possible new therapeutic option
Summary Purpose Pyridoxine‐dependent epilepsy seizure ( PDE ; OMIM 266100) is a disorder associated with severe seizures that can be controlled pharmacologically with pyridoxine. In the majority of patients with PDE , the disorder is caused by the deficient activity of the enzyme α‐aminoadipic semialdehyde dehydrogenase (antiquitin protein), which is encoded by the ALDH7A1 gene. The aim of this work was the clinical, biochemical, and genetic analysis of 12 unrelated patients, mostly from S pain, in an attempt to provide further valuable data regarding the wide clinical, biochemical, and genetic spectrum of the disease. Methods The disease was confirmed based on the presence of α‐aminoadipic semialdehyde (α‐ AASA ) in urine measured by liquid chromatography tandem mass spectrometry (LC‐MS/MS) and pipecolic acid ( PA ) in plasma and/or cerebrospinal fluid ( CSF ) measured by high performance liquid chromatography ( HPLC )/ MS / MS and by sequencing analysis of messenger RNA ( mRNA ) and genomic DNA of ALDH7A1 . Key Findings Most of the patients had seizures in the neonatal period, but they responded to vitamin B 6 administration. Three patients developed late‐onset seizures, and most patients showed mild‐to‐moderate postnatal developmental delay. All patients had elevated PA and α‐ AASA levels, even those who had undergone pyridoxine treatment for several years. The clinical spectrum of our patients is not limited to seizures but many of them show associated neurologic dysfunctions such as muscle tone alterations, irritability, and psychomotor retardation. The mutational spectrum of the present patients included 12 mutations, five already reported (c.500 A > G , c.919 C > T , c.1429 G > C c.1217_1218del AT , and c.1482‐1 G > T ) and seven novel sequence changes (c.75 C > T , c.319 G > T , c.554_555del AA , c.757 C > T , c.787 + 1 G > T , c.1474 T > C , c.1093‐?_1620+?). Only one mutation, p. G 477 R (c.1429 G > C ), was recurrent; this was detected in four different alleles. Transcriptional profile analysis of one patient's lymphoblasts and ex vivo splicing analysis showed the silent nucleotide change c.75 C > T to be a novel splicing mutation creating a new donor splice site inside exon 1. Antisense therapy of the aberrant mRNA splicing in a lymphoblast cell line harboring mutation c.75 C > T was successful. Significance The present results broaden our knowledge of PDE , provide information regarding the genetic background of PDE in S pain, afford data of use when making molecular‐based prenatal diagnosis, and provide a cellular proof‐of concept for antisense therapy application.
gene therapies
2025-11-26 | A cell-autonomous role for the vitamin B6 metabolism gene PNPO in Drosophila GABAergic neurons.
In animals, the enzyme pyridox(am)ine 5'-phosphate oxidase (PNPO) is critical for synthesizing the active form of vitamin B6 (VB6), pyridoxal 5'-phosphate (PLP), from inactive vitamers. PLP is a required cofactor for many enzymatic reactions, including the synthesis of GABA and the monoamines. PNPO disruption in humans is associated with an array of epilepsy syndromes, while Drosophila harboring mutations in the sole PNPO ortholog, sugarlethal (sgll), display spontaneous seizures and shortened lifespans. These phenotypes are suppressed by PLP dietary supplementation and are exacerbated by restriction of dietary B6 vitamers. In the context of PNPO deficiency, it remains to be resolved what the specific contributions by cellular subpopulations in the nervous system are to the neurological phenotypes. We addressed this question in sgll mutants by expressing human PNPO (hPNPO) cDNA in cholinergic, glutamatergic, and GABAergic neurons as well as glia and measuring changes in survival and seizure phenotypes. We found hPNPO expression in GABAergic neurons largely restored lifespan and attenuated seizure activity, while glial expression also improved sgll phenotypes albeit to a lesser degree. In contrast, hPNPO expression in either cholinergic or glutamatergic neurons, accounting for most neurons in the fly brain, did not appreciably alter sgll phenotypes. We contrasted these observations with changes in sgll mutants induced by feeding GABA receptor modulators. The GABAB agonist SKF-97541 reduced mortality, while GABA or GABAA receptor modulators did not improve survival. Together, our data establish a cell-autonomous role for PNPO in GABAergic neurons to support brain function, especially under VB6-restricted conditions.
2025-08-11 | A Cell-Autonomous Role for the Vitamin B6 Metabolism Gene PNPO in Drosophila GABAergic Neurons
Abstract In animals, the enzyme pyridox(am)ine 5’-phosphate oxidase (PNPO) is critical for synthesizing the active form of vitamin B6 (VB6), pyridoxal 5’-phosphate (PLP), from inactive vitamers. PLP is a required cofactor for many enzymatic reactions, including the synthesis of GABA and the monoamines. PNPO disruption in humans is associated with an array of epilepsy syndromes, while Drosophila harboring mutations in the sole PNPO ortholog, sugarlethal ( sgll ), display spontaneous seizures and short lifespans. These phenotypes are suppressed by PLP supplementation and are exacerbated by restriction of dietary B6 vitamers. In the context of PNPO deficiency, it remains to be resolved what the specific contributions by cellular subpopulations in the nervous system are to neurological phenotypes. We addressed this question in sgll mutants by expressing human PNPO ( hPNPO ) cDNA in cholinergic, glutamatergic, and GABAergic neurons as well as glia and measuring changes in survival and seizure phenotypes. We found hPNPO expression in GABAergic neurons largely restored lifespan and attenuated seizure activity, while glial expression also improved sgll phenotypes albeit to a lesser degree. In contrast, hPNPO expression in either cholinergic or glutamatergic neurons, accounting for most neurons in the fly brain, did not appreciably alter sgll phenotypes. We contrasted these observations with changes in sgll mutants induced by feeding GABA receptor modulators. The GABA B agonist SKF-97541 reduced mortality, while GABA or GABA A receptor modulators did not improve survival. Together, our data establish a cell-autonomous role for PNPO in GABAergic neurons to support brain function, especially under VB6-restricted conditions.
2019-03-16 | Pyridox(am)ine 5’-phosphate oxidase deficiency induces seizures inDrosophila melanogaster
Abstract Pyridox(am)ine 5’-phosphate oxidase (PNPO) is a rate-limiting enzyme in converting dietary vitamin B6 (VB6) to pyridoxal 5’-phosphate (PLP), the biologically active form of VB6, and involved in the synthesis of neuro-transmitters including GABA, dopamine, and serotonin. In humans, PNPO mutations have been increasingly identified in neonatal epileptic encephalopathy and more recently also in early-onset epilepsy. Till now, little is known about the neurobiological mechanisms underlying PNPO-deficiency-induced seizures due to the lack of animal models. Previously we identified a c.95 C > A missense mutation in sgll - the Drosophila homolog of human PNPO ( hPNPO ) and found mutant ( sgll 95 ) flies exhibiting a lethal phenotype on a diet devoid of VB6. Here we report the establishment of both sgll 95 and ubiquitous sgll knockdown (KD) flies as valid animal models of PNPO-deficiency-induced epilepsy. Both sgll 95 and sgll KD flies exhibit spontaneous seizures before they die. Electrophysiological recordings reveal that seizures caused by PNPO deficiency have characteristics similar to that in flies treated with GABA antagonist picrotoxin. Both seizures and lethality are associated with low PLP levels and can be rescued by ubiquitous expression of wild-type sgll or hPNPO , suggesting the functional conservation of the PNPO enzyme between humans and flies. Results from cell type-specific sgll KD further demonstrate that PNPO in the brain is necessary for seizure prevention and survival. Our establishment of the first animal model of PNPO deficiency will lead to better understanding of VB6 biology, the PNPO gene and its mutations discovered in patients, and can be a cost-effective system to test therapeutic strategies.
small molecules
2026-08-04 | Vigabatrin‐Induced Retinal Toxicity: Unraveling the Gamma‐Aminobutyrate–Vitamin B 6 Axis and Metabolic Crosstalk
ABSTRACT Vigabatrin (VGB) is an antiseizure medication used as an add‐on therapy for refractory focal seizures. Despite its clinical efficacy, VGB use is limited by retinal toxicity that may lead to permanent visual loss. This narrative literature review aims to elucidate the emerging molecular and metabolic mechanisms underlying VGB‐induced retinal toxicity, with particular emphasis on the interplay among gamma‐aminobutyrate (GABA) accumulation, taurine depletion, ornithine metabolism dysregulation, and vitamin B 6 ‐dependent pathways to identify potential therapeutic targets for preventing visual impairment. A comprehensive literature search was conducted using PubMed, ScienceDirect, and Google Scholar. Current evidence indicates that VGB‐induced retinal toxicity arises from a complex interplay among GABA accumulation, taurine depletion, taurine transporter modulation, dysregulated ornithine metabolism, and vitamin B 6 –pyridoxal 5′‐phosphate (PLP)‐dependent metabolic alterations. Understanding this complex interplay between GABA–vitamin B 6 axis and metabolic crosstalk offers opportunities for safer therapeutic approaches and potential protective strategies for patients undergoing long‐term VGB therapy. Future research should focus on mechanistic studies, pharmacokinetic profiling, genetic studies, and longitudinal clinical investigations to maximize both seizure control and retinal safety.
2026-04-22 | Should PNPO Deficiency Be Treated In Utero? Clinical Findings From Prenatal Pyridoxine Therapy.
Pyridox(am)ine-5'-phosphate oxidase (PNPO) deficiency is characterized by early-onset epileptic encephalopathy refractory to standard antiseizure medications. It is caused by variants in the PNPO gene, resulting in deficient PNPO enzyme activity, which normally converts pyridoxine-5'-phosphate and pyridoxamine-5'-phosphate (two vitamers of vitamin B6) into the active cofactor, pyridoxal-5'-phosphate (PLP). Treatment relies on PLP or pyridoxine in some cases. Long-term outcomes remain suboptimal. We describe two cases of unrelated children treated with vitamin B6 (pyridoxine) in utero: one with a confirmed prenatal PNPO diagnosis and one at risk due to family history but ultimately unaffected. In utero pyridoxine, combined with early postnatal PLP treatment, allowed excellent seizure control and normal neurodevelopment in the long term. Notably, our first patient, treated from birth, is now 10 years old, representing the oldest reported PNPO-deficient individual treated from birth. Case 2 highlights the safety of prenatal B6 supplementation even in unaffected fetuses. These observations support prenatal pyridoxine supplementation as a safe and potentially beneficial strategy in at-risk PNPO pregnancies.
2026-03-24 | Classical and Emerging Biomarkers in Pyridoxine-Dependent Epilepsy (PDE-ALDH7A1): Implications for Early Diagnosis and Therapeutic Development
Pyridoxine-dependent epilepsy due to ALDH7A1 deficiency (PDE-ALDH7A1) is a rare but treatable epileptic encephalopathy caused by disruption of lysine catabolism and secondary depletion of pyridoxal-5′-phosphate (PLP). Although seizures are often controlled with pyridoxine supplementation, many patients continue to experience neurodevelopmental impairment, underscoring the importance of early diagnosis and improved therapeutic strategies. Central to both diagnosis and pathophysiology is the accumulation of lysine-derived metabolites, most notably α-aminoadipate semialdehyde (α-AASA), its cyclic Schiff base Δ1-piperideine-6-carboxylate (P6C), and pipecolic acid. These metabolites have become the biochemical hallmarks of PDE-ALDH7A1, linking ALDH7A1 pathogenic variants to PLP inactivation and neuronal dysfunction. However, their chemical instability and analytical requirements pose challenges for universal diagnostics and newborn screening. This review summarizes current understanding of lysine catabolism in health and disease, critically evaluates the diagnostic utility and limitations of classical biomarkers, and discusses emerging insights into their pathophysiological roles. We further highlight recent discoveries of novel, chemically stable biomarkers, including 6-oxopiperidine-2-carboxylic acid (6-oxo-PIP), 2-oxopropylpiperidine-2-carboxylic acid (2-OPP), and 6-hydroxy-2-aminocaproic acid (HACA), identified through advanced metabolomics approaches. These metabolites show promise for newborn screening and provide new mechanistic links between metabolic stress, seizure susceptibility, and ongoing neurological morbidity despite pyridoxine treatment. Collectively, advances in biomarker discovery are reshaping diagnostic strategies for PDE-ALDH7A1 and offering new perspectives on disease mechanisms, paving the way for earlier detection and the development of more effective, mechanism-based therapies.
2026-02-27 | Epileptic encephalopathies in inborn errors of metabolism in young children: focus on pyridoxine-dependent epilepsy
Inborn errors of metabolism (IEM) represent one of the most clinically significant yet underdiagnosed causes of epileptic encephalopathies in young children. The team of the Department of Pediatric Neurology at the State Institution "Ukrainian Center of Maternity and Childhood of the NAMS of Ukraine" has been investigating this problem for over 25 years, which served as the foundation for the preparation of this publication. Particular attention is warranted by pyridoxine-dependent epilepsy (PDE) — a rare autosomal recessive disorder caused by pathogenic variants in the ALDH7A1 gene — as a classical example of a treatable metabolic epileptic encephalopathy. Aim - to systematize current evidence on epileptic encephalopathies in inborn errors of metabolism in young children, and to elucidate the underlying pathogenetic mechanisms, clinical features, and approaches to diagnosis and treatment. A systematic review of the scientific literature was conducted using PubMed/MEDLINE and OMIM databases, with a focus on publications from the past 10 years. A clinical case of a 3-month-old girl with neonatal epilepsy refractory to standard therapy is presented. The diagnostic workup included prolonged video-EEG monitoring, brain MRI, biochemical investigations, and next-generation sequencing (NGS) using the CarrierSeq panel (420 genes). Epileptic seizures associated with IEM are characteristically resistant to standard antiseizure medications and may present as status epilepticus at onset. Age of manifestation serves as a key diagnostic indicator: the neonatal period is most typical for pyridoxine-dependent epilepsy, urea cycle defects, and nonketotic hyperglycinemia, while infancy is more characteristic of GLUT1 deficiency, biotinidase deficiency, and peroxisomal disorders. The diagnostic algorithm encompasses three tiers: a basic biochemical panel (glucose, lactate, pyruvate, ammonia, blood gas analysis, plasma amino acids, urine organic acids, acylcarnitine profile), specialized metabolic tests (α-aminoadipic semialdehyde, pipecolic acid, cerebrospinal fluid pyridoxal phosphate level), and molecular genetic analysis. An empirical therapeutic trial with pyridoxine (30 mg/kg/day for 3 days) is indicated in all neonates with seizures of unknown etiology refractory to conventional therapy. In the presented case, two pathogenic variants in compound heterozygous state were identified in the ALDH7A1 gene, confirming the diagnosis of PDE. Targeted therapy comprising pyridoxine, arginine, folinic acid, and a lysine-restricted diet resulted in sustained seizure remission and normalization of psychomotor development. Conclusions. Early identification and verification of a metabolic defect enables pathogenetically targeted treatment with the potential to fundamentally alter the disease prognosis. Nutritional and vitamin-micronutrient therapy represents an effective therapeutic approach for treatable forms of metabolic epilepsy, particularly in pyridoxine-dependent epilepsies. The authors declare no conflict of interest.
2026-01-13 | Liver Transplantation in PNPO Deficiency: Management Challenges and Biological Lessons.
Pyridox(am)ine 5' Phosphate Oxidase deficiency (PNPO) presents with refractory epilepsy responsive to treatment with pyridoxal 5' phosphate (PLP) or pyridoxine. A 15-year-old boy with PNPO deficiency and cirrhosis underwent orthotopic liver transplantation for hepatocellular carcinoma without extra-hepatic disease. Pre-transplant, the boy was cognitively normal with well controlled epilepsy on PLP 50 mg/kg/day. Continuous EEG monitoring was used pre-operatively and post-operatively to identify encephalopathy resulting from PLP deficiency. B6 vitamers (pyridoxine [PN], pyridoxamine [PM], pyridoxal [PL] and phosphorylated forms [PNP, PMP, PLP]) were assayed at times of encephalopathy (symptoms and/or EEG) and for pharmacokinetics. Doses of PLP were titrated to prevent encephalopathy and limit side effects. The intraoperative/immediate postoperative periods were managed with intravenous PLP at a dose which could be reduced to 7.8 mg/kg/day before encephalopathy recurred. Post-transplant, transition to oral PLP (100 mg/kg/day) led to fulminant hepatic impairment, which improved when IV dosing resumed. Subsequent transition to full oral PLP dosing took 9 months with a final dose of 24 mg/kg/day oral PLP. PLP showed dose dependent hepatotoxicity with associated rises in alpha-fetoprotein levels. Gradual PLP dose changes and frequent oral dosing minimised encephalopathy episodes and hepato-toxicity. Six years post-transplant, liver biopsy showed moderate portal fibrosis (Ishak fibrosis stage 2/6, LAFSc score 3/9). Encephalopathy/seizures were associated with lower plasma PL concentrations (40 times above physiological levels); but high plasma PLP concentrations did not prevent encephalopathy. Despite liver transplantation, requirements for supraphysiologic doses of PLP continued, suggesting impaired neuronal PLP salvage is the major factor determining PLP requirements in PNPO deficiency.
oligonucleotides
2025-10-01 | Targeting AASS alleviates neurotoxicity and improves mitochondrial function in astrocyte models for pyridoxine-dependent epilepsy
Pyridoxine-dependent epilepsy (PDE) is a rare neurometabolic disorder of lysine catabolism caused by bi-allelic variants in ALDH7A1. This enzyme deficiency leads to accumulation of neurotoxic metabolites, pyridoxal-phosphate inactivation, and consequently severe neurological symptoms. Current treatments, including vitamin B6 supplementation and lysine-restricted diets, partially alleviate seizures and intellectual disability but are not curative. To explore underlying mechanisms and potential therapies, we generated patient-derived human induced pluripotent stem cell (hiPSC) lines that were subsequently differentiated into astrocytes, the primary source of ALDH7A1 in the brain and key regulators of metabolic homeostasis. Metabolomic analyses confirmed elevated PDE biomarkers, and RNA sequencing revealed gene expression changes consistent with increased oxidative stress. Oxidative damage was validated by markers of DNA oxidation, increased reactive oxygen species (ROS) levels, and lipid peroxidation. In addition, dysregulated oxygen consumption rates suggested mitochondrial dysfunction in PDE astrocytes. Notably, these pathological phenotypes were alleviated by downregulating alpha-aminoadipic semialdehyde synthase (AASS), the first enzyme of the lysine catabolism, by using CRISPR-Cas9 editing or antisense oligonucleotides (AONs). This demonstrates that lysine catabolism underlies these phenotypes and highlights the therapeutic potential of AON therapy targeting AASS to reduce neurotoxic metabolite accumulation. These findings provide a promising strategy for developing targeted treatments for PDE and other rare neurometabolic disorders.
2025-05-12 | Targeting AASS improves neurotoxicity and mitochondrial function in astrocyte models for pyridoxine dependent epilepsy
Abstract Pyridoxine-dependent epilepsy (PDE) is a rare neurometabolic disorder of lysine catabolism caused by bi-allelic variants in ALDH7A1 . This enzyme deficiency leads to the accumulation of neurotoxic metabolites, pyridoxal-phosphate inactivation and consequently severe neurological symptoms. Current treatments, including vitamin B6 supplementation and lysine-restricted diets, partially alleviate seizures and intellectual disability but are not curative. To explore underlying mechanisms and potential therapies, we generated patient-derived human induced pluripotent stem lines (hiPSC) that were subsequently differentiated into astrocytes, the primary source of ALDH7A1 in the brain and key regulators of metabolic homeostasis. Metabolomic analyses confirmed elevated PDE biomarkers, and RNA sequencing revealed gene expression changes consistent with increased oxidative stress. Oxidative damage was validated by markers of DNA oxidation and lipid peroxidation. In addition, dysregulated oxygen consumption rates suggested mitochondrial dysfunction in PDE astrocytes. Notably, these pathological phenotypes were alleviated by downregulating AASS , the first enzyme of the lysine catabolism, by using CRISPR/Cas9 editing or antisense oligonucleotides (AON). This demonstrates that lysine catabolism underlies these phenotypes and highlights the therapeutic potential of AON therapy targeting AASS to reduce neurotoxic metabolite accumulation. These findings provide a promising strategy for developing targeted treatments for PDE and other rare neurometabolic disorders.
2013-01-25 | Clinical, biochemical, and molecular studies in pyridoxine‐dependent epilepsy. Antisense therapy as possible new therapeutic option
Summary Purpose Pyridoxine‐dependent epilepsy seizure ( PDE ; OMIM 266100) is a disorder associated with severe seizures that can be controlled pharmacologically with pyridoxine. In the majority of patients with PDE , the disorder is caused by the deficient activity of the enzyme α‐aminoadipic semialdehyde dehydrogenase (antiquitin protein), which is encoded by the ALDH7A1 gene. The aim of this work was the clinical, biochemical, and genetic analysis of 12 unrelated patients, mostly from S pain, in an attempt to provide further valuable data regarding the wide clinical, biochemical, and genetic spectrum of the disease. Methods The disease was confirmed based on the presence of α‐aminoadipic semialdehyde (α‐ AASA ) in urine measured by liquid chromatography tandem mass spectrometry (LC‐MS/MS) and pipecolic acid ( PA ) in plasma and/or cerebrospinal fluid ( CSF ) measured by high performance liquid chromatography ( HPLC )/ MS / MS and by sequencing analysis of messenger RNA ( mRNA ) and genomic DNA of ALDH7A1 . Key Findings Most of the patients had seizures in the neonatal period, but they responded to vitamin B 6 administration. Three patients developed late‐onset seizures, and most patients showed mild‐to‐moderate postnatal developmental delay. All patients had elevated PA and α‐ AASA levels, even those who had undergone pyridoxine treatment for several years. The clinical spectrum of our patients is not limited to seizures but many of them show associated neurologic dysfunctions such as muscle tone alterations, irritability, and psychomotor retardation. The mutational spectrum of the present patients included 12 mutations, five already reported (c.500 A > G , c.919 C > T , c.1429 G > C c.1217_1218del AT , and c.1482‐1 G > T ) and seven novel sequence changes (c.75 C > T , c.319 G > T , c.554_555del AA , c.757 C > T , c.787 + 1 G > T , c.1474 T > C , c.1093‐?_1620+?). Only one mutation, p. G 477 R (c.1429 G > C ), was recurrent; this was detected in four different alleles. Transcriptional profile analysis of one patient's lymphoblasts and ex vivo splicing analysis showed the silent nucleotide change c.75 C > T to be a novel splicing mutation creating a new donor splice site inside exon 1. Antisense therapy of the aberrant mRNA splicing in a lymphoblast cell line harboring mutation c.75 C > T was successful. Significance The present results broaden our knowledge of PDE , provide information regarding the genetic background of PDE in S pain, afford data of use when making molecular‐based prenatal diagnosis, and provide a cellular proof‐of concept for antisense therapy application.
gene therapies
2025-11-26 | A cell-autonomous role for the vitamin B6 metabolism gene PNPO in Drosophila GABAergic neurons.
In animals, the enzyme pyridox(am)ine 5'-phosphate oxidase (PNPO) is critical for synthesizing the active form of vitamin B6 (VB6), pyridoxal 5'-phosphate (PLP), from inactive vitamers. PLP is a required cofactor for many enzymatic reactions, including the synthesis of GABA and the monoamines. PNPO disruption in humans is associated with an array of epilepsy syndromes, while Drosophila harboring mutations in the sole PNPO ortholog, sugarlethal (sgll), display spontaneous seizures and shortened lifespans. These phenotypes are suppressed by PLP dietary supplementation and are exacerbated by restriction of dietary B6 vitamers. In the context of PNPO deficiency, it remains to be resolved what the specific contributions by cellular subpopulations in the nervous system are to the neurological phenotypes. We addressed this question in sgll mutants by expressing human PNPO (hPNPO) cDNA in cholinergic, glutamatergic, and GABAergic neurons as well as glia and measuring changes in survival and seizure phenotypes. We found hPNPO expression in GABAergic neurons largely restored lifespan and attenuated seizure activity, while glial expression also improved sgll phenotypes albeit to a lesser degree. In contrast, hPNPO expression in either cholinergic or glutamatergic neurons, accounting for most neurons in the fly brain, did not appreciably alter sgll phenotypes. We contrasted these observations with changes in sgll mutants induced by feeding GABA receptor modulators. The GABAB agonist SKF-97541 reduced mortality, while GABA or GABAA receptor modulators did not improve survival. Together, our data establish a cell-autonomous role for PNPO in GABAergic neurons to support brain function, especially under VB6-restricted conditions.
2025-08-11 | A Cell-Autonomous Role for the Vitamin B6 Metabolism Gene PNPO in Drosophila GABAergic Neurons
Abstract In animals, the enzyme pyridox(am)ine 5’-phosphate oxidase (PNPO) is critical for synthesizing the active form of vitamin B6 (VB6), pyridoxal 5’-phosphate (PLP), from inactive vitamers. PLP is a required cofactor for many enzymatic reactions, including the synthesis of GABA and the monoamines. PNPO disruption in humans is associated with an array of epilepsy syndromes, while Drosophila harboring mutations in the sole PNPO ortholog, sugarlethal ( sgll ), display spontaneous seizures and short lifespans. These phenotypes are suppressed by PLP supplementation and are exacerbated by restriction of dietary B6 vitamers. In the context of PNPO deficiency, it remains to be resolved what the specific contributions by cellular subpopulations in the nervous system are to neurological phenotypes. We addressed this question in sgll mutants by expressing human PNPO ( hPNPO ) cDNA in cholinergic, glutamatergic, and GABAergic neurons as well as glia and measuring changes in survival and seizure phenotypes. We found hPNPO expression in GABAergic neurons largely restored lifespan and attenuated seizure activity, while glial expression also improved sgll phenotypes albeit to a lesser degree. In contrast, hPNPO expression in either cholinergic or glutamatergic neurons, accounting for most neurons in the fly brain, did not appreciably alter sgll phenotypes. We contrasted these observations with changes in sgll mutants induced by feeding GABA receptor modulators. The GABA B agonist SKF-97541 reduced mortality, while GABA or GABA A receptor modulators did not improve survival. Together, our data establish a cell-autonomous role for PNPO in GABAergic neurons to support brain function, especially under VB6-restricted conditions.
2019-03-16 | Pyridox(am)ine 5’-phosphate oxidase deficiency induces seizures inDrosophila melanogaster
Abstract Pyridox(am)ine 5’-phosphate oxidase (PNPO) is a rate-limiting enzyme in converting dietary vitamin B6 (VB6) to pyridoxal 5’-phosphate (PLP), the biologically active form of VB6, and involved in the synthesis of neuro-transmitters including GABA, dopamine, and serotonin. In humans, PNPO mutations have been increasingly identified in neonatal epileptic encephalopathy and more recently also in early-onset epilepsy. Till now, little is known about the neurobiological mechanisms underlying PNPO-deficiency-induced seizures due to the lack of animal models. Previously we identified a c.95 C > A missense mutation in sgll - the Drosophila homolog of human PNPO ( hPNPO ) and found mutant ( sgll 95 ) flies exhibiting a lethal phenotype on a diet devoid of VB6. Here we report the establishment of both sgll 95 and ubiquitous sgll knockdown (KD) flies as valid animal models of PNPO-deficiency-induced epilepsy. Both sgll 95 and sgll KD flies exhibit spontaneous seizures before they die. Electrophysiological recordings reveal that seizures caused by PNPO deficiency have characteristics similar to that in flies treated with GABA antagonist picrotoxin. Both seizures and lethality are associated with low PLP levels and can be rescued by ubiquitous expression of wild-type sgll or hPNPO , suggesting the functional conservation of the PNPO enzyme between humans and flies. Results from cell type-specific sgll KD further demonstrate that PNPO in the brain is necessary for seizure prevention and survival. Our establishment of the first animal model of PNPO deficiency will lead to better understanding of VB6 biology, the PNPO gene and its mutations discovered in patients, and can be a cost-effective system to test therapeutic strategies.
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
5 orphan drug designations for Pyridoxal phosphate-responsive seizures.
5 orphan drug designations for Pyridoxal phosphate-responsive seizures.
Drug | Therapy type | Orphan designation | Clinical trial status | Sponsor |
|---|---|---|---|---|
Pyridoxal 5'-phosphate | small molecules | EMA | — | Amsterdam UMC |
Pyridoxal 5'-phosphate | small molecules | EMA | — | Amsterdam UMC |
Pyridoxal 5'-phosphate | small molecules | EMA | Medicure Pharma Europe Limited | |
pyridoxal-5¿ phosphate monohydrate (P5P) | small molecules | FDA | Medicure International Inc. | |
Pyridoxal 5'-phosphate | small molecules | EMA | — | Great Ormond Street Hospital for Children, NHS Foundation Trust |
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.