Pyridoxine responsive epilepsy caused by a novel homozygous PNPO mutation

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.

B vitamin supply in plants and humans: the importance of vitamer homeostasis

B vitamins are a group of water-soluble micronutrients that are required in all life forms. With the lack of biosynthetic pathways, humans depend on dietary uptake of these compounds, either directly or indirectly, from plant sources. B vitamins are frequently given little consideration beyond their role as enzyme accessory factors and are assumed not to limit metabolism. However, it should be recognized that each individual B vitamin is a family of compounds (vitamers), the regulation of which has dedicated pathways. Moreover, it is becoming increasingly evident that individual family members have physiological relevance and should not be sidelined. Here, we elaborate on the known forms of vitamins B₁ , B₆ and B₉ , their distinct functions and importance to metabolism, in both human and plant health, and highlight the relevance of vitamer homeostasis. Research on B vitamin metabolism over the past several years indicates that not only the total level of vitamins but also the oft-neglected homeostasis of the various vitamers of each B vitamin is essential to human and plant health. We briefly discuss the potential of plant biology studies in supporting human health regarding these B vitamins as essential micronutrients. Based on the findings of the past few years we conclude that research should focus on the significance of vitamer homeostasis - at the organ, tissue and subcellular levels - which could improve the health of not only humans but also plants, benefiting from cross-disciplinary approaches and novel technologies.

A vitamin a day keeps the doctor away: The need for high quality pyridoxal-5'-phosphate

BACKGROUND

A rare subset of vitamin B6 responsive seizure disorders does not respond to pyridoxine, and requires the active form of vitamin B6, pyridoxal-5'-phosphate (PLP), to maintain seizure control. Patients with PLP-responsive seizures are dependent on chronic PLP treatment, yet no licensed PLP product is available. PLP food supplements, a product category regulated less stringently than medication, may prove of insufficient effectiveness and safety. Here we describe and discuss three patient scenarios which illustrate this conundrum.

METHODS

Medical and laboratory records were reviewed with retrospective extraction for three unrelated patients who suffered complications during treatment with PLP food supplements.

RESULTS

- Two cases of PNPO deficiency and one case of PLP-dependent epileptic encephalopathy without a (genetic) diagnosis are reported. These patients are critically dependent on PLP for seizure control and have suffered complications due to insufficient quality of these food supplements during the course of treatment. Complications include the occurrence of seizures following the administration of suspected low quality PLP, inactive PLP due to light exposure, a PLP intoxication, resisting administration and post-administration vomiting as a result of the ingestion of large amounts of capsules per day.

CONCLUSION

- This case series illustrates that the reliance on food supplements as anti-seizure therapy is not without risk. The treatment of PLP-dependent seizures exemplifies that PLP is administered as medication, thus there is a clear need for licensed vitamin products of pharmaceutical quality.

New and emerging pharmacologic treatments for developmental and epileptic encephalopathies

PURPOSE OF REVIEW

Summarize evidence on Developmental and Epileptic Encephalopathies (DEEs) treatments focusing on new and emerging pharmacologic therapies (see Video, http://links.lww.com/CONR/A61, Supplementary Digital Content 1, which provides an overview of the review).

RECENT FINDINGS

Advances in the fields of molecular genetics and neurobiology have led to the recognition of underlying pathophysiologic mechanisms involved in an increasing number of DEEs that could be targeted with precision therapies or repurposed drugs, some of which are currently being evaluated in clinical trials. Prompt, optimal therapy is critical, and promising therapies approved or in clinical trials for tuberous sclerosis complex, Dravet and Lennox-Gastaut Syndromes including mammalian target of rapamycin inhibitors, selective membrane channel and antisense oligonucleotide modulation, and repurposed drugs such as fenfluramine, stiripentol and cannabidiol, among others, may improve seizure burden and neurological outcomes. There is an urgent need for collaborative efforts to evaluate the efficacy and safety of emerging DEEs therapies.

SUMMARY

Development of new therapies promise to address unmet needs for patients with DEEs, including improvement of neurocognitive function and quality of life.

Characterization of Novel Pathogenic Variants Causing Pyridox(am)ine 5'-Phosphate Oxidase-Dependent Epilepsy

Several variants of the enzyme pyridox(am)ine 5′-phosphate oxidase (PNPO), responsible for a rare form of vitamin B₆-dependent neonatal epileptic encephalopathy known as PNPO deficiency (PNPOD), have been reported. However, only a few of them have been characterised with respect to their structural and functional properties, despite the fact that the knowledge of how variants affect the enzyme may clarify the disease mechanism and improve treatment. Here, we report the characterisation of the catalytic, allosteric and structural properties of recombinantly expressed D33V, R161C, P213S, and E50K variants, among which D33V (present in approximately 10% of affected patients) is one of the more common variants responsible for PNPOD. The D33V and E50K variants have only mildly altered catalytic properties. In particular, the E50K variant, given that it has been found on the same chromosome with other known pathogenic variants, may be considered non-pathogenic. The P213S variant has lower thermal stability and reduced capability to bind the FMN cofactor. The variant involving Arg161 (R161C) largely decreases the affinity for the pyridoxine 5′-phosphate substrate and completely abolishes the allosteric feedback inhibition exerted by the pyridoxal 5′-phosphate product.

Increased hippocampal excitability in miR-324-null mice

MicroRNAs are non-coding RNAs that act to downregulate the expression of target genes by translational repression and degradation of messenger RNA molecules. Individual microRNAs have the ability to specifically target a wide array of gene transcripts, therefore allowing each microRNA to play key roles in multiple biological pathways. miR-324 is a microRNA predicted to target thousands of RNA transcripts and is expressed far more highly in the brain than in any other tissue, suggesting that it may play a role in one or multiple neurological pathways. Here we present data from the first global miR-324-null mice, in which increased excitability and interictal discharges were identified in vitro in the hippocampus. RNA sequencing was used to identify differentially expressed genes in miR-324-null mice which may contribute to this increased hippocampal excitability, and 3'UTR luciferase assays and western blotting revealed that two of these, Suox and Cd300lf, are novel direct targets of miR-324. Characterisation of microRNAs that produce an effect on neurological activity, such as miR-324, and identification of the pathways they regulate will allow a better understanding of the processes involved in normal neurological function and in turn may present novel pharmaceutical targets in treating neurological disease.

Complexities of pyridoxine response in PNPO deficiency

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Treatment of PNPO deficiency related neonatal status epilepticus is challenging.

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Pyridoxine responsiveness is seen in huge number of cases of PNPO deficiency.

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Various phenotypic variants in terms of response to pyridoxine are known in PNPO disorder making the treatment complex.

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Immediate complete cessation of seizures or normalization of EEG on pyridoxine or pyridoxal 5 phosphate therapy is not necessary for the diagnosis, and treatment should be continued till the genetic tests are available.

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.

Altered hippocampal kynurenine pathway metabolism contributes to hyperexcitability in human mesial temporal lobe epilepsy-hippocampal sclerosis

BACKGROUND AND PURPOSE

Glutamate receptor-mediated enhanced excitatory neurotransmission is typically associated with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). Kynurenic acid and quinolinic acid are two important tryptophan-kynurenine pathway metabolites that modulate glutamate receptor activity. This study was designed to test the hypothesis that alteration in metabolism of tryptophan-kynurenine pathway metabolites in the hippocampus of patients with MTLE-HS contributes to abnormal glutamatergic transmission.

EXPERIMENTAL APPROACH

Levels of tryptophan-kynurenine pathway metabolites were determined using HPLC and LC-MS/MS in hippocampal samples from patients with MTLE-HS, compared with autopsy and non-seizure control samples. mRNA and protein expressions of tryptophan-kynurenine pathway enzymes were determined by qPCR and Western blot. Spontaneous glutamatergic activities were recorded from pyramidal neurons in the presence of kynurenine and kynurenic acid, using whole-cell patch clamp.

KEY RESULTS

Levels of kynurenic acid were reduced and quinolinic acid levels were raised in hippocampal samples from MTLE-HS patients, whereas kynurenine levels remained unaltered, compared with levels in non-seizure controls. Spontaneous glutamatergic activity in MTLE-HS hippocampal samples was higher than that in non-seizure controls. Treatment with kynurenine inhibited glutamatergic activity in non-seizure control samples but not in MTLE-HS samples. However, exogenously applied kynurenic acid inhibited glutamatergic activity in both non-seizure control and MTLE-HS hippocampal samples. Also, levels of kynurenine aminotransferase II and its cofactor pyridoxal phosphate were reduced in MTLE-HS samples.

CONCLUSION AND IMPLICATIONS

Our findings indicate that altered metabolism of tryptophan-kynurenine pathway metabolites in hippocampus could contribute to hyperglutamatergic tone in patients with MTLE-HS.

Coupling of Co-expression Network Analysis and Machine Learning Validation Unearthed Potential Key Genes Involved in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an incurable disease that afflicts 0.5–1.0% of the global population though it is less threatening at its early stage. Therefore, improved diagnostic efficiency and prognostic outcome are critical for confronting RA. Although machine learning is considered a promising technique in clinical research, its potential in verifying the biological significance of gene was not fully exploited. The performance of a machine learning model depends greatly on the features used for model training; therefore, the effectiveness of prediction might reflect the quality of input features. In the present study, we used weighted gene co-expression network analysis (WGCNA) in conjunction with differentially expressed gene (DEG) analysis to select the key genes that were highly associated with RA phenotypes based on multiple microarray datasets of RA blood samples, after which they were used as features in machine learning model validation. A total of six machine learning models were used to validate the biological significance of the key genes based on gene expression, among which five models achieved good performances [area under curve (AUC) >0.85], suggesting that our currently identified key genes are biologically significant and highly representative of genes involved in RA. Combined with other biological interpretations including Gene Ontology (GO) analysis, protein–protein interaction (PPI) network analysis, as well as inference of immune cell composition, our current study might shed a light on the in-depth study of RA diagnosis and prognosis.

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.

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.

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.

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.

Intellectual Disability Associated With Pyridoxine-Responsive Epilepsies: The Need to Protect Cognitive Development

Pyridoxine (vitamin B6)-responsive epilepsies are severe forms of epilepsy that manifest as seizures immediately after birth, sometimes in utero, sometimes months, or years after birth. Seizures may be treated efficiently by life-long supplementation with pyridoxine or its biologically active form, pyridoxal phosphate, but even so patients may become intellectually disabled, for which there currently is no effective treatment. The condition may be caused by mutations in several genes (TNSALP, PIGV, PIGL, PIGO, PNPO, PROSC, ALDH7A1, MOCS2, or ALDH4A1). Mutations in ALDH7A1, MOCS2, and ALDH4A1 entail build-up of reactive aldehydes (α-aminoadipic semialdehyde, γ-glutamic semialdehyde) that may react non-enzymatically with macromolecules of brain cells. Such reactions may alter the function of macromolecules, and they may produce "advanced glycation end products" (AGEs). AGEs trigger inflammation in the brain. This understanding points to aldehyde-quenching, anti-AGE, or anti-inflammatory therapies as possible strategies to protect cognitive development and prevent intellectual disability in affected children. Studies on how aldehydes traverse cell membranes and how they affect brain function could further the development of therapies for patients with pyridoxine-responsive epilepsies.

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.

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.