Pyridoxine responsiveness in novel mutations of the PNPO gene

Patient mutations in DRP1 perturb synaptic maturation of cortical neurons

With the advent of exome sequencing, a growing number of children are being identified with de novo loss of function mutations in the dynamin 1 like (DNM1L) gene encoding the large GTPase essential for mitochondrial fission, dynamin-related protein 1 (DRP1); these mutations result in severe neurodevelopmental phenotypes, such as developmental delay, optic atrophy, and epileptic encephalopathies. Though it is established that mitochondrial fission is an essential precursor to the rapidly changing metabolic needs of the developing cortex, it is not understood how identified mutations in different domains of DRP1 uniquely disrupt cortical development and synaptic maturation. We leveraged the power of induced pluripotent stem cells (iPSCs) harboring DRP1 mutations in either the GTPase or stalk domains to model early stages of cortical development in vitro. High-resolution time-lapse imaging of axonal transport in mutant DRP1 cortical neurons reveals mutation-specific changes in mitochondrial motility of severely hyperfused mitochondrial structures. Transcriptional profiling of mutant DRP1 cortical neurons during maturation also implicates mutation dependent alterations in synaptic development and calcium regulation gene expression. Disruptions in calcium dynamics were confirmed using live functional recordings of 100 DIV (days in vitro) mutant DRP1 cortical neurons. These findings and deficits in pre- and post-synaptic marker colocalization using super resolution microscopy, strongly suggest that altered mitochondrial morphology of DRP1 mutant neurons leads to pathogenic dysregulation of synaptic development and activity.

Utility and limitations of EEG in the diagnosis and management of ALDH7A1-related pyridoxine-dependent epilepsy. A retrospective observational study

Purpose

Pyridoxine-dependent epilepsy due to ALDH7A1 variants (PDE-ALDH7A1) is a rare disorder, presenting typically with severe neonatal, epileptic encephalopathy. Early diagnosis is imperative to prevent uncontrolled seizures. We have explored the role of EEG in the diagnosis and management of PDE.

Methods

A total of 13 Norwegian patients with PDE-ALDH7A1 were identified, of whom five had reached adult age. Altogether 163 EEG recordings were assessed, 101 from the 1st year of life.

Results

Median age at seizure onset was 9 h (IQR 41), range 1 h-6 days. Median delay from first seizure to first pyridoxine injection was 2 days (IQR 5.5). An EEG burst suppression pattern was seen in eight patients (62%) during the first 5 days of life. Eleven patients had recordings during pyridoxine injections: in three, immediate EEG improvement correlated with seizure control, whereas in six, no change of epileptiform activity occurred. Of these six, one had prompt clinical effect, one had delayed effect (< 1 day), one had no effect, one had uncertain effect, and another had more seizures. A patient without seizures at time of pyridoxine trial remained seizure free for 6 days. Two patients with prompt clinical effect had increased paroxysmal activity, one as a conversion to burst suppression. Autonomic seizures in the form of apnoea appeared to promote respiratory distress and were documented by EEG in one patient. EEG follow-up in adult age did not show signs of progressing encephalopathy.

Conclusion

A neonatal burst suppression EEG pattern should raise the suspicion of PDE-ALDH7A1. Respiratory distress is common; isolated apnoeic seizures may contribute. EEG responses during pyridoxine trials are diverse, often with poor correlation to immediate clinical effect. Reliance on single trials may lead to under-recognition of this treatable condition. Pyridoxine should be continued until results from biomarkers and genetic testing are available.

Treatment of seizures in the neonate: Guidelines and consensus-based recommendations-Special report from the ILAE Task Force on Neonatal Seizures

Seizures are common in neonates, but there is substantial management variability. The Neonatal Task Force of the International League Against Epilepsy (ILAE) developed evidence-based recommendations about antiseizure medication (ASM) management in neonates in accordance with ILAE standards. Six priority questions were formulated, a systematic literature review and meta-analysis were performed, and results were reported following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 standards. Bias was evaluated using the Cochrane tool and risk of Bias in non-randomised studies - of interventions (ROBINS-I), and quality of evidence was evaluated using grading of recommendations, assessment, development and evaluation (GRADE). If insufficient evidence was available, then expert opinion was sought using Delphi consensus methodology. The strength of recommendations was defined according to the ILAE Clinical Practice Guidelines development tool. There were six main recommendations. First, phenobarbital should be the first-line ASM (evidence-based recommendation) regardless of etiology (expert agreement), unless channelopathy is likely the cause for seizures (e.g., due to family history), in which case phenytoin or carbamazepine should be used. Second, among neonates with seizures not responding to first-line ASM, phenytoin, levetiracetam, midazolam, or lidocaine may be used as a second-line ASM (expert agreement). In neonates with cardiac disorders, levetiracetam may be the preferred second-line ASM (expert agreement). Third, following cessation of acute provoked seizures without evidence for neonatal-onset epilepsy, ASMs should be discontinued before discharge home, regardless of magnetic resonance imaging or electroencephalographic findings (expert agreement). Fourth, therapeutic hypothermia may reduce seizure burden in neonates with hypoxic-ischemic encephalopathy (evidence-based recommendation). Fifth, treating neonatal seizures (including electrographic-only seizures) to achieve a lower seizure burden may be associated with improved outcome (expert agreement). Sixth, a trial of pyridoxine may be attempted in neonates presenting with clinical features of vitamin B6-dependent epilepsy and seizures unresponsive to second-line ASM (expert agreement). Additional considerations include a standardized pathway for the management of neonatal seizures in each neonatal unit and informing parents/guardians about the diagnosis of seizures and initial treatment options.

On pathways and blind alleys-The importance of biomarkers in vitamin B6 -dependent epilepsies

Over the past two decades, the field of vitamin B6 -dependent epilepsies has evolved by the recognition of a growing number of gene defects (ALDH7A1, PNPO, ALPL, ALDH4A1, PLPBP as well as defects of the glycosylphosphatidylinositol anchor proteins) that all lead to reduced availability of pyridoxal 5'-phosphate, an important cofactor in neurotransmitter and amino acid metabolism. In addition, positive pyridoxine response has been observed in other monogenic defects such as MOCS2 deficiency or KCNQ2 and there may be more defects to be discovered. Most entities lead to neonatal onset pharmaco-resistant myoclonic seizures or even status epilepticus and pose an emergency to the treating physician. Research has unraveled specific biomarkers for several of these entities (PNPO deficiency, ALDH7A1 deficiency, ALDH4A1 deficiency, ALPL deficiency causing congenital hypophosphatasia and glycosylphosphatidylinositol anchoring defects with hyperphosphatasia), that can be detected in plasma or urine, while there is no biomarker to test for PLPHP deficiency. Secondary elevation of glycine or lactate was recognized as diagnostic pitfall. An algorithm for a standardized trial with vitamin B6 should be in place in every newborn unit in order not to miss these well-treatable inborn errors of metabolism. The Komrower lecture of 2022 provided me with the opportunity to tell the story about the conundrums of research into vitamin B6 -dependent epilepsies that kept some surprises and many novel insights into pathomechanisms of vitamin metabolism. Every single step had benefits for the patients and families that we care for and advocates for a close collaboration of clinician scientists with basic research.

Epilepsy Phenotypes of Vitamin B6-Dependent Diseases: An Updated Systematic Review

Background: Vitamin B6-dependent epilepsies include treatable diseases responding to pyridoxine or pyridoxal-5Iphosphate (ALDH7A1 deficiency, PNPO deficiency, PLP binding protein deficiency, hyperprolinemia type II and hypophosphatasia and glycosylphosphatidylinositol anchor synthesis defects). Patients and methods: We conducted a systematic review of published pediatric cases with a confirmed molecular genetic diagnosis of vitamin B6-dependent epilepsy according to PRISMA guidelines. Data on demographic features, seizure semiology, EEG patterns, neuroimaging, treatment, and developmental outcomes were collected. Results: 497 published patients fulfilled the inclusion criteria. Seizure onset manifested at 59.8 ± 291.6 days (67.8% of cases in the first month of life). Clonic, tonic-clonic, and myoclonic seizures accounted for two-thirds of the cases, while epileptic spasms were observed in 7.6%. Burst-suppression/suppression-burst represented the most frequently reported specific EEG pattern (14.4%), mainly in PLPB, ALDH7A1, and PNPO deficiency. Pyridoxine was administered to 312 patients (18.5% intravenously, 76.9% orally, 4.6% not specified), and 180 also received antiseizure medications. Pyridoxine dosage ranged between 1 and 55 mg/kg/die. Complete seizure freedom was achieved in 160 patients, while a significant seizure reduction occurred in 38. PLP, lysine-restricted diet, and arginine supplementation were used in a small proportion of patients with variable efficacy. Global developmental delay was established in 30.5% of a few patients in whom neurocognitive tests were performed. Conclusions: Despite the wide variability, the most frequent hallmarks of the epilepsy phenotype in patients with vitamin B6-dependent seizures include generalized or focal motor seizure semiology and a burst suppression/suppression burst pattern in EEG.

Role of vitamins in epilepsy

Epilepsy is a chronic neurological disorder that presents as recurrent, unprovoked seizures. Pharmacotherapy is the main treatment for epilepsy, but at least 30% of patients with epilepsy have pharmacoresistant epilepsy. Therefore, non-pharmacological treatments are still required. In addition to electrophysiological aberrations contributing to epileptogenesis and pathophysiology in epilepsy, neuroinflammation, oxidative stress, and metabolic derangement have been investigated as drug targets in the treatment of epilepsy. Vitamins have antioxidant, anti-inflammatory, and immunomodulatory effects, which can be beneficial for the treatment of epilepsy. Herein, we comprehensively review the role of vitamins in epilepsy. Certain epilepsies are vitamin-dependent or vitamin-responsive. Most studies on vitamins in epilepsy are of low evidence level or limited to animal studies. Nevertheless, vitamin supplementation should be considered in epilepsy therapy. Additionally, certain anti-seizure medications may alter the serum levels of certain vitamins. Monitoring the serum levels of vitamins and supplementing vitamins when needed are suggested during the follow-up of patients with epilepsy.

Precision Medicine Approaches for Infantile-Onset Developmental and Epileptic Encephalopathies

Epilepsy is an etiologically heterogeneous condition; however, genetic factors are thought to play a role in most patients. For those with infantile-onset developmental and epileptic encephalopathy (DEE), a genetic diagnosis is now obtained in more than 50% of patients. There is considerable motivation to utilize these molecular diagnostic data to help guide treatment, as children with DEEs often have drug-resistant seizures as well as developmental impairment related to cerebral epileptiform activity. Precision medicine approaches have the potential to dramatically improve the quality of life for these children and their families. At present, treatment can be targeted for patients with diagnoses in many genetic causes of infantile-onset DEE, including genes encoding sodium or potassium channel subunits, tuberous sclerosis, and congenital metabolic diseases. Precision medicine may refer to more intelligent choices of conventional antiseizure medications, repurposed agents previously used for other indications, novel compounds, enzyme replacement, or gene therapy approaches. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Complexities of pyridoxine response in PNPO deficiency

Pyridox(am)ine- 5- phosphate Oxidase deficiency (PNPO) is a rare cause of neonatal metabolic encephalopathy associated with refractory status epilepticus. We report a case of a premature neonate presenting with drug-resistant seizures beginning at 2 hours of life. The baby showed initial transient response to pyridoxine followed by recurrence. Genetic report confirmed the diagnosis of PNPO deficiency. A literature review on phenotypic variants in terms of response to pyridoxine is also presented along with a proposed algorithm to manage a case of suspected vitamin responsive epilepsy. This case highlights our limited understanding of why variation in response to treatment exists in children with PNPO deficiency.

Inborn errors in the vitamin B6 salvage enzymes associated with neonatal epileptic encephalopathy and other pathologies

Pyridoxal 5'-phosphate (PLP), the active cofactor form of vitamin B6 is required by over 160 PLP-dependent (vitamin B6) enzymes serving diverse biological roles, such as carbohydrates, amino acids, hemes, and neurotransmitters metabolism. Three key enzymes, pyridoxal kinase (PL kinase), pyridoxine 5'-phosphate oxidase (PNPO), and phosphatases metabolize and supply PLP to PLP-dependent enzymes through the salvage pathway. In born errors in the salvage enzymes are known to cause inadequate levels of PLP in the cell, particularly in neuronal cells. The resulting PLP deficiency is known to cause or implicated in several pathologies, most notably seizures. One such disorder, PNPO-dependent neonatal epileptic encephalopathy (NEE) results from natural mutations in PNPO and leads to null or reduced enzymatic activity. NEE does not respond to conventional antiepileptic drugs but may respond to treatment with the B6 vitamers PLP and/or pyridoxine (PN). In born errors that lead to PLP deficiency in cells have also been reported in PL kinase, however, to date none has been associated with epilepsy or seizure. One such pathology is polyneuropathy that responds to PLP therapy. Phosphatase deficiency or hypophosphatasia disorder due to pathogenic mutations in alkaline phosphatase is known to cause seizures that respond to PN therapy. In this article, we review the biochemical features of in born errors pertaining to the salvage enzyme's deficiency that leads to NEE and other pathologies. We also present perspective on vitamin B6 treatment for these disorders, along with attempts to develop zebrafish model to study the NEE syndrome in vivo.

West Syndrome Is an Exceptional Presentation of Pyridoxine- and Pyridoxal Phosphate-Dependent Epilepsy: Data From a French Cohort and Review of the Literature

Objective: To characterize the electro-clinical presentation of patients with pyridoxine-dependent epilepsy (PDE) and pyridoxal phosphate (PLP)-dependent epilepsy in order to determine whether some of them could be diagnosed as de novo West syndrome, i. e., West syndrome that starts after the age of 2 months without other types of seizures (focal seizures for instance) before the onset of epileptic spasms. Methods: We analyzed data from an unpublished cohort of 28 genetically confirmed cases of PDE with antiquitine (ATQ) deficiency and performed a review of the literature looking for description of West syndrome in patients with either PDE with ATQ deficiency or PLP-dependent epilepsy with Pyridox(am)ine phosphate oxidase (PNPO) deficiency. Results: Of the 28 cases from the ATQ deficiency French cohort, 5 had spasms. In four cases, spasms were associated with other types of seizures (myoclonus, focal seizures). In the last case, seizures started on the day of birth. None of these cases corresponded to de novo West syndrome. The review of the literature found only one case of PNPO deficiency presenting as de novo West syndrome and no case of ATQ deficiency. Significance: The presentation of PDE- and PLP-dependent epilepsy as de novo West syndrome is so exceptional that it probably does not justify a systematic trial of pyridoxine or PLP. We propose considering a therapeutic trial with these vitamins in West syndrome if spasms are associated with other seizure types or start before the age of 2 months.

A Proposed Diagnostic Algorithm for Inborn Errors of Metabolism Presenting With Movements Disorders

Inherited metabolic diseases or inborn errors of metabolism frequently manifest with both hyperkinetic (dystonia, chorea, myoclonus, ataxia, tremor, etc.) and hypokinetic (rigid-akinetic syndrome) movement disorders. The diagnosis of these diseases is in many cases difficult, because the same movement disorder can be caused by several diseases. Through a literature review, two hundred and thirty one inborn errors of metabolism presenting with movement disorders have been identified. Fifty-one percent of these diseases exhibits two or more movement disorders, of which ataxia and dystonia are the most frequent. Taking into account the wide range of these disorders, a methodical evaluation system needs to be stablished. This work proposes a six-step diagnostic algorithm for the identification of inborn errors of metabolism presenting with movement disorders comprising red flags, characterization of the movement disorders phenotype (type of movement disorder, age and nature of onset, distribution and temporal pattern) and other neurological and non-neurological signs, minimal biochemical investigation to diagnose treatable diseases, radiological patterns, genetic testing and ultimately, symptomatic, and disease-specific treatment. As a strong action, it is emphasized not to miss any treatable inborn error of metabolism through the algorithm.

The role of clinical response to treatment in determining pathogenicity of genomic variants

PURPOSE

The 2015 American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines for the interpretation of sequence variants provide a framework to standardize terminology in the classification of variants uncovered through genetic testing. We aimed to assess the validity of utilizing clinical response to therapies specifically targeted to a suspected disease in clarifying variant pathogenicity.

METHODS

Five families with disparate clinical presentations and different genetic diseases evaluated and treated in multiple diagnostic settings are summarized.

RESULTS

Extended evaluations indicated possible genetic diagnoses and assigned candidate causal variants, but the cumulative clinical, biochemical, and molecular information in each instance was not completely consistent with the identified disease. Initiation of treatment specific to the suspected diagnoses in the affected individuals led to clinical improvement in all five families.

CONCLUSION

We propose that the effect of therapies that are specific and targeted to treatable genetic diseases embodies an in vivo physiological response and could be considered as additional criteria within the 2015 ACMG/AMP guidelines in determining genomic variant pathogenicity.

Phenotypic and molecular spectrum of pyridoxamine-5'-phosphate oxidase deficiency: A scoping review of 87 cases of pyridoxamine-5'-phosphate oxidase deficiency

Pyridoxamine-5'-phosphate oxidase (PNPO) deficiency is an autosomal recessive pyridoxal 5'-phosphate (PLP)-vitamin-responsive epileptic encephalopathy. The emerging feature of PNPO deficiency is the occurrence of refractory seizures in the first year of life. Pre-maturity and fetal distress, combined with neonatal seizures, are other associated key characteristics. The phenotype results from a dependency of PLP which regulates several enzymes in the body. We present the phenotypic and genotypic spectrum of (PNPO) deficiency based on a literature review (2002-2020) of reports (n = 33) of patients with confirmed PNPO deficiency (n = 87). All patients who received PLP (n = 36) showed a clinical response, with a complete dramatic PLP response with seizure cessation observed in 61% of patients. In spite of effective seizure control with PLP, approximately 56% of patients affected with PLP-dependent epilepsy suffer developmental delay/intellectual disability. There is no diagnostic biomarker, and molecular testing required for diagnosis. However, we noted that cerebrospinal fluid (CSF) PLP was low in 81%, CSF glycine was high in 80% and urinary vanillactic acid was high in 91% of the cases. We observed only a weak correlation between the severity of PNPO protein disruption and disease outcomes, indicating the importance of other factors, including seizure onset and time of therapy initiation. We found that pre-maturity, the delay in initiation of PLP therapy and early onset of seizures correlate with a poor neurocognitive outcome. Given the amenability of PNPO to PLP therapy for seizure control, early diagnosis is essential.

Molecular characterization of pyridoxine 5'-phosphate oxidase and its pathogenic forms associated with neonatal epileptic encephalopathy

Defects of vitamin B₆ metabolism are responsible for severe neurological disorders, such as pyridoxamine 5'-phosphate oxidase deficiency (PNPOD; OMIM: 610090), an autosomal recessive inborn error of metabolism that usually manifests with neonatal-onset severe seizures and subsequent encephalopathy. At present, 27 pathogenic mutations of the gene encoding human PNPO are known, 13 of which are homozygous missense mutations; however, only 3 of them have been characterised with respect to the molecular and functional properties of the variant enzyme forms. Moreover, studies on wild type and variant human PNPOs have so far largely ignored the regulation properties of this enzyme. Here, we present a detailed characterisation of the inhibition mechanism of PNPO by pyridoxal 5'-phosphate (PLP), the reaction product of the enzyme. Our study reveals that human PNPO has an allosteric PLP binding site that plays a crucial role in the enzyme regulation and therefore in the regulation of vitamin B₆ metabolism in humans. Furthermore, we have produced, recombinantly expressed and characterised several PNPO pathogenic variants responsible for PNPOD (G118R, R141C, R225H, R116Q/R225H, and X262Q). Such replacements mainly affect the catalytic activity of PNPO and binding of the enzyme substrate and FMN cofactor, leaving the allosteric properties unaltered.

The multifaceted role of vitamin B6 in cancer: Drosophila as a model system to investigate DNA damage

A perturbed uptake of micronutrients, such as minerals and vitamins, impacts on different human diseases, including cancer and neurological disorders. Several data converge towards a crucial role played by many micronutrients in genome integrity maintenance and in the establishment of a correct DNA methylation pattern. Failure in the proper accomplishment of these processes accelerates senescence and increases the risk of developing cancer, by promoting the formation of chromosome aberrations and deregulating the expression of oncogenes. Here, the main recent evidence regarding the impact of some B vitamins on DNA damage and cancer is summarized, providing an integrated and updated analysis, mainly centred on vitamin B₆. In many cases, it is difficult to finely predict the optimal vitamin rate that is able to protect against DNA damage, as this can be influenced by a given individual's genotype. For this purpose, a precious resort is represented by model organisms which allow limitations imposed by more complex systems to be overcome. In this review, we show that Drosophila can be a useful model to deeply understand mechanisms underlying the relationship between vitamin B₆ and genome integrity.

Variable treatment response in a patient with pyridoxal N phosphate oxidase (PNPO) deficiency- understanding the paradox

A 6-year-old girl presented with history of infantile onset epileptic encephalopathy and developmental delay. She had polymorphic seizures that were refractory to regular anti-seizure medication. Incomplete control of seizures was achieved on starting pyridoxine, riboflavin and thiamine. Clinical exome sequencing done at 4 years revealed PNPO deficiency with a homozygous mutation in the highly conserved exon 3:c.352G > A p.Gly118R region of the gene. Thereafter, pyridoxine was weaned and pyridoxal phosphate was added with resultant refractory status epilepticus, which necessitated our approach to start pyridoxine and stop pyridoxal phosphate. With two antiseizure medication and three vitamins, she had improved seizure control. At 6 years of age an attempt to wean off riboflavin resulted in break through seizures. After restarting riboflavin along with pyridoxal phosphate, pyridoxine in low doses and two antiseizure medications, the child achieved good seizure control. Though partial responsiveness to pyridoxine with gene mutation in the exon 3: c.352G > A p. Gly118R is known, riboflavin dependence and transient worsening of seizures off pyridoxine has not been described to our knowledge. Our case highlights the importance of identifying the precise gene mutationsequence to properly identify variants relative to individual phenotypic expression, treatment responsivness and need for added vitamin supplementation.

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PNPO (pyridoxal N phosphate oxidase) deficiency is a treatable cause of infantile and neonatal onset epileptic encephalopathy

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PNPO deficiency is classically responsive to pyridoxal phosphate but other agents like high dose pyridoxine and riboflavin are also useful depending upon the genetic mutation involved.

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The present report describes a paradoxical worsening which occurred when switched from pyridoxine to pyridoxal phosphate.

Pyridox (am) ine 5'-phosphate oxidase deficiency induces seizures in Drosophila melanogaster

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 neurotransmitters including γ-aminobutyric acid (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 sugarlethal (sgll)-the Drosophila homolog of human PNPO (hPNPO)-and found mutant (sgll95) flies exhibiting a lethal phenotype on a diet devoid of VB6. Here, we report the establishment of both sgll95 and ubiquitous sgll knockdown (KD) flies as valid animal models of PNPO-deficiency-induced epilepsy. Both sgll95 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 the 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.

Diagnostic and Clinical Utility of Clinical Exome Sequencing in Children With Moderate and Severe Global Developmental Delay / Intellectual Disability

Clinical exome sequencing is currently being used in diagnostics of various genetic disorders, but studies supporting its application in clinical setting are scarce. The aim of this study was to establish diagnostic and clinical utility of clinical exome sequencing in patients with moderate and severe global developmental delay/intellectual disability. Clinical diagnosis was made in 49 of 88 investigated patients, with overall diagnostic yield of 55.7%. Molecular findings are characterized in detail, including the impact of newly made diagnosis on clinical management. Several previously unreported genotype-phenotype correlations and 33 novel variants are described. Genetic and clinical data were shared through publicly available database. In conclusion, clinical exome sequencing allows identification of causative variants in a significant proportion of patients in investigated clinical subgroup. Compared to whole exome sequencing, it shows similar diagnostic and clinical utility with reduced costs, which could be of particular importance for institutions with limited resources.

Further Delineation of Pyridoxine-Responsive Pyridoxine Phosphate Oxidase Deficiency Epilepsy: Report of a New Case and Review of the Literature With Genotype-Phenotype Correlation

In recent years, the clinical spectrum of pyridoxine phosphate oxidase (PNPO) deficiency has broadened. There are a growing number of patients with a transient or lasting response to pyridoxine in addition to cases that respond more traditionally to pyridoxal-phosphate. However, among pyridoxine-responsive patients with PNPO gene mutation, there are only a few reports on electroencephalogram (EEG) ictal/interictal patterns, and data regarding the outcomes are inconsistent. We describe a case of neonatal onset epilepsy with missense mutation c(674G>A) p(R225 H) in PNPO gene and pyridoxine responsiveness. Comparing this patient with 24 cases of previously described pyridoxine-responsive pyridoxine phosphate oxidase deficiency epilepsy, we found that patients carrying the missense mutation c(674G>A) p(R225 H) of the PNPO gene might have a more severe epileptic phenotype, possibly because of their lower residual PNPO activity. Indeed, pyridoxine-responsive pyridoxine phosphate oxidase deficiency epilepsy remains a challenge, with neurodevelopmental disabilities occurring in about half of the cases.

Pyridox(am)ine 5'-phosphate oxidase (PNPO) deficiency in zebrafish results in fatal seizures and metabolic aberrations

Pyridox(am)ine 5'-phosphate oxidase (PNPO) catalyzes oxidation of pyridoxine 5'-phosphate (PNP) and pyridoxamine 5'-phosphate (PMP) to pyridoxal 5'-phosphate (PLP), the active form of vitamin B₆. PNPO deficiency results in neonatal/infantile seizures and neurodevelopmental delay. To gain insight into this disorder we generated Pnpo deficient (pnpo^-/-) zebrafish (CRISPR/Cas9 gene editing). Locomotion analysis showed that pnpo^-/- zebrafish develop seizures resulting in only 38% of pnpo^-/- zebrafish surviving beyond 20 days post fertilization (dpf). The age of seizure onset varied and survival after the onset was brief. Biochemical profiling at 20 dpf revealed a reduction of PLP and pyridoxal (PL) and accumulation of PMP and pyridoxamine (PM). Amino acids involved in neurotransmission including glutamate, γ-aminobutyric acid (GABA) and glycine were decreased. Concentrations of several, mostly essential, amino acids were increased in pnpo^-/- zebrafish suggesting impaired activity of PLP-dependent transaminases involved in their degradation. PLP treatment increased survival at 20 dpf and led to complete normalization of PLP, PL, glutamate, GABA and glycine. However, amino acid profiles only partially normalized and accumulation of PMP and PM persisted. Taken together, our data indicate that not only decreased PLP but also accumulation of PMP may play a role in the clinical phenotype of PNPO deficiency.

Assessing the genetic association between vitamin B6 metabolism and genetic generalized epilepsy

Altered vitamin B6 metabolism due to pathogenic variants in the gene PNPO causes early onset epileptic encephalopathy, which can be treated with high doses of vitamin B6. We recently reported that single nucleotide polymorphisms (SNPs) that influence PNPO expression in the brain are associated with genetic generalized epilepsy (GGE). However, it is not known whether any of these GGE-associated SNPs influence vitamin B6 metabolite levels. Such an influence would suggest that vitamin B6 could play a role in GGE therapy. Here, we performed genome-wide association studies (GWAS) to assess the influence of GGE associated genetic variants on measures of vitamin B6 metabolism in blood plasma in 2232 healthy individuals. We also asked if SNPs that influence vitamin B6 were associated with GGE in 3122 affected individuals and 20,244 controls. Our GWAS of vitamin B6 metabolites reproduced a previous association and found a novel genome-wide significant locus. The SNPs in these loci were not associated with GGE. We found that 84 GGE-associated SNPs influence expression levels of PNPO in the brain as well as in blood. However, these SNPs were not associated with vitamin B6 metabolism in plasma. By leveraging polygenic risk scoring (PRS), we found suggestive evidence of higher catabolism and lower levels of the active and transport forms of vitamin B6 in GGE, although these findings require further replication.

Pyridoxamine Supplementation Effectively Reverses the Abnormal Phenotypes of Zebrafish Larvae With PNPO Deficiency

Neonatal epileptic encephalopathy (NEE), as a result of pyridoxine 5′-phosphate oxidase (PNPO) deficiency, is a rare neural disorder characterized by intractable seizures and usually leads to early infant death. The clinical phenotypes do not respond to antiepileptic drugs but are alleviated in most cases by giving large doses of pyridoxal 5′-phosphate (PLP). PLP is the active form of vitamin B6 participating in more than 100 enzymatic pathways. One of the causes of NEE is pathogenic mutations in the gene for human PNPO (hPNPO). PNPO is a key enzyme in converting pyridoxine (PN), the common dietary form of vitamin B6, and some other B6 vitamers to PLP. More than 25 different mutations in hPNPO, which result in reduced catalytic activity, have been described for PNPO-deficiency NEE. To date, no animal model is available to test new therapeutic strategies. In this report, we describe using zebrafish with reduced activity of Pnpo as an animal model. Knocking down zPnpo resulted in developmental anomalies including brain malformation and impaired locomotor activity, similar to the clinical features of PNPO-deficiency NEE. Other anomalies include a defective circulation system. These anomalies were significantly alleviated by co-injecting either zpnpo or hPNPO mRNAs. As expected from clinical observations in humans, supplementing with PLP improved the morphological and behavioral anomalies. PN only showed marginal positive effects, and only in a few anomalies. Remarkably, pyridoxamine (PM), another dietary form of vitamin B6, showed rescue effects even at a lower concentration than PLP, presenting a possible new therapeutic treatment for PNPO-deficiency NEE. Finally, GABA, a neurotransmitter whose biosynthesis depends on a PLP-dependent enzyme, showed some positive rescue effect. These results suggest zebrafish to be a promising PNPO-deficiency model for studying PLP homeostasis and drug therapy in vivo.

Update on the treatment of vitamin B6 dependent epilepsies

Introduction: Vitamin B6 dependent epilepsies are a group of treatable diseases (ALDH7A1 deficiency, PNPO deficiency, PLP binding protein deficiency, hyperprolinaemia type II and hypophosphatasia and glycosylphosphatidylinositol anchor synthesis defects) responding to pyridoxine or pyridoxal-5^I-phosphate. Areas covered: A critical review was conducted on the therapeutic management of all the reported patients with genetically confirmed diagnoses of diseases affecting vitamin B6 metabolism and presenting with pyridoxine or pyridoxal-5^I-phosphate dependent-seizures. Data about safety and efficacy were analyzed as well as the management of supplementation with pyridoxine or pyridoxal-5^I-phosphate both in the acute phases and in the maintenance therapies. The authors also analyzed alternative therapeutic strategies for ALDH7A1 deficiency (lysine-restricted diet, arginine supplementation, oligonucleotide antisense therapy, upstream inhibition of aminoadipic semialdehyde synthase). Expert opinion: The administration of pyridoxine or pyridoxal-5^I-phosphate should be considered in all intractable seizures also beyond the first year of life. Lysine restricted diet and arginine supplementation should be introduced in all the confirmed ALDH7A1 deficient patients. Pre or post-natal supplementation with pyridoxine should be given in familial cases until an eventual molecular genetic disconfirmation. Minor data about alternative therapies are available for other disorders of vitamin B6 metabolism.

Disorders affecting vitamin B6 metabolism

Vitamin B₆ is present in our diet in many forms, however, only pyridoxal 5'-phosphate (PLP) can function as a cofactor for enzymes. The intestine absorbs nonphosphorylated B₆ vitamers, which are converted by specific enzymes to the active PLP form. The role of PLP is enabled by its reactive aldehyde group. Pathways reliant on PLP include amino acid and neurotransmitter metabolism, folate and 1-carbon metabolism, protein and polyamine synthesis, carbohydrate and lipid metabolism, mitochondrial function and erythropoiesis. Besides the role of PLP as a cofactor B₆ vitamers also play other cellular roles, for example, as antioxidants, modifying expression and action of steroid hormone receptors, affecting immune function, as chaperones and as an antagonist of Adenosine-5'-triphosphate (ATP) at P2 purinoceptors. Because of the vital role of PLP in neurotransmitter metabolism, particularly synthesis of the inhibitory transmitter γ-aminobutyric acid, it is not surprising that various inborn errors leading to PLP deficiency manifest as B₆ -responsive epilepsy, usually of early onset. This includes pyridox(am)ine phosphate oxidase deficiency (a disorder affecting PLP synthesis and recycling), disorders affecting PLP import into the brain (hypophosphatasia and glycosylphosphatidylinositol anchor synthesis defects), a disorder of an intracellular PLP-binding protein (PLPBP, previously named PROSC) and disorders where metabolites accumulate that inactivate PLP, for example, ALDH7A1 deficiency and hyperprolinaemia type II. Patients with these disorders can show rapid control of seizures in response to either pyridoxine and/or PLP with a lifelong dependency on supraphysiological vitamin B₆ supply. The clinical and biochemical features of disorders leading to B₆ -responsive seizures and the treatment of these disorders are described in this review.

Genome-wide mega-analysis identifies 16 loci and highlights diverse biological mechanisms in the common epilepsies

The epilepsies affect around 65 million people worldwide and have a substantial missing heritability component. We report a genome-wide mega-analysis involving 15,212 individuals with epilepsy and 29,677 controls, which reveals 16 genome-wide significant loci, of which 11 are novel. Using various prioritization criteria, we pinpoint the 21 most likely epilepsy genes at these loci, with the majority in genetic generalized epilepsies. These genes have diverse biological functions, including coding for ion-channel subunits, transcription factors and a vitamin-B6 metabolism enzyme. Converging evidence shows that the common variants associated with epilepsy play a role in epigenetic regulation of gene expression in the brain. The results show an enrichment for monogenic epilepsy genes as well as known targets of antiepileptic drugs. Using SNP-based heritability analyses we disentangle both the unique and overlapping genetic basis to seven different epilepsy subtypes. Together, these findings provide leads for epilepsy therapies based on underlying pathophysiology.

Epilepsies are common brain disorders and are classified based on clinical phenotyping, imaging and genetics. Here, the authors perform genome-wide association studies for 3 broad and 7 subtypes of epilepsy and identify 16 loci - 11 novel - that are further annotated by eQTL and partitioned heritability analyses.

Testing for Inborn Errors of Metabolism

PURPOSE OF REVIEW

This article provides an overview of genetic metabolic disorders that can be identified by metabolic tests readily available to neurologists, such as tests for ammonia, plasma amino acids, and urine organic acids. The limitations of these tests are also discussed, as they only screen for a subset of the many inborn errors of metabolism that exist.

RECENT FINDINGS

Advances in next-generation sequencing and the emerging use of advanced metabolomic screening have made it possible to diagnose treatable inborn errors of metabolism that are not included in current newborn screening programs. Some of these inborn errors of metabolism are especially likely to present with nonspecific neurologic phenotypes, such as epilepsy, ataxia, or intellectual disability. However, cost may be a barrier to obtaining these newer tests. It is important to keep in mind that common metabolic testing may lead to treatable diagnoses. Resources are available to guide neurologists in diagnosing genetic metabolic conditions.

SUMMARY

This article introduces the clinical presentations of treatable inborn errors of metabolism that are important for neurologists to consider in patients of all ages. Inborn errors of metabolism are rare, but they can present with neurologic symptoms. Newborns are now screened for many treatable metabolic disorders, but these screening tests may miss milder presentations of treatable inborn errors of metabolism that present later in life. These patients may present to adult neurologists who may be less likely to consider metabolic genetic testing.

Nutrients and Neurology

PURPOSE OF REVIEW

This article provides an update on the clinical presentation and management of neurologic disease related to key nutrient deficiencies.

RECENT FINDINGS

Major advances have been made in understanding the pathway related to vitamin B12 absorption and distribution. It is now known that deficiencies of vitamin B12 and copper have similar neurologic manifestations. Bariatric surgery is a risk factor for both. Alcoholism is just one of the many causes of thiamine deficiency. Early neurologic complications following bariatric surgery are often due to thiamine deficiency. Encephalopathy in the setting of alcoholism that persists despite thiamine replacement should prompt consideration of niacin deficiency. Pyridoxine deficiency and toxicity both have neurologic sequelae. Vitamin D deficiency and the risk for multiple sclerosis has been an area of ongoing research.

SUMMARY

Optimal functioning of the nervous system is dependent on a constant supply of certain vitamins and nutrients. This article discusses neurologic manifestations related to deficiency of these key nutrients.

Inborn Errors of Metabolism with Seizures: Defects of Glycine and Serine Metabolism and Cofactor-Related Disorders

Inborn errors of metabolism (IEM) are relatively uncommon causes for seizures in children; however, they should be considered in the differential diagnosis because several IEM are potentially treatable and seizures can be resolved if appropriate treatment is initiated. Clues from clinical presentation, physical examination, laboratory tests, and brain imaging can raise the possibility of IEM. Several IEM can present with seizures, either as the main presenting finding or as a part of a more complex phenotype. These include cofactor-related disorders, glycine and serine metabolism defects, and other disorders.

Pyridoxine-dependent epilepsies: an observational study on clinical, diagnostic, therapeutic and prognostic features in a pediatric cohort

The aim of our study was to describe the clinical, electroencephalogram, molecular findings and the diagnostic and therapeutic flow-chart of children with pyridoxine-dependent epilepsies (PDEs). We performed a retrospective observational study on children with PDEs, diagnosed and followed-up in Italian Pediatric Departments. In each centre, the authors collected data from a cohort of children admitted for intractable seizures, responsive to pyridoxine administration and resistant to other anticonvulsant therapies. Data were retrospectively analysed from January 2016 to January 2017. Sixteen patients (13 males, and 3 females) were included. We found that 93.75% of patients underwent conventional anticonvulsant therapy before starting pyridoxine administration and 62.5% had ex-juvantibus diagnosis, as specific serum diagnostic tests had been performed in only 37.5% of patients by alpha-AASA and pipecolic acid blood and urine dosage. The most common type of seizure was generalized tonic-clonic in 7 patients and the most common EEG pattern was characterized by a "burst suppression" pattern. Before pyridoxine administration, other anticonvulsant drugs were used in 93.75% of patients, with consequent onset of drug-resistance. Phenobarbital was the most frequently used drug as first-line treatment. The importance of our study relies on the need of a deeper knowledge of PDEs in terms of early diagnosis, avoiding incorrect treatment and related adverse events, clinical and EEG pathognomonic features, and genetic aspects of the disease.

Systemic Manifestations in Pyridox(am)ine 5'-Phosphate Oxidase Deficiency

OBJECTIVE

Pyridoxine is converted to its biologically active form pyridoxal-5-phosphate (P5P) by the enzyme pyridox(am)ine 5'-phosphate oxidase and serves as a cofactor in nearly 200 reactions in the central nervous system. Pyridox(am)ine 5'-phosphate oxidase deficiency leads to P5P dependent epilepsy, typically a neonatal- or infantile-onset epileptic encephalopathy treatable with P5P or in some cases, pyridoxine. Following identification of retinopathy in a patient with pyridox(am)ine 5'-phosphate oxidase deficiency that was reversible with P5P therapy, we describe the systemic manifestations of pyridox(am)ine 5'-phosphate oxidase deficiency.

METHODS

A series of six patients with homozygous mutations of PNPO, the gene coding pyridox(am)ine 5'-phosphate oxidase, were evaluated in our center over the course of two years for phenotyping of neurological and systemic manifestations.

RESULTS

Five of six were born prematurely, three had anemia and failure to thrive, and two had elevated alkaline phosphatase. A movement disorder was observed in two children, and a reversible retinopathy was observed in the most severely affected infant. All patients had neonatal-onset epilepsy and were on a continuum of developmental delay to profound encephalopathy. Electroencephalographic features included background slowing and disorganization, absent sleep features, and multifocal and generalized epileptiform discharges. All the affected probands carried a homozygous PNPO mutation (c.674 G>T, c.686 G>A and c.352G>A).

CONCLUSION

In addition to the well-described epileptic encephalopathy, pyridox(am)ine 5'-phosphate oxidase deficiency causes a range of neurological and systemic manifestations. A movement disorder, developmental delay, and encephalopathy, as well as retinopathy, anemia, and failure to thrive add to the broadening clinical spectrum of P5P dependent epilepsy.

Pyridoxine-5'-phosphate oxidase (Pnpo) deficiency: Clinical and biochemical alterations associated with the C.347g>A (P.·Arg116gln) mutation

BACKGROUND

Pyridoxal-5^'-phosphate oxidase (PNPO) deficiency presents as a severe neonatal encephalopathy responsive to pyridoxal-5^'-phosphate (PLP) or pyridoxine. Recent studies widened the phenotype of this condition and detected genetic variants on PNPO gene whose pathogenic role and clinical expression remain to be established.

OBJECTIVE

This paper aims to characterize the functional effects of the c.347G>A (p.Arg116Gln) mutation in the PNPO gene in order to define its pathogenicity and describe the clinical features of new patients with epilepsy carrying this mutation.

METHODS

Arg116Gln protein variant was expressed as recombinant protein. The mutant protein was characterized with respect to structural and kinetic properties, thermal stability, binding constants of cofactor (FMN) and product (PLP). We also reviewed clinical data of 3 new patients carrying the mutation.

RESULTS

The Arg116Gln mutation does not alter the overall enzyme structure and only slightly affects its catalytic efficiency; nevertheless, this mutation affects thermal stability of PNPO, reduces its affinity for FMN and impairs transfer of PLP to PLP-dependent enzymes. Three boys with seizure onset between 8months and 3years of age, carrying the Arg116Gln mutation, are described. These three patients exhibited different seizure types associated with interictal EEG abnormalities and slow background activity. Mild/moderate intellectual disability was observed in 2/3 patients. A dramatic therapeutic response to pyridoxine was observed in the only patient who still had active seizures when starting treatment, while in all three patients interictal EEG discharges and background activity improved after pyridoxine treatment was initiated.

CONCLUSIONS

The reported data support a pathogenic role of the c.347G>A (p.Arg116Gln) mutation in PNPO deficiency. The later onset of symptoms and the milder epilepsy phenotype of these expand the disease phenotype.

An LC-MS/MS-Based Method for the Quantification of Pyridox(am)ine 5'-Phosphate Oxidase Activity in Dried Blood Spots from Patients with Epilepsy

We report the development of a rapid, simple, and robust LC-MS/MS-based enzyme assay using dried blood spots (DBS) for the diagnosis of pyridox(am)ine 5'-phosphate oxidase (PNPO) deficiency (OMIM 610090). PNPO deficiency leads to potentially fatal early infantile epileptic encephalopathy, severe developmental delay, and other features of neurological dysfunction. However, upon prompt treatment with high doses of vitamin B₆, affected patients can have a normal developmental outcome. Prognosis of these patients is therefore reliant upon a rapid diagnosis. PNPO activity was quantified by measuring pyridoxal 5'-phosphate (PLP) concentrations in a DBS before and after a 30 min incubation with pyridoxine 5'-phosphate (PNP). Samples from 18 PNPO deficient patients (1 day-25 years), 13 children with other seizure disorders receiving B₆ supplementation (1 month-16 years), and 37 child hospital controls (5 days-15 years) were analyzed. DBS from the PNPO-deficient samples showed enzyme activity levels lower than all samples from these two other groups as well as seven adult controls; no false positives or negatives were identified. The method was fully validated and is suitable for translation into the clinical diagnostic arena.

Pyridoxine dependent epilepsies: new therapeutical point of view

Pyridoxine dependent epilepsies (PDEs) are rare autosomal recessive disorders with onset in neonatal period. Seizures are typically not responsive to conventional antiepileptic drugs, but they cease after parental pyridoxine administration. Atypical forms are characterized partly response to pyridoxine and a late onset of symptoms (up to the age of three years). Prevalence is variable and it has rarely been described. The genes involved in PDEs are the gene encoding for the Alpha-aminoadipic-semialdehyde dehydrogenase (ALDH7A1) and PROSC gene, which encodes a pyridoxal-5-phosphate binding protein. Mutations in the gene encoding for the pyridoxal-5′-phosphate oxidase enzyme (PNPO) are responsible of a clinical entity similar to PDEs responsive to pyridoxal-5-phosphate administration not to pyridoxine administration. PDEs diagnosis is often delayed because they are suspected only after conventional anticonvulsant drugs resistance.

Herein authors aim to present an expert point of view on PDEs in childhood, reviewing the most recent literature data and proposing a new therapeutical approach for seizures of unknown origin in all those children up to the age of three years.

Novel phenotypes of pyridox(am)ine-5'-phosphate oxidase deficiency and high prevalence of c.445_448del mutation in Chinese patients

To analyze the clinical and genetic characteristics of Chinese patients with pyridox(am)ine-5'-phosphate oxidase (PNPO) deficiency. The clinical presentations and the responses to treatments were analyzed in 4 patients. Blood and urinary metabolic screenings, electroencephalogram (EEG), brain magnetic resonance imaging (MRI) and epilepsy-related genes detection were performed in all patients. Patient 1 and 2 were identical twin brothers, who were born at 35⁺⁵ w gestation with a sign of encephalopathy. Their seizures started within the first day and could not be controlled by pyridoxine or pyridoxal-5'-phosphate (PLP) completely. Patient 3 presented seizures at 5 months, responding well to pyridoxine. Seizures in patient 4 began at 40 days after birth and were controlled by valproic acid and topiramate. EEG showed atypical hypsarrhythmia or multifocal epileptiform discharges in 3 patients, and showed normality in patient 4. MRI showed nonspecific abnormality or normality. Blood metabolic screening showed multiple amino acids level abnormalities in all cases. Urinary metabolic screening showed vanillactic acid prominently elevated in 3 patients. Genetic analysis revealed 5 mutations of PNPO, three of which were novel. The mutation c.445_448del was carried by the twins and patient 3. Assessment of psychomotor development indicated severe delay in 3 patients and borderline to mild delay in patient 3. This is the first time to report patients with PNPO deficiency diagnosed by gene analysis in China. The novel clinical characteristics and novel mutations found here expanded the phenotypes and genotypes of this disease. Further, the frameshift mutation c.445_448del might be high prevalence in PNPO deficiency in Chinese patients.

Treatable Genetic Metabolic Epilepsies

OPINION STATEMENT

In the absence of a culprit epileptogenic lesion, pharmacoresistant seizures should prompt the physician to consider potentially treatable metabolic epilepsies, especially in the presence of developmental delays. Even though the anti-seizure treatment of the epilepsies remains symptomatic and usually tailored to an electroclinical phenotype rather than to an underlying etiology, a thorough metabolic workup might reveal a disease with an etiology-specific treatment. Early diagnosis is essential in the case of treatable metabolic epilepsies allowing timely intervention. Despite the advances in genetic testing, biochemical testing including cerebrospinal fluid studies are still needed to expedite the diagnostic workup and potential therapeutic trials. The diagnostician should have a high index of suspicion despite potential clinical digressions from seminal publications describing the initial cases, as these index patients may represent the most severe form of the condition rather than its most common presenting form. The often gratifying developmental outcome and seizure control with early treatment calls for a prompt diagnostic consideration of treatable metabolic diseases; even though relatively rare or potentially only seemingly so.

Inborn Errors of Metabolism and Epilepsy: Current Understanding, Diagnosis, and Treatment Approaches

Inborn errors of metabolism (IEM) are a rare cause of epilepsy, but seizures and epilepsy are frequently encountered in patients with IEM. Since these disorders are related to inherited enzyme deficiencies with resulting effects on metabolic/biochemical pathways, the term “metabolic epilepsy” can be used to include these conditions. These epilepsies can present across the life span, and share features of refractoriness to anti-epileptic drugs, and are often associated with co-morbid developmental delay/regression, intellectual, and behavioral impairments. Some of these disorders are amenable to specific treatment interventions; hence timely and appropriate diagnosis is critical to improve outcomes. In this review, we discuss those disorders in which epilepsy is a dominant feature and present an approach to the clinical recognition, diagnosis, and management of these disorders, with a greater focus on primarily treatable conditions. Finally, we propose a tiered approach that will permit a clinician to systematically investigate, identify, and treat these rare disorders.

Quality and stability of extemporaneous pyridoxal phosphate preparations used in the treatment of paediatric epilepsy

Objectives

To assess the pyridoxal 5′-phosphate (PLP) content and stability of extemporaneous PLP liquids prepared from dietary supplements used for the treatment of vitamin B6-dependent epilepsy.

Methods

Pyridoxal 5′-phosphate liquids were prepared in accordance with the guidelines given to patients from marketed 50 mg PLP dietary capsules and tablets. The PLP content and its stability were evaluated under conditions resembling the clinical setting using reverse phase HPLC and mass spectrometry.

Key findings

Pyridoxal 5′-phosphate content in most of the extemporaneously prepared liquids from dietary supplements was found to be different from the expected amount (~16–60 mg). Most of these PLP extemporaneous liquids were stable at room temperature (protected from light) after 24 h but unstable after 4 h when exposed to light. A key photodegradation product of PLP in water was confirmed as 4-pyridoxic acid 5′-phosphate (PAP).

Conclusion

Pyridoxal 5′-phosphate tablets from Solgar® were found to be the most reliable product for the preparation of extemporaneous PLP liquids. This work highlighted the difference between the marketed PLP dietary supplements quality and the importance of proper storage of aqueous PLP. There is a need to develop pharmaceutical forms of PLP that ensure dose accuracy and avoid potentially unsafe impurities with the aim of enhancing safety and compliance.

Current knowledge for pyridoxine-dependent epilepsy: a 2016 update

Pyridoxine-dependent epilepsy (PDE) is a rare genetic condition characterized by intractable and recurrent neonatal seizures that are uniquely alleviated by high doses of pyridoxine (vitamin B6). This recessive disease is caused by mutations in ALDH7A1, a gene encoding Antiquitin, an enzyme central to lysine degradation. This results in the pathogenic accumulation of the lysine intermediates Aminoadipate Semialdehyde (AASA) and its cyclic equilibrium form Piperideine-6-carboxylate (P6C) in body fluids; P6C reacts with pyridoxal-5'-phosphate (PLP, the active form of vitamin B6) causing its inactivation and leading to pyridoxine-dependent seizures. While PDE is responsive to pharmacological dosages of pyridoxine, despite lifelong supplementation, neurodevelopment delays are observed in >75% of PDE cases. Thus, adjunct treatment strategies are emerging to both improve seizure control and moderate the delays in cognition. These adjunctive therapies, lysine restriction and arginine supplementation, separately or in combination (with pyridoxine thus termed 'triple therapy'), have shown promising results and are recommended in all PDE patients. Other new therapeutic strategies currently in preclinical phase of study include antisense therapy and substrate reduction therapy. We present here a comprehensive review of current treatment options as well as PDE phenotype, differential diagnosis, current management and views upon the future of PDE research.

Pyridoxal Phosphate Supplementation in Neuropediatric Disorders

Pyridoxal phosphate (PLP) is the active form of vitamin B₆ and a cofactor in many enzyme reactions including neurotransmitter metabolism. PLP metabolism disturbances may mostly lead to refractory seizures. In this report, we review the main pathophysiological factors related with PLP deficiency and our experience in PLP treatment in pediatric patients with low-normal cerebrospinal fluid PLP values who presented epilepsy. Only one case had a definite diagnosis (Phelan-McDermid syndrome). The results of extensive metabolic workups and targeted genetic studies were normal for all patients. In 5 cases, the response to PLP supplementation (10-30mg/kg/d) was initially positive. PLP adverse reactions were noticed in 4 patients and PLP was discontinued; however, one of the most noticeable symptoms was an asymptomatic increase in liver enzymes. These negative results with PLP supplementation are worth reporting, to improve the information we use to treat our patients.

Epilepsy in Inborn Errors of Metabolism With Therapeutic Options

Inborn errors of metabolism (IEM) are rare conditions that represent more than 1000 diseases, with a global prevalence of approximately 1:2000 individuals. Approximately, 40%-60% of IEM may present with epilepsy as one of the main neurologic signs. Epilepsy in IEM may appear at any age (fetal, newborn, infant, adolescent, or even adult). Different pathophysiological mechanisms may be responsible for the clinical phenotype, such as disturbances in energy metabolism (mitochondrial and fatty oxidation disorders, GLUT-1, and cerebral creatine deficiency), accumulation of complex molecules (lysosomal storage disorders), toxic mechanisms (organic acidurias and urea cycle disorders), or impairment of neurotransmission. Early diagnosis and, in some cases, an effective treatment may result in an excellent evolution of the IEM, in particularly seizure control. This review attempts to delineate a summary of IEM that may present with seizures or epilepsy and emphasizes the management in treatable conditions.

The value of plasma vitamin B6 profiles in early onset epileptic encephalopathies

BACKGROUND

Recent decades have unravelled the molecular background of a number of inborn errors of metabolism (IEM) causing vitamin B6-dependent epilepsy. As these defects interfere with vitamin B6 metabolism by different mechanisms, the plasma vitamin B6 profile can give important clues for further molecular work-up. This has so far been investigated in only a small number of patients.

METHODS

We evaluated the vitamin B6 vitamers pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN) and the catabolite pyridoxic acid (PA) in the so far largest patient cohort: reference (n = 50); pyridox(am)ine 5'-phosphate oxidase (PNPO) deficiency (n = 6); antiquitin (ATQ) deficiency (n = 21); tissue non-specific alkaline phosphatase (TNSALP) deficiency (n = 2) and epileptic encephalopathy (EE) of unknown etiology tested negative for ATQ and PNPO deficiency (n = 64).

RESULTS

High plasma PM concentration was found in all patients with PNPO deficiency irrespective of vitamin B6 supplementation. Their PM concentration and the PM/PA ratio was significantly higher (p < 0.0001), compared to any other patients analysed. One patient with TNSALP deficiency and sampling prior to PN supplementation had markedly elevated plasma PLP concentration. On PN supplementation, patients with TNSALP deficiency, ATQ deficiency and patients of the EE cohort had similar plasma vitamin B6 profiles that merely reflect the intake of supra-physiological doses of vitamin B6. The interval of sampling to the last PN intake strongly affected the plasma concentrations of PN, PL and PA.

CONCLUSIONS

PM concentrations and the PM/PA ratio clearly separated PNPO-deficient patients from the other cohorts. The plasma PM/PA ratio thus represents a robust biomarker for the selective screening of PNPO deficiency.

Pyridoxine-Dependent Epilepsy: An Expanding Clinical Spectrum

BACKGROUND

Pyridoxine-dependent epilepsy is a rare autosomal recessive epileptic encephalopathy caused by antiquitin (ALDH7A1) deficiency. In spite of adequate seizure control, 75% of patients suffer intellectual developmental disability. Antiquitin deficiency affects lysine catabolism resulting in accumulation of α-aminoadipic semialdehyde/pyrroline 6' carboxylate and pipecolic acid. Beside neonatal refractory epileptic encephalopathy, numerous neurological manifestations and metabolic/biochemical findings have been reported.

METHODS AND RESULTS

We present a phenotypic spectrum of antiquitin deficiency based on a literature review (2006 to 2015) of reports (n = 49) describing the clinical presentation of confirmed patients (n > 200) and a further six patient vignettes. Possible presentations include perinatal asphyxia; neonatal withdrawal syndrome; sepsis; enterocolitis; hypoglycemia; neuroimaging abnormalities (corpus callosum and cerebellar abnormalities, hemorrhage, white matter lesions); biochemical abnormalities (lactic acidosis, electrolyte disturbances, neurotransmitter abnormalities); and seizure response to pyridoxine, pyridoxal-phosphate, and folinic acid dietary interventions.

DISCUSSION

The phenotypic spectrum of pyridoxine-dependent epilepsy is wide, including a myriad of neurological and systemic symptoms. Its hallmark feature is refractory seizures during the first year of life. Given its amenability to treatment with lysine-lowering strategies in addition to pyridoxine supplementation for optimal seizure control and developmental outcomes, early diagnosis of pyridoxine-dependent epilepsy is essential. All infants presenting with unexplained seizures should be screened for antiquitin deficiency by determination of α-aminoadipic semialdehyde/pyrroline 6' carboxylate (in urine, plasma or cerebrospinal fluid) and ALDH7A1 molecular analysis.

Amenable Treatable Severe Pediatric Epilepsies

Vitamin-dependent epilepsies and multiple metabolic epilepsies are amenable to treatment that markedly improves the disease course. Knowledge of these amenably treatable severe pediatric epilepsies allows for early identification, testing, and treatment. These disorders present with various phenotypes, including early onset epileptic encephalopathy (refractory neonatal seizures, early myoclonic encephalopathy, and early infantile epileptic encephalopathy), infantile spasms, or mixed generalized seizure types in infancy, childhood, or even adolescence and adulthood. The disorders are presented as vitamin responsive epilepsies such as pyridoxine, pyridoxal-5-phosphate, folinic acid, and biotin; transportopathies like GLUT-1, cerebral folate deficiency, and biotin thiamine responsive disorder; amino and organic acidopathies including serine synthesis defects, creatine synthesis disorders, molybdenum cofactor deficiency, and cobalamin deficiencies; mitochondrial disorders; urea cycle disorders; neurotransmitter defects; and disorders of glucose homeostasis. In each case, targeted intervention directed toward the underlying metabolic pathophysiology affords for the opportunity to significantly effect the outcome and prognosis of an otherwise severe pediatric epilepsy.

Pyridoxine responsive epilepsy caused by a novel homozygous PNPO mutation

We report a patient with anti-epileptic treatment refractory neonatal seizures responsive to pyridoxine. Biochemical analysis revealed normal markers for antiquitin deficiency and also mutation analysis of the ALDH7A1 (Antiquitin) gene was negative. Mutation analysis of the PNPO gene revealed a novel, homozygous, presumed pathogenic mutation (c.481C > T; p.(Arg161Cys)). Measurements of B6 vitamers in a CSF sample after pyridoxine administration revealed elevated pyridoxamine as the only metabolic marker for PNPO deficiency. With pyridoxine monotherapy the patient is seizure free and neurodevelopmental outcome at the age of 14 months is normal.

Neonatal seizures-part 2: Aetiology of acute symptomatic seizures, treatments and the neonatal epilepsy syndromes

Most neonatal epileptic seizures are provoked by an underlying condition or problem-'acute symptomatic seizures'. However, a few neonatal epilepsy syndromes exist, and these are defined by the constellation of seizure types, EEG findings and family history seen. Making an accurate diagnosis of an epilepsy syndrome can help direct investigations, treatment options and provide prognostic information. This article discusses the investigative approach and treatments for neonatal epileptic seizures, including the neonatal epilepsy syndromes.