Mutations in antiquitin in individuals with pyridoxine-dependent seizures

High sensitivity HPLC method for determination of the allysine concentration in tissue by use of a naphthol derivative

Common to all fibrotic and metastatic diseases is the uncontrollable remodeling of tissue that leads to the accumulation of fibrous connective tissue components such as collagen and elastin. Build-up of fibrous tissue occurs through the cross-linking of collagen or elastin monomers, which is initiated through the oxidation of lysine residues to form α-aminoadipic-δ-semialdehyde (allysine). To provide a measure of the extent of collagen oxidation in disease models of fibrosis or metastasis, a rapid, sensitive HPLC method was developed to quantify the amount of allysine present in tissue. Allysine was reacted with sodium 2-naphthol-7-sulfonate under conditions typically applied for acid hydrolysis of tissues (6M HCl, 110°C, 24h) to prepare AL-NP, a fluorescent bis-naphthol derivative of allysine. High performance liquid chromatography was applied for analysis of allysine content. Under optimal reaction and detection conditions, successful separation of AL-NP was achieved with excellent analytical performance attained. Good linear relationship (R²=0.994) between peak area and concentration for AL-NP was attained for 0.35-175pmol of analyte. A detection limit of 0.02pmol in the standard sample with a 20μL injection was achieved for AL-NP, with satisfactory recovery from 88 to 100% determined. The method was applied in the quantification of allysine in healthy and fibrotic mouse lung tissue, with the fibrotic tissue showing a 2.5 fold increase in the content of allysine.

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.

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.

Clinical and genetic characteristics of pyridoxine-dependent epilepsy: Case series report of three Chinese patients with phenotypic variability

Pyridoxine-dependent epilepsy (PDE) is a rare disorder caused by aldehyde dehydrogenase 7 family member A1 (ALDH7A1) deficiency. The present study reported on three Chinese cases of PDE with phenotypic variability for providing further insight into this disease. All three patients presented with recurrent seizures and readily responded to treatment with pyridoxine, in line with the typical symptomology of PDE. The three cases varied in their clinical manifestations with regard to the time of onset, seizure type, EEG findings and mental development. Four ALDH7A1 mutations were identified in Case 1 (c.1008+1G>A and c.871+5G>A) and Case 2 (c.977A>G and c.1463A>G). To the best of our knowledge, the present study was the first to report on the mutations c.871+5G>A and c.1463A>G. Early definitive diagnosis and timely treatment with pyridoxine was the cornerstone of management of PDE. Timely treatment was associated with excellent prognosis. A high index of suspicion in cases and early genetic testing may facilitate early diagnosis of this rare disease.

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.

The role of genetic testing in epilepsy diagnosis and management

INTRODUCTION

Epilepsy is a common neurological disorder characterized by recurrent unprovoked seizures. More than 500 epilepsy-associated genes have been described in the literature. Most of these genes play an important role in neuronal excitability, cortical development or synaptic transmission. A growing number of genetic variations have implications on diagnosis and prognostic or therapeutic advice in terms of a personalized medicine. Area covered: The review presents the different forms of genetic epilepsies with respect to their underlying genetic and functional pathophysiology and aims to give advice for recommended genetic testing. Moreover, it discusses ethical and legal guidelines, costs and technical limitations which should be considered. Expert commentary: Genetic testing is an important component in the diagnosis and treatment of many forms of epilepsy.

Longevity of major coenzymes allows minimal de novo synthesis in microorganisms

Coenzymes are vital for cellular metabolism and act on the full spectrum of enzymatic reactions. Intrinsic chemical reactivity, enzyme promiscuity and high flux through their catalytic cycles make coenzymes prone to damage. To counteract such compromising factors and ensure stable levels of functional coenzymes, cells use a complex interplay between de novo synthesis, salvage, repair and degradation. However, the relative contribution of these factors is currently unknown, as is the overall stability of coenzymes in the cell. Here, we use dynamic ¹³C-labelling experiments to determine the half-life of major coenzymes of Escherichia coli. We find that coenzymes such as pyridoxal 5-phosphate, flavins, nicotinamide adenine dinucleotide (phosphate) and coenzyme A are remarkably stable in vivo and allow biosynthesis close to the minimal necessary rate. In consequence, they are essentially produced to compensate for dilution by growth and passed on over generations of cells. Exceptions are antioxidants, which are short-lived, suggesting an inherent requirement for increased renewal. Although the growth-driven turnover of stable coenzymes is apparently subject to highly efficient end-product homeostasis, we exemplify that coenzyme pools are propagated in excess in relation to actual growth requirements. Additional testing of Bacillus subtilis and Saccharomyces cerevisiae suggests that coenzyme longevity is a conserved feature in biology.

Phenotype, biochemical features, genotype and treatment outcome of pyridoxine-dependent epilepsy

We report treatment outcome of eleven patients with pyridoxine-dependent epilepsy caused by pathogenic variants in ALDH7A1 (PDE-ALDH7A1). We developed a clinical severity score to compare phenotype with biochemical features, genotype and delays in the initiation of pyridoxine. Clinical severity score included 1) global developmental delay/ intellectual disability; 2) age of seizure onset prior to pyridoxine; 3) current seizures on treatment. Phenotype scored 1-3 = mild; 4-6 = moderate; and 7-9 = severe. Five patients had mild, four patients had moderate, and two patients had severe phenotype. Phenotype ranged from mild to severe in eight patients (no lysine-restricted diet in the infantile period) with more than 10-fold elevated urine or plasma α-AASA levels. Phenotype ranged from mild to moderate in patients with homozygous truncating variants and from moderate to severe in patients with homozygous missense variants. There was no correlation between severity of the phenotype and the degree of α-AASA elevation in urine or genotype. All patients were on pyridoxine, nine patients were on arginine and five patients were on the lysine-restricted diet. 73% of the patients became seizure free on pyridoxine. 25% of the patients had a mild phenotype on pyridoxine monotherapy. Whereas, 100% of the patients, on the lysine-restricted diet initiated within their first 7 months of life, had a mild phenotype. Early initiation of lysine-restricted diet and/or arginine therapy likely improved neurodevelopmental outcome in young patients with PDE-ALDH7A1.

A Model Program for Translational Medicine in Epilepsy Genetics

Recent technological advances in gene sequencing have led to a rapid increase in gene discovery in epilepsy. However, the ability to assess pathogenicity of variants, provide functional analysis, and develop targeted therapies has not kept pace with rapid advances in sequencing technology. Thus, although clinical genetic testing may lead to a specific molecular diagnosis for some patients, test results often lead to more questions than answers. As the field begins to focus on therapeutic applications of genetic diagnoses using precision medicine, developing processes that offer more than equivocal test results is essential. The success of precision medicine in epilepsy relies on establishing a correct genetic diagnosis, analyzing functional consequences of genetic variants, screening potential therapeutics in the preclinical laboratory setting, and initiating targeted therapy trials for patients. The authors describe the structure of a comprehensive, pediatric Epilepsy Genetics Program that can serve as a model for translational medicine in epilepsy.

Impact of disease-Linked mutations targeting the oligomerization interfaces of aldehyde dehydrogenase 7A1

Aldehyde dehydrogenase 7A1 (ALDH7A1) is involved in lysine catabolism, catalyzing the oxidation of α-aminoadipate semialdehyde to α-aminoadipate. Certain mutations in the ALDH7A1 gene, which are presumed to reduce catalytic activity, cause an autosomal recessive seizure disorder known as pyridoxine-dependent epilepsy (PDE). Although the genetic association between ALDH7A1 and PDE is well established, little is known about the impact of PDE-mutations on the structure and catalytic function of the enzyme. Herein we report the first study of the molecular consequences of PDE mutations using purified ALDH7A1 variants. Eight variants, with mutations in the oligomer interfaces, were expressed in Escherichia coli: P78L, G83E, A129P, G137V, G138V, A149E, G255D, and G263E. All but P78L and G83E were soluble and could be purified. All six soluble mutants were catalytically inactive. The impact of the mutations on oligomerization was assessed by analytical ultracentrifugation. Wild-type ALDH7A1 is shown to exist in a dimer-tetramer equilibrium with a dissociation constant of 16 μM. In contrast to the wild-type enzyme, the variants reside in monomer-dimer equilibria and are apparently incapable of forming a tetrameric species, even at high enzyme concentration. The available evidence suggests that they are misfolded assemblies lacking the three-dimensional structure required for catalysis.

Pharmacogenomics in epilepsy

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Genetic variation can influence response to antiepileptic drug (AED) treatment through various effector processes.

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Metabolism of many AEDs is mediated by the cytochrome P450 (CYP) family; some of the CYPs have allelic variants that may affect serum AED concentrations.

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‘Precision medicine’ focuses on the identification of an underlying genetic aetiology allowing personalised therapeutic choices.

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Certain human leukocyte antigen, HLA, alleles are associated with an increased risk of idiosyncratic adverse drug reactions.

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New results are emerging from large-scale multinational efforts, likely imminently to add knowledge of value from a pharmacogenetic perspective.

There is high variability in the response to antiepileptic treatment across people with epilepsy. Genetic factors significantly contribute to such variability. Recent advances in the genetics and neurobiology of the epilepsies are establishing the basis for a new era in the treatment of epilepsy, focused on each individual and their specific epilepsy. Variation in response to antiepileptic drug treatment may arise from genetic variation in a range of gene categories, including genes affecting drug pharmacokinetics, and drug pharmacodynamics, but also genes held to actually cause the epilepsy itself.

From a purely pharmacogenetic perspective, there are few robust genetic findings with established evidence in epilepsy. Many findings are still controversial with anecdotal or less secure evidence and need further validation, e.g. variation in genes for transporter systems and antiepileptic drug targets. The increasing use of genetic sequencing and the results of large-scale collaborative projects may soon expand the established evidence.

Precision medicine treatments represent a growing area of interest, focussing on reversing or circumventing the pathophysiological effects of specific gene mutations. This could lead to a dramatic improvement of the effectiveness and safety of epilepsy treatments, by targeting the biological mechanisms responsible for epilepsy in each specific individual.

Whilst much has been written about epilepsy pharmacogenetics, there does now seem to be building momentum that promises to deliver results of use in clinic.

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.

[Intermittent convulsions for 1.5 years and psychomotor retardation in a girl]

The study reports a girl with pyridoxine-dependent epilepsy. The girl was admitted at the age of 2 years because of intermittent convulsions for 1.5 years and psychomotor retardation. She had a history of "hypoxia" in the neonatal period. At the age of 5 months recurrent epileptic seizures occurred. The child was resistant to antiepileptic drugs, and had many more seizures when she got cold or fever. She also had a lot of convulsive status epilepticus. No discharges were found during several video-EEG monitorings. Cerebral MRI examinations showed normal results. So Dravet syndrome was clinically suspected. ALDH7N1 gene mutation analysis revealed two heterozygote mutations, and pyridoxine-dependent epilepsy was thus confirmed. Seizures were generally controlled after pyridoxine supplementation.

Mutations in PROSC Disrupt Cellular Pyridoxal Phosphate Homeostasis and Cause Vitamin-B6-Dependent Epilepsy

Pyridoxal 5'-phosphate (PLP), the active form of vitamin B₆, functions as a cofactor in humans for more than 140 enzymes, many of which are involved in neurotransmitter synthesis and degradation. A deficiency of PLP can present, therefore, as seizures and other symptoms that are treatable with PLP and/or pyridoxine. Deficiency of PLP in the brain can be caused by inborn errors affecting B₆ vitamer metabolism or by inactivation of PLP, which can occur when compounds accumulate as a result of inborn errors of other pathways or when small molecules are ingested. Whole-exome sequencing of two children from a consanguineous family with pyridoxine-dependent epilepsy revealed a homozygous nonsense mutation in proline synthetase co-transcribed homolog (bacterial), PROSC, which encodes a PLP-binding protein of hitherto unknown function. Subsequent sequencing of 29 unrelated indivduals with pyridoxine-responsive epilepsy identified four additional children with biallelic PROSC mutations. Pre-treatment cerebrospinal fluid samples showed low PLP concentrations and evidence of reduced activity of PLP-dependent enzymes. However, cultured fibroblasts showed excessive PLP accumulation. An E.coli mutant lacking the PROSC homolog (ΔYggS) is pyridoxine sensitive; complementation with human PROSC restored growth whereas hPROSC encoding p.Leu175Pro, p.Arg241Gln, and p.Ser78Ter did not. PLP, a highly reactive aldehyde, poses a problem for cells, which is how to supply enough PLP for apoenzymes while maintaining free PLP concentrations low enough to avoid unwanted reactions with other important cellular nucleophiles. Although the mechanism involved is not fully understood, our studies suggest that PROSC is involved in intracellular homeostatic regulation of PLP, supplying this cofactor to apoenzymes while minimizing any toxic side reactions.

Pyridoxine-dependent epilepsy: report on three families with neuropathology

Pyridoxine-dependent epilepsy (PDE) is a pharmacoresistant epileptogenic encephalopathy controlled by pyridoxine supplementation at pharmacological doses. Despite supplementation, the long-term outcome is often poor possibly because of recurrent seizures and developmental structural brain abnormalities. We report on five patients with PDE from three unrelated families. The diagnosis was confirmed by ALDH7A1 sequencing, which allowed for the characterization of two homozygous variations [NM_001182.3:c.1279G > C - p.(Glu427Gln) and c.834G > A - p.(Val278Val)]. Brain autopsy was conducted for one untreated patient with molecularly confirmed antiquitin deficiency. Macroscopic and histological examination revealed a combination of lesions resulting from recurrent seizures and consisting of extensive areas of cortical necrosis, gliosis, and hippocampic sclerosis. The examination also revealed developmental abnormalities including corpus callosum dysgenesis and corticospinal pathfinding anomalies. This case is the second to be reported in the literature, and our findings show evidence that antiquitin is required for normal brain development and functioning. Despite prophylactic prenatal pyridoxine supplementation during the last trimester of pregnancy in one of the three families and sustained pyridoxine treatment in three living patients, the clinical outcome remained poor with delayed acquisition of neurocognitive skills. Combined therapy (pyridoxine/arginine supplementation and lysine-restricted diet) should be considered early in the course of the disease for a better long-term outcome. Enhanced knowledge of PDE features is required to improve treatment strategies.

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.

Lysine Restriction and Pyridoxal Phosphate Administration in a NADK2 Patient

We report the case of a 10-year-old Spanish girl with mutations in NADK2 Prenatal central nervous system abnormalities showed ventriculomegaly, colpocephaly, and hypoplasia of the corpus callosum. At birth, axial hypotonia, uncoordinated movements, microcephaly, and generalized cerebellar atrophy were detected. Metabolic investigations revealed high lysine, lactate, and pipecolic acid levels in blood and cerebrospinal fluid. Pyruvate carboxylase and pyruvate dehydrogenase activity in fibroblasts were normal. Beginning at birth she received biotin, thiamine, and carnitine supplementation. A lysine-restricted diet was started when she was 1 month old. Because pipecolic acid was high, pyridoxine was added to treatment. At 3 years old, astatic myoclonic epilepsy appeared, with no response to levetiracetam. We switched pyridoxine to pyridoxal phosphate, with electroclinical improvement. Because the activity of mitochondrial respiratory chain complexes III and IV was slightly low in muscle, other cofactors such as ubidecarenone, idebenone, vitamin E, and creatine were added to the treatment. At 8 years old, plasma acylcarnitine testing was performed, and high levels of 2-trans, 4-cis-decadienoylcarnitine were found. Whole exome sequencing identified a homozygous splice site mutation in NADK2 (c.956+6T>C; p.Trp319Cysfs*21). This substitution generates exon skipping, leading to a truncated protein. In fact, NADK2 messenger RNA and the corresponding protein were almost absent. Now, at 10 years of age she presents with ataxia and incoordination. She has oromotor dysphasia but is able to understand fluid language and is a very friendly girl. We hypothesize that the patient's clinical improvement could be due to her lysine-restricted diet together with cofactors and pyridoxal phosphate administration.

Effects of a Mutation in the HSPE1 Gene Encoding the Mitochondrial Co-chaperonin HSP10 and Its Potential Association with a Neurological and Developmental Disorder

We here report molecular investigations of a missense mutation in the HSPE1 gene encoding the HSP10 subunit of the HSP60/ HSP10 chaperonin complex that assists protein folding in the mitochondrial matrix. The mutation was identified in an infant who came to clinical attention due to infantile spasms at 3 months of age. Clinical exome sequencing revealed heterozygosity for a HSPE1 NM_002157.2:c.217C>T de novo mutation causing replacement of leucine with phenylalanine at position 73 of the HSP10 protein. This variation has never been observed in public exome sequencing databases or the literature. To evaluate whether the mutation may be disease-associated we investigated its effects by in vitro and ex vivo studies. Our in vitro studies indicated that the purified mutant protein was functional, yet its thermal stability, spontaneous refolding propensity, and resistance to proteolytic treatment were profoundly impaired. Mass spectrometric analysis of patient fibroblasts revealed barely detectable levels of HSP10-p.Leu73Phe protein resulting in an almost 2-fold decrease of the ratio of HSP10 to HSP60 subunits. Amounts of the mitochondrial superoxide dismutase SOD2, a protein whose folding is known to strongly depend on the HSP60/HSP10 complex, were decreased to approximately 20% in patient fibroblasts in spite of unchanged SOD2 transcript levels. As a likely consequence, mitochondrial superoxide levels were increased about 2-fold. Although, we cannot exclude other causative or contributing factors, our experimental data support the notion that the HSP10-p.Leu73Phe mutation could be the cause or a strong contributing factor for the disorder in the described patient.

Epileptic Encephalopathy in Childhood: A Stepwise Approach for Identification of Underlying Genetic Causes

Epilepsy is one of the most common neurological disorders in childhood. Epilepsy associated with global developmental delay and cognitive dysfunction is defined as epileptic encephalopathy. Certain inherited metabolic disorders presenting with epileptic encephalopathy can be treated with disease specific diet, vitamin, amino acid or cofactor supplementations. In those disorders, disease specific therapy is successful to achieve good seizure control and improve long-term neurodevelopmental outcome. For this reason, intractable epilepsy with global developmental delay or history of developmental regression warrants detailed metabolic investigations for the possibility of an underlying treatable inherited metabolic disorder, which should be undertaken as first line investigations. An underlying genetic etiology in epileptic encephalopathy has been supported by recent studies such as array comparative genomic hybridization, targeted next generation sequencing panels, whole exome and whole genome sequencing. These studies report a diagnostic yield up to 70%, depending on the applied genetic testing as well as number of patients enrolled. In patients with epileptic encephalopathy, a stepwise approach for diagnostic work-up will help to diagnose treatable inherited metabolic disorders quickly. Application of detailed genetic investigations such as targeted next generation sequencing as second line and whole exome sequencing as third line testing will diagnose underlying genetic disease which will help for genetic counseling as well as guide for prenatal diagnosis. Knowledge of underlying genetic cause will provide novel insights into the pathogenesis of epileptic encephalopathy and pave the ground towards the development of targeted neuroprotective treatment strategies to improve the health outcome of children with epileptic encephalopathy.

Regulation of post-Golgi LH3 trafficking is essential for collagen homeostasis

Post-translational modifications are necessary for collagen precursor molecules (procollagens) to acquire final shape and function. However, the mechanism and contribution of collagen modifications that occur outside the endoplasmic reticulum and Golgi are not understood. We discovered that VIPAR, with its partner proteins, regulate sorting of lysyl hydroxylase 3 (LH3, also known as PLOD3) into newly identified post-Golgi collagen IV carriers and that VIPAR-dependent sorting is essential for modification of lysines in multiple collagen types. Identification of structural and functional collagen abnormalities in cells and tissues from patients and murine models of the autosomal recessive multisystem disorder Arthrogryposis, Renal dysfunction and Cholestasis syndrome caused by VIPAR and VPS33B deficiencies confirmed our findings. Thus, regulation of post-Golgi LH3 trafficking is essential for collagen homeostasis and for the development and function of multiple organs and tissues.

Effect of dietary lysine restriction and arginine supplementation in two patients with pyridoxine-dependent epilepsy

Pyridoxine-Dependent Epilepsy (PDE) is a recessive disorder caused by deficiency of α-aminoadipic semialdehyde dehydrogenase in the catabolic pathway of lysine. It is characterized by intractable seizures controlled by the administration of pharmacological doses of vitamin B6. Despite seizure control with pyridoxine, intellectual disability and developmental delays are still observed in some patients with PDE, likely due to the accumulation of toxic intermediates in the lysine catabolic pathway: alpha-aminoadipic semialdehyde (AASA), delta-1-piperideine-6-carboxylate (P6C), and pipecolic acid. Here we evaluate biochemical and clinical parameters in two PDE patients treated with a lysine-restricted diet and arginine supplementation (100-150mg/kg), aimed at reducing the levels of PDE biomarkers. Lysine restriction resulted in decreased accumulation of PDE biomarkers and improved development. Plasma lysine but not plasma arginine, directly correlated with plasma levels of AASA-P6C (p<0.001, r(2)=0.640) and pipecolic acid (p<0.01, r(2)=0.484). In addition, plasma threonine strongly correlated with the levels of AASA-P6C (p<0.0001, r(2)=0.732) and pipecolic acid (p<0.005, r(2)=0.527), suggesting extreme sensitivity of threonine catabolism to pyridoxine availability. Our results further support the use of dietary therapies in combination with pyridoxine for the treatment of PDE.

A Prospective Case Study of the Safety and Efficacy of Lysine-Restricted Diet and Arginine Supplementation Therapy in a Patient With Pyridoxine-Dependent Epilepsy Caused by Mutations in ALDH7A1

BACKGROUND

Pyridoxine-dependent epilepsy (PDE) is caused by mutations in ALDH7A1 (PDE-ALDH7A1), which encodes α-aminoadipic semialdehyde dehydrogenase in the lysine catabolic pathway, resulting in accumulation of α-aminoadipic-acid-semialdehyde.

PATIENT DESCRIPTION AND RESULTS

We present a three-year treatment outcome of a child with PDE-ALDH7A1 on pyridoxine (started at age three weeks of age), lysine-restricted diet (started at age seven months), and arginine supplementation therapy (started at age 26 months). He had a markedly elevated urinary α-aminoadipic-acid-semialdehyde (39.6 mmol/mol of creatinine; reference range = 0 to 2) and compound heterozygous mutations in ALDH7A1 (c.446C>A and c.919C>T). He has been seizure free since the age three weeks. He achieved normal cognitive function at age 3.5 years. He exhibited gross motor delay after the age 13 months. Tryptophan supplementation was added for the mild cerebral serotonin deficiency at the thirteenth month of therapy. Arginine supplementation was added to achieve further decrease in the cerebrospinal fluid α-aminoadipic-acid-semialdehyde levels at the 26th month of therapy. His cerebrospinal fluid α-aminoadipic-acid-semialdehyde levels were markedly decreased on this combined therapy.

CONCLUSIONS

This treatment was well tolerated. Mild cerebral serotonin deficiency was the only biochemical effect with no clinical features. Despite excellent compliance and strict treatment regimen, cerebrospinal fluid α-aminoadipic-acid-semialdehyde levels did not normalize.

Nicotinamide Cofactors Suppress Active-Site Labeling of Aldehyde Dehydrogenases

Active site labeling by (re)activity-based probes is a powerful chemical proteomic tool to globally map active sites in native proteomes without using substrates. Active site labeling is usually taken as a readout for the active state of the enzyme because labeling reflects the availability and reactivity of active sites, which are hallmarks for enzyme activities. Here, we show that this relationship holds tightly, but we also reveal an important exception to this rule. Labeling of Arabidopsis ALDH3H1 with a chloroacetamide probe occurs at the catalytic Cys, and labeling is suppressed upon nitrosylation and oxidation, and upon treatment with other Cys modifiers. These experiments display a consistent and strong correlation between active site labeling and enzymatic activity. Surprisingly, however, labeling is suppressed by the cofactor NAD(+), and this property is shared with other members of the ALDH superfamily and also detected for unrelated GAPDH enzymes with an unrelated hydantoin-based probe in crude extracts of plant cell cultures. Suppression requires cofactor binding to its binding pocket. Labeling is also suppressed by ALDH modulators that bind at the substrate entrance tunnel, confirming that labeling occurs through the substrate-binding cavity. Our data indicate that cofactor binding adjusts the catalytic Cys into a conformation that reduces the reactivity toward chloroacetamide probes.

The Pivotal Role of Aldehyde Toxicity in Autism Spectrum Disorder: The Therapeutic Potential of Micronutrient Supplementation

Autism spectrum disorder (ASD) is characterized by social and communication impairments as well as by restricted, repetitive patterns of behavior and interests. Genomic studies have not revealed dominant genetic errors common to all forms of ASD. So ASD is assumed to be a complex disorder due to mutations in hundreds of common variants. Other theories argue that spontaneous DNA mutations and/or environmental factors contribute to as much as 50% of ASD. In reviewing potential genetic linkages between autism and alcoholism, it became apparent that all theories of ASD are consistent with aldehyde toxicity, in which endogenous and exogenous aldehydes accumulate as a consequence of mutations in key enzymes. Aldehyde toxicity is characterized by cell-localized, micronutrient deficiencies in sulfur-containing antioxidants, thiamine (B1), pyridoxine (B6), folate, Zn²⁺, possibly Mg²⁺, and retinoic acid, causing oxidative stress and a cascade of metabolic disturbances. Aldehydes also react with selective cytosolic and membrane proteins in the cell of origin; then some types migrate to damage neighboring cells. Reactive aldehydes also form adducts with DNA, selectively mutating bases and inducing strand breakage. This article reviews the relevant genomic, biochemical, and nutritional literature, which supports the central hypothesis that most ASD symptoms are consistent with symptoms of aldehyde toxicity. The hypothesis represents a paradigm shift in thinking and has profound implications for clinical detection, treatment, and even prevention of ASD. Insight is offered as to which neurologically afflicted children might successfully be treated with micronutrients and which children are unlikely to be helped. The aldehyde toxicity hypothesis likely applies to other neurological disorders.

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.

Impaired PLP-dependent metabolism in brain samples from Huntington disease patients and transgenic R6/1 mice

Oxidative stress has been described as important to Huntington disease (HD) progression. In a previous HD study, we identified several carbonylated proteins, including pyridoxal kinase and antiquitin, both of which are involved in the metabolism of pyridoxal 5´-phosphate (PLP), the active form of vitamin B6. In the present study, pyridoxal kinase levels were quantified and showed to be decreased both in HD patients and a R6/1 mouse model, compared to control samples. A metabolomic analysis was used to analyze metabolites in brain samples of HD patients and R6/1 mice, compared to control samples using mass spectrometry. This technique allowed detection of increased concentrations of pyridoxal, the substrate of pyridoxal kinase. In addition, PLP, the product of the reaction, was decreased in striatum from R6/1 mice. Furthermore, glutamate and cystathionine, both substrates of PLP-dependent enzymes were increased in HD. This reinforces the hypothesis that PLP synthesis is impaired, and could explain some alterations observed in the disease. Together, these results identify PLP as a potential therapeutic agent.

Neuropathological Mechanisms of Seizures in Autism Spectrum Disorder

This manuscript reviews biological abnormalities shared by autism spectrum disorder (ASD) and epilepsy. Two neuropathological findings are shared by ASD and epilepsy: abnormalities in minicolumn architecture and γ-aminobutyric acid (GABA) neurotransmission. The peripheral neuropil, which is the region that contains the inhibition circuits of the minicolumns, has been found to be decreased in the post-mortem ASD brain. ASD and epilepsy are associated with inhibitory GABA neurotransmission abnormalities including reduced GABA_A and GABA_B subunit expression. These abnormalities can elevate the excitation-to-inhibition balance, resulting in hyperexcitablity of the cortex and, in turn, increase the risk of seizures. Medical abnormalities associated with both epilepsy and ASD are discussed. These include specific genetic syndromes, specific metabolic disorders including disorders of energy metabolism and GABA and glutamate neurotransmission, mineral and vitamin deficiencies, heavy metal exposures and immune dysfunction. Many of these medical abnormalities can result in an elevation of the excitatory-to-inhibitory balance. Fragile X is linked to dysfunction of the mGluR5 receptor and Fragile X, Angelman and Rett syndromes are linked to a reduction in GABA_A receptor expression. Defects in energy metabolism can reduce GABA interneuron function. Both pyridoxine dependent seizures and succinic semialdehyde dehydrogenase deficiency cause GABA deficiencies while urea cycle defects and phenylketonuria cause abnormalities in glutamate neurotransmission. Mineral deficiencies can cause glutamate and GABA neurotransmission abnormalities and heavy metals can cause mitochondrial dysfunction which disrupts GABA metabolism. Thus, both ASD and epilepsy are associated with similar abnormalities that may alter the excitatory-to-inhibitory balance of the cortex. These parallels may explain the high prevalence of epilepsy in ASD and the elevated prevalence of ASD features in individuals with epilepsy.

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.

Toward precision medicine in neurological diseases

Technological development has paved the way for accelerated genomic discovery and is bringing precision medicine into view. The goal of precision medicine is to deliver optimally targeted and timed interventions tailored to an individual's molecular drivers of disease. Neurological diseases are promisingly suited models for precision medicine because of the rapidly expanding genetic knowledge base, phenotypic classification, the development of biomarkers and the potential modifying treatments. Moving forward, it is crucial that through these integrated research platforms to provide analysis both for accurate personal genome analysis and gene and drug discovery. Here we describe our vision of how precision medicine can bring greater clarity to the clinical and biological complexity of neurological diseases.

The Regulation of Essential Amino Acid Synthesis and Accumulation in Plants

Although amino acids are critical for all forms of life, only proteogenic amino acids that humans and animals cannot synthesize de novo and therefore must acquire in their diets are classified as essential. Nine amino acids-lysine, methionine, threonine, phenylalanine, tryptophan, valine, isoleucine, leucine, and histidine-fit this definition. Despite their nutritional importance, several of these amino acids are present in limiting quantities in many of the world's major crops. In recent years, a combination of reverse genetic and biochemical approaches has been used to define the genes encoding the enzymes responsible for synthesizing, degrading, and regulating these amino acids. In this review, we describe recent advances in our understanding of the metabolism of the essential amino acids, discuss approaches for enhancing their levels in plants, and appraise efforts toward their biofortification in crop plants.

Evidence that COG0325 proteins are involved in PLP homeostasis

Pyridoxal 5'-phosphate (PLP) is an essential cofactor for nearly 60 Escherichia coli enzymes but is a highly reactive molecule that is toxic in its free form. How PLP levels are regulated and how PLP is delivered to target enzymes are still open questions. The COG0325 protein family belongs to the fold-type III class of PLP enzymes and binds PLP but has no known biochemical activity although it occurs in all kingdoms of life. Various pleiotropic phenotypes of the E. coli COG0325 (yggS) mutant have been reported, some of which were reproduced and extended in this study. Comparative genomic, genetic and metabolic analyses suggest that these phenotypes reflect an imbalance in PLP homeostasis. The E. coli yggS mutant accumulates the PLP precursor pyridoxine 5'-phosphate (PNP) and is sensitive to an excess of pyridoxine but not of pyridoxal. The pyridoxine toxicity phenotype is complemented by the expression of eukaryotic yggS orthologs. It is also suppressed by the presence of amino acids, specifically isoleucine, threonine and leucine, suggesting the PLP-dependent enzyme transaminase B (IlvE) is affected. These genetic results lay a foundation for future biochemical studies of the role of COG0325 proteins in PLP homeostasis.

Inactive mutants of human pyridoxine 5'-phosphate oxidase: a possible role for a noncatalytic pyridoxal 5'-phosphate tight binding site

Pyridoxal 5'-phosphate (PLP) is a cofactor for many vitamin B6-requiring enzymes that are important for the synthesis of neurotransmitters. Pyridoxine 5'-phosphate oxidase (PNPO) is one of two enzymes that produce PLP. Some 16 known mutations in human PNPO (hPNPO), including R95C and R229W, lead to deficiency of PLP in the cell and have been shown to cause neonatal epileptic encephalopathy (NEE). This disorder has no effective treatment, and is often fatal unless treated with PLP. In this study, we show that R95C hPNPO exhibits a 15-fold reduction in affinity for the FMN cofactor, a 71-fold decrease in affinity for the substrate PNP, a 4.9-fold decrease in specific activity, and a 343-fold reduction in catalytic activity, compared to the wild-type enzyme. We have reported similar findings for R229W hPNPO. This report also shows that wild-type, R95C and R229W hPNPO bind PLP tightly at a noncatalytic site and transfer it to activate an apo-B6 enzyme into the catalytically active holo-form. We also show for the first time that hPNPO forms specific interactions with several B6 enzymes with dissociation constants ranging from 0.3 to 12.3 μm. Our results suggest a possible in vivo role for the tight binding of PLP in hPNPO, whether wild-type or variant, by protecting the very reactive PLP, and transferring this PLP directly to activate apo-B6 enzymes.

A novel method for simultaneous quantification of alpha-aminoadipic semialdehyde/piperideine-6-carboxylate and pipecolic acid in plasma and urine

OBJECTIVES

Elevated levels of pipecolic acid (PA), α-aminoadipic semialdehyde (AASA) and its cyclic form Δ1-piperideine-6-carboxylate (P6C) are characteristic of pyridoxine dependent epilepsy (PDE), a rare disorder of inborn error of metabolism. Recent studies showed the effectiveness of dietary therapy in PDE patients and emphasized the importance of the assessment of these metabolites for monitoring treatment efficacy. The objective of this study was to develop a robust and sensitive method for simultaneous quantification of AASA-P6C and PA in plasma and urine.

DESIGN AND METHODS

Plasma and urine samples were derivatized with 3N HCl in n-butanol (v/v) and injected onto ACQUITY BEH-C18 column. A gradient of water/methanol containing 0.1% formic acid was used for the chromatographic separation of AASA, P6C and PA. The analytes' concentrations were calculated using their calibration curves and the sum of AASA and P6C (AASA-P6C) was calculated. To evaluate the clinical utility of this test, samples from unaffected controls and patients with confirmed PDE were analyzed.

RESULTS

The performance characteristics of the assay as well as sample stability and interferences were determined. The intra- and inter- assay CVs were ≤2.9% and ≤10.9% for AASA-P6C, and ≤3.3% and ≤12.6% for PA, respectively. Reference ranges for AASA-P6C and PA in plasma and urine were established. Comparison of values obtained from unaffected controls and PDE patients showed high clinical sensitivity and specificity of the assay.

CONCLUSIONS

This novel method for the simultaneous quantification of AASA-P6C and PA in plasma and urine can be used in a clinical laboratory setting for the diagnosis and monitoring of patients with PDE.

Simultaneous detection of lysine metabolites by a single LC-MS/MS method: monitoring lysine degradation in mouse plasma

Detection and quantification of lysine degradation metabolites in plasma is necessary for the diagnosis and follow-up of diseases such as pyridoxine-dependent epilepsy. The principal metabolites involved in the disease are related to the first steps of lysine oxidation, either through the saccharopine or the pipecolate pathways. Currently, there are three different analytical methods used to assess the content of these metabolites in urine and plasma, but they require different sample preparations and analytical equipment. Here, we describe a protocol that calls for a simple sample preparation and uses liquid chromatography tandem mass spectrometry (LC–MS/MS) that allows simultaneous detection and quantification of underivatized l-saccharopine, l-aminoadipic acid, l-pipecolic acid, piperideine-6-carboxylate, l-glutamic acid, and pyridoxal-5-phosphate in plasma samples. To validate the method we analyzed the time course degradation after intraperitoneal injection of l-lysine in C57BL/6/J mice. We observed that the degradation of lysine through the saccharopine pathway reached a maximum within the first 2 h. At this time point there was an increase in the levels of the metabolites saccharopine, aminoadipic acid, and pipecolic acid by 3-, 24- and 3.4-fold, respectively, compared to time zero levels. These metabolites returned to basal levels after 4–6 h. In conclusion, we have developed a LC–MS/MS approach, which allows simultaneous analysis of lysine degradation metabolites without the need for derivatization.

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.

[Fundamental Properties of Aldehyde Dehydrogenase 2 (ALDH2) and the Importance of the ALDH2 Polymorphism]

Human aldehyde dehydrogenase 2 (ALDH2) is a 56 kDa mitochondrial protein that forms homodimers through hydrogen bonding interactions between the Glu487 and Arg475 residues of two ALDH2 proteins. Two ALDH2 homodimers can interact to form an ALDH2 tetramer. ALDH2 is widely distributed throughout the organs of the body. In addition to its dehydrogenase activity, ALDH2 also exhibits esterase and reductase activities, with the main substrates for these three activities being aldehydes, 4-nitrophenyl acetate and nitroglycerin, respectively. ALDH2 can be readily inhibited by a wide variety of endogenous and exogenous chemicals, but the induction or activation of this enzyme remains unlikely. The polymorphism of ALDH2 to the corresponding ALDH2*2 variant results in a severe deficiency in ALDH2 activity, and this particular polymorphism is prevalent among people of Mongoloid descent. It seems reasonable to expect that people with the ALDH2*2 variant would be more vulnerable to stress and diseases because ALDH2 defends the human body against toxic aldehydes. However, it has been suggested that people with the ALDH2*2 variant are protected by alternative stress-defending systems. The ALDH2*2 variant has been reported to be associated with many different kinds of diseases, although the mechanisms underlying these associations have not yet been elucidated. ALDH2 polymorphism has a significant impact on human health; further studies are therefore required to determine the practical implications of this polymorphism in the fields of preventive and clinical medicine.

Simultaneous detection of lysine metabolites by a single LC-MS/MS method: monitoring lysine degradation in mouse plasma

Detection and quantification of lysine degradation metabolites in plasma is necessary for the diagnosis and follow-up of diseases such as pyridoxine-dependent epilepsy. The principal metabolites involved in the disease are related to the first steps of lysine oxidation, either through the saccharopine or the pipecolate pathways. Currently, there are three different analytical methods used to assess the content of these metabolites in urine and plasma, but they require different sample preparations and analytical equipment. Here, we describe a protocol that calls for a simple sample preparation and uses liquid chromatography tandem mass spectrometry (LC-MS/MS) that allows simultaneous detection and quantification of underivatized l-saccharopine, l-aminoadipic acid, l-pipecolic acid, piperideine-6-carboxylate, l-glutamic acid, and pyridoxal-5-phosphate in plasma samples. To validate the method we analyzed the time course degradation after intraperitoneal injection of l-lysine in C57BL/6/J mice. We observed that the degradation of lysine through the saccharopine pathway reached a maximum within the first 2 h. At this time point there was an increase in the levels of the metabolites saccharopine, aminoadipic acid, and pipecolic acid by 3-, 24- and 3.4-fold, respectively, compared to time zero levels. These metabolites returned to basal levels after 4-6 h. In conclusion, we have developed a LC-MS/MS approach, which allows simultaneous analysis of lysine degradation metabolites without the need for derivatization.

A roadmap for precision medicine in the epilepsies

Technological advances have paved the way for accelerated genomic discovery and are bringing precision medicine clearly into view. Epilepsy research in particular is well suited to serve as a model for the development and deployment of targeted therapeutics in precision medicine because of the rapidly expanding genetic knowledge base in epilepsy, the availability of good in-vitro and in-vivo model systems to efficiently study the biological consequences of genetic mutations, the ability to turn these models into effective drug-screening platforms, and the establishment of collaborative research groups. Moving forward, it is crucial that these collaborations are strengthened, particularly through integrated research platforms, to provide robust analyses both for accurate personal genome analysis and gene and drug discovery. Similarly, the implementation of clinical trial networks will allow the expansion of patient sample populations with genetically defined epilepsy so that drug discovery can be translated into clinical practice.

Long-term outcome in pyridoxine-responsive infantile epilepsy

BACKGROUND

Dose regimens of pyridoxine (vitamin B6) for treatment of infantile spasms have varied from 200 mg/d to 300 mg/kg/d. Only two long-term outcome studies of the treated patients are available.

METHODS

We asked all pediatric neurologists treating pediatric epilepsy in Finland if they had seen patients with pyridoxine-responsive infantile epilepsy. Five children with infantile spasms and hypsarrhythmia and one with focal epilepsy were reported as pyridoxine responders. Data on clinical presentation and outcome were collected from patient charts.

RESULTS

All B6 responders had un-known aetiology. Two patients were studied for pyridoxal 5'-phosphate oxidase (PNPO) deficiency and showed negative results. Ages at seizure onset ranged from 4 to 7 months. The maintenance dose of oral pyridoxine was 150 mg/day. Response occurred within 1-to 14 days (mean 5 days). Two patients were treated with concomitant antiepileptic drugs. Duration of pyridoxine therapy varied from 6 weeks to 4 years (mean 26 months). Four patients had later seizure recurrence: one at 15 months with motor seizures (stopped by valproate), another two in adolescence with focal epilepsy and one at 20 years with unclassified epilepsy. Intelligence was normal in five patients and one had a mild mental deficiency. Follow-up ranged from 8.5 to 24 years.

CONCLUSIONS

Rare patients with infantile epilepsy but not pyridoxine dependency may respond to smaller doses of pyridoxine than reported before. Long-term cognitive outcome appears to be good but late seizure recurrence (in adolescence or in adulthood) occur. So far it is unknown if the response was determined by genetic traits or disease-related factors.

The saccharopine pathway in seed development and stress response of maize

Lysine is catabolized in developing plant tissues through the saccharopine pathway. In this pathway, lysine is converted into α-aminoadipic semialdehyde (AASA) by the bifunctional enzyme lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH). AASA is then converted into aminoadipic acid (AAA) by aminoadipic semialdehyde dehydrogenase (AASADH). Here, we show that LKR/SDH and AASADH are co-expressed in the sub-aleurone cell layers of the developing endosperm; however, although AASADH protein is produced in reproductive and vegetative tissues, the LKR/SDH protein is detectable only in the developing endosperm. AASADH showed an optimum pH of 7.4 and Kms for AASA and NAD(+) in the micromolar range. In the developing endosperm, the saccharopine pathway is induced by exogenous lysine and repressed by salt stress, whereas proline and pipecolic acid synthesis are significantly repressed by lysine. In young coleoptiles, the LKR/SDH and AASADH transcriptions are induced by abiotic stress, but while the AASADH protein accumulates in the stressed tissues, the LKR/SDH protein is not produced. In the developing seeds, the saccharopine pathway is used for pipecolic acid synthesis although proline may play a major role in abiotic stress response. The results indicate that the saccharopine pathway in maize seed development and stress responses significantly differ from that observed for dicot plants.

A cohort study of pyridoxine-dependent epilepsy and high prevalence of splice site IVS11+1G>A mutation in Chinese patients

PURPOSE

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder caused by mutations of the ALDH7A1 gene. We aimed to analyze the relations between the clinical diagnosis and treatment of PDE and ALDH7A1 gene mutations in Chinese PDE patients.

METHODS

The clinical manifestations, diagnosis and treatment were observed in a cohort of PDE patients with early onset of seizure. Video-electroencephalogram (VEEG) and magnetic resonance imaging (MRI) were performed. The mutation of ALDH7A1 gene was analyzed.

RESULTS

Of eight patients, six were males and two were females. Age of seizure onset ranged from 1 to 100 days and 75% patients presented with seizures in the neonatal period. All patients showed different degrees of developmental delay. EEGs showed focal or multifocal discharges, or were normal. Molecular analysis revealed 10 ALDH7A1 mutations, including 2 splice site mutations. Five patients had mutation at IVS11+1G>A site, six patients had missense mutations, one with nonsense mutation and another patient had 9-bp genomic deletion mutation. Among them, two mutations were first time reported.

CONCLUSIONS

Seizure onset was in neonatal or early infantile period in our PDE patients. Early recognition and diagnosis of the disease is necessary for early intervention and improve cognitive development in the later life. In this study, on the molecular level, we also identified the splice site mutation IVS11+1G>A as a high prevalence mutation site with a frequency of 31.25% (5 of 16 alleles) in Chinese PDE patients.

The pharmacogenomics of epilepsy

Genetic factors contribute to the high interindividual variability in response to antiepileptic drugs. However, most genetic markers identified to date have limited sensitivity and specificity, and the value of genetic testing in guiding antiepileptic drug (AED) therapy is limited. The best defined indication for testing relates to HLA-B*15:02 genotyping to identify those individuals of South Asian ethnicity who are at high risk for developing serious adverse cutaneous reactions to carbamazepine. The indication for HLA-A*31:01 testing to identify individuals at risk for skin reactions from carbamazepine, or for CYP2C9 genotyping to identify individuals at risk for serious skin reactions from phenytoin is less compelling. The use of genetic testing to guide epilepsy treatment is likely to increase in the future, as better understanding of the function of epilepsy genes will permit the application of precision medicine targeting the biological mechanisms responsible for epilepsy in the specific individual.

Triple therapy with pyridoxine, arginine supplementation and dietary lysine restriction in pyridoxine-dependent epilepsy: Neurodevelopmental outcome

Pyridoxine-dependent epilepsy (PDE) is an epileptic encephalopathy characterized by response to pharmacologic doses of pyridoxine. PDE is caused by deficiency of α-aminoadipic semialdehyde dehydrogenase resulting in impaired lysine degradation and subsequent accumulation of α-aminoadipic semialdehyde. Despite adequate seizure control with pyridoxine monotherapy, 75% of individuals with PDE have significant developmental delay and intellectual disability. We describe a new combined therapeutic approach to reduce putative toxic metabolites from impaired lysine metabolism. This approach utilizes pyridoxine, a lysine-restricted diet to limit the substrate that leads to neurotoxic metabolite accumulation and L-arginine to compete for brain lysine influx and liver mitochondrial import. We report the developmental and biochemical outcome of six subjects who were treated with this triple therapy. Triple therapy reduced CSF, plasma, and urine biomarkers associated with neurotoxicity in PDE. The addition of arginine supplementation to children already treated with dietary lysine restriction and pyridoxine further reduced toxic metabolites, and in some subjects appeared to improve neurodevelopmental outcome. Dietary lysine restriction was associated with improved seizure control in one subject, and the addition of arginine supplementation increased the objective motor outcome scale in two twin siblings, illustrating the contribution of each component of this treatment combination. Optimal results were noted in the individual treated with triple therapy early in the course of the disease. Residual disease symptoms could be related to early injury suggested by initial MR imaging prior to initiation of treatment or from severe epilepsy prior to diagnosis. This observational study reports the use of triple therapy, which combines three effective components in this rare condition, and suggests that early diagnosis and treatment with this new triple therapy may ameliorate the cognitive impairment in PDE.