Pyridoxine-dependent Epilepsy Research Articles

Structural Basis of Substrate Recognition by Aldehyde Dehydrogenase 7A1.

Aldehyde dehydrogenase 7A1 (ALDH7A1) is part of lysine catabolism and catalyzes the NAD+-dependent oxidation of α-aminoadipate semialdehyde to α-aminoadipate. Herein, we describe a structural study of human ALDH7A1 focused on substrate recognition. Five crystal structures and small-angle X-ray scattering data are reported, including the first crystal structure of any ALDH7 family member complexed with α-aminoadipate. The product binds with the ε-carboxylate in the oxyanion hole, the aliphatic chain packed into an aromatic box, and the distal end of the product anchored by electrostatic interactions with five conserved residues. This binding mode resembles that of glutamate bound to the proline catabolic enzyme ALDH4A1. Analysis of ALDH7A1 and ALDH4A1 structures suggests key interactions that underlie substrate discrimination. Structures of apo ALDH7A1 reveal dramatic conformational differences from the product complex. Product binding is associated with a 16 Å movement of the C-terminus into the active site, which stabilizes the active conformation of the aldehyde substrate anchor loop. The fact that the C-terminus is part of the active site was hitherto unknown. Interestingly, the C-terminus and aldehyde anchor loop are disordered in a new tetragonal crystal form of the apoenzyme, implying that these parts of the enzyme are highly flexible. Our results suggest that the active site of ALDH7A1 is disassembled when the aldehyde site is vacant, and the C-terminus is a mobile element that forms quaternary structural interactions that aid aldehyde binding. These results are relevant to the c.1512delG genetic deletion associated with pyridoxine-dependent epilepsy, which alters the C-terminus of ALDH7A1.

First cases of pyridoxine-dependent epilepsy in Bulgaria: novel mutation in the ALDH7A1 gene.

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder characterized by intractable seizures in neonates and infants. The seizures cannot be controlled with antiepileptic medications but respond both clinically and electrographically to large daily supplements of pyridoxine (vitamin B6). PDE is caused by mutations in the ALDH7A1 gene. Molecular genetic analysis of the ALDH7A1 gene was performed in seven patients, referred with clinical diagnosis of PDE. Mutations were detected in a dizygotic twin pair and a non-related boy with classical form of PDE. Direct sequencing of the ALDH7A1 gene revealed one novel (c.297delG, p.Trp99*) and two already reported (c.328C>T, p.Arg110*; c.584A>G, p.Asn195Ser) mutations. Here, we report the first genetically proven cases of PDE in Bulgaria.

Intragenic deletions of ALDH7A1 in pyridoxine-dependent epilepsy caused by Alu-Alu recombination.

To investigate the role of intragenic deletions of ALDH7A1 in patients with clinical and biochemical evidence of pyridoxine-dependent epilepsy but only a single identifiable mutation in ALDH7A1. We designed a custom oligonucleotide array with high-density probe coverage across the ALDH7A1 gene. We performed array comparative genomic hybridization in 6 patients with clinical and biochemical evidence of pyridoxine-dependent epilepsy but only a single detectable mutation in ALDH7A1 by sequence analysis. We found partial deletions of ALDH7A1 in 5 of 6 patients. Breakpoint analysis reveals that the deletions are likely a result of Alu-Alu recombination in all cases. The density of Alu elements within introns of ALDH7A1 suggests susceptibility to recurrent rearrangement. Patients with clinical pyridoxine-dependent epilepsy and a single identifiable mutation in ALDH7A1 warrant further investigation for copy number changes involving the ALHD7A1 gene.

Pyridoxine dependent epilepsy: Seizure onset, seizure types and EEG features

Pyridoxine dependent epilepsy (PDE) is an autosomal recessively inherited disorder. It is caused by mutations in the ALDH7A1 gene (PDE-ALDH7A1) encoding the alpha-aminoadipic semialdehyde dehydrogenase enzyme in the lysine catabolic pathway. The alpha-aminoadipic semialdehyde dehydrogenase enzyme deficiency leads to accumulation of alpha-aminoadipic semialdehyde and piperidine 6-carboxylic acid, the latter inactivates pyridoxal-5-phosphate. The majority of the patients present with neonatal onset intractable seizures with a dramatic response to pyridoxine therapy. Later seizure onset up to 3 yr of age has been reported too. Generalized tonic-clonic seizures are the most common seizure type. The treatment of PDE consists of high dose pyridoxine supplementation therapy. Since the underlying genetic defect was identified in the lysine catabolic pathway, few patients were treated with lysine-restricted diet to decrease, likely neurotoxic, alpha-aminoadipic semialdehyde and piperidine 6-carboxylic acid accumulation in the central nervous system.

2015 update on triple therapy for pyridoxine-dependent epilepsy

Background & Objectives: Of patients with pyridoxine-dependent epilepsy (PDE) due to ATQ deficiency, 75% suffer intellectual disability despite adequate seizure control with high dose pyridoxine. We aimed to assess the safety and efficacy of two novel therapeutic strategies to reduce accumulation of toxic intermediates in this cerebral lysine degradation defect. Methods: In two open-label observational studies, seven children with confirmed ATQ deficiency were started on dietary lysine restriction with regular nutritional monitoring, and outcome evaluation pipecolic acid, AASA levels in body fluids; development/cognition via age-appropriate tests and parental observations; epilepsy). Subsequently additional arginine supplementation was initiated to reduce cerebral lysine flux (cation transporter competitive inhibition).. Results: Lysine-restriction was well tolerated and diet is safe, resulted in reduction of lysine intermediates in all body fluids in all patients (up to 80% reduction AASA in cerebrospinal fluid), with beneficial effects on seizure control and psychomotor development. Additional arginine fortification resulted in normalization of biomarkers and dramatic improvement of psychomotor development. Discussion: Triple therapy is effective, especially if implemented early; studies for PDE newborn screening have been initiated. For dissemination and evidence generation, our PDE Consortium published Recommendations, developed a Digital Diet App and established a RedCap study database (www.pdeonline.org).

G66(P) Interesting cases of pyridoxine dependent epilepsy in late childhood

We report cases of two children with intractable epilepsy who responded to treatment with pyridoxine in late childhood. Case details Case 1: A 14 year old girl born following an uneventful pregnancy to non consanguinous parents. She has global developmental delay. She developed epilepsy at around 2 years of age. Her extensive investigations including an MRI of brain were normal. She had various types of seizures and these were refractory to antiepileptic medications. A trial of pyridoxine at around 13 years of age surprisingly had a very good effect on her seizure control. We are currently awaiting the result of urinary L-α-aminoadipic semialdehyde (AASA). Case 2: A 4 year old girl born following normal pregnancy developed infantile spasms at 4 months of age. She was treated with numerous courses of steroids with suboptimal response. Extended investigations including the MRI brain were normal. She eventually developed refractory epilepsy with cognitive decline. A trial of pyridoxine at 3 years of age achieved good control of epilepsy and improved her cognition as well. The urinary AASA was negative and the result of PNPO gene mutation is awaited. Discussion Pyridoxine dependent epilepsy is a syndrome that usually presents with neonatal intractable seizures. It may present later in infancy or early childhood. A variety of seizure types are reported, the most common being generalised tonic clonic seizures which progress to status epilepticus. Urinary AASA is usually elevated and the genetic testing is available for this condition now. Our cases responded to the empirical trial of Pyridoxine at a much later age. Conclusion We recommend testing for pyridoxine deficiency and therapeutic trial with pyridoxine in children with refractory epilepsy in all the age groups. Early detection and treatment of this condition not only achieves good seizure control but can possibly improve developmental outcome as well.

Diagnostic yield of genetic testing in epileptic encephalopathy in childhood.

Epilepsy is a common neurologic disorder of childhood. To determine the genetic diagnostic yield in epileptic encephalopathy, we performed a retrospective cohort study in a single epilepsy genetics clinic. We included all patients with intractable epilepsy, global developmental delay, and cognitive dysfunction seen between January 2012 and June 2014 in the Epilepsy Genetics Clinic. Electronic patient charts were reviewed for clinical features, neuroimaging, biochemical investigations, and molecular genetic investigations including targeted next-generation sequencing of epileptic encephalopathy genes. Genetic causes were identified in 28% of the 110 patients: 7% had inherited metabolic disorders including pyridoxine dependent epilepsy caused by ALDH7A1 mutation, Menkes disease, pyridox(am)ine-5-phosphate oxidase deficiency, cobalamin G deficiency, methylenetetrahydrofolate reductase deficiency, glucose transporter 1 deficiency, glycine encephalopathy, and pyruvate dehydrogenase complex deficiency; 21% had other genetic causes including genetic syndromes, pathogenic copy number variants on array comparative genomic hybridization, and epileptic encephalopathy related to mutations in the SCN1A, SCN2A, SCN8A, KCNQ2, STXBP1, PCDH19, and SLC9A6 genes. Forty-five percent of patients obtained a genetic diagnosis by targeted next-generation sequencing epileptic encephalopathy panels. It is notable that 4.5% of patients had a treatable inherited metabolic disease. To the best of our knowledge, this is the first study to combine inherited metabolic disorders and other genetic causes of epileptic encephalopathy. Targeted next-generation sequencing panels increased the genetic diagnostic yield from <10% to >25% in patients with epileptic encephalopathy.

Current treatment and management of pyridoxine-dependent epilepsy.

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder and is considered as a prototypical form of metabolic epilepsy. Characterized by recurrent seizures in the prenatal, neonatal, and/or postnatal periods that are resistant to conventional anti-epileptic drugs, PDE is responsive to pharmacological dosages of pyridoxine. Presently, however, there are no clear dose recommendations for long-term treatment. While pyridoxine supplementation is the first line of treatment and should be initiated in all confirmed PDE patients at an early age, various other treatment strategies are emerging. These include a lysine-restricted diet and arginine fortification. These will be discussed in light of current evidence, together with recommendations for best management of patients with this rare but treatable metabolic epilepsy, and future research and collaborative efforts, including the International PDE Consortium.

Single amino acid polymorphism in aldehyde dehydrogenase gene superfamily.

The aldehyde dehydrogenase gene superfamily comprises of 19 genes and 3 pseudogenes. These superfamily genes play a vital role in the formation of molecules that are involved in life processes, and detoxification of endogenous and exogenous aldehydes. ALDH superfamily genes associated mutations are implicated in various diseases, such as pyridoxine-dependent seizures, gamma-hydroxybutyric aciduria, type II Hyperprolinemia, Sjogren-Larsson syndrome including cancer and Alzheimer's disease. Accumulation of large DNA variations data especially Single Amino acid Polymorphisms (SAPs) in public databases related to ALDH superfamily genes insisted us to conduct a survey on the disease associated mutations and predict their function impact on protein structure and function. Overall this study provides an update and highlights the importance of pathogenic mutations in associated diseases. Using KD4v and Project HOPE a computational based platform, we summarized all the deleterious properties of SAPs in ALDH superfamily genes by the providing valuable insight into structural alteration rendered due to mutation. We hope this review might provide a way to define the deleteriousness of a SAP and helps to understand the molecular basis of the associated disease and also permits precise diagnosis and treatment in the near future.

Prevalence of inherited neurotransmitter disorders in patients with movement disorders and epilepsy: a retrospective cohort study.

BackgroundInherited neurotransmitter disorders are primary defects of neurotransmitter metabolism. The main purpose of this retrospective cohort study was to identify prevalence of inherited neurotransmitter disorders.MethodsThis retrospective cohort study does not have inclusion criteria; rather included all patients who underwent cerebrospinal fluid (CSF) homovanillic and 5-hydroxyindol acetic acid measurements. Patients with CSF neurotransmitter investigations suggestive of an inherited neurotransmitter disorder and patients with normal or non-diagnostic CSF neurotransmitter investigations underwent direct sequencing of single gene disorders.ResultsThere were 154 patients between October 2004 and July 2013. Four patients were excluded due to their diagnosis prior to this study dates. Two major clinical feature categories of patients who underwent lumbar puncture were movement disorders or epilepsy in our institution. Twenty out of the 150 patients (13.3%) were diagnosed with a genetic disorder including inherited neurotransmitter disorders (6 patients) (dihydropteridine reductase, 6-pyruvoyl-tetrahydropterin synthase, guanosine triphosphate cyclohydrolase I, tyrosine hydroxylase, pyridoxine dependent epilepsy due to mutations in the ALDH7A1 gene and pyridoxamine-5-phosphate oxidase deficiencies) and non-neurotransmitter disorders (14 patients).ConclusionPrevalence of inherited neurotransmitter disorders was 4% in our retrospective cohort study. Eight out of the 150 patients (5.3%) had one of the treatable inherited metabolic disorders with favorable short-term neurodevelopmental outcomes, highlighting the importance of an early and specific diagnosis. Whole exome or genome sequencing might shed light to unravel underlying genetic defects of new inherited neurotransmitter disorders in near future.

Determination of plasma pipecolic acid by an easy and rapid liquid chromatography–tandem mass spectrometry method

Pipecolic acid (PA) is an important biochemical marker for the diagnosis of peroxisomal disorders. PA is also a factor responsible for hepatic encephalopathy and a possible biomarker for pyridoxine-dependent seizures. We developed an easy and rapid PA quantification method, by high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS), requiring no derivatization and applicable to small sample volumes.Plasma (100μl) is extracted with 500μl acetonitrile (ACN) containing 2μmol/l [2H5]-phenylalanine as internal standard, vortexed and centrifuged. The supernatant is analyzed by HPLC-MS/MS in positive-ion mode using multiple reaction monitoring scan type. HPLC column is a Luna HILIC (150×3.0mm; 3μ 200A): Buffer A: ammonium formate 5mmol/l; Buffer B: ACN/H20 90:10 containing ammonium formate 5mmol/l. PA retention time is 4.86min.Recovery was 93.8%, linearity was assessed between 0.05 and 50μmol/l (R2=0.998), lower limit of detection was 0.010μmol/l and lower limit of quantification was 0.050μmol/l. Coefficient of variation was 3.2% intra-assay and 3.4% inter-assay, respectively.Clinical validation was obtained by comparing PA plasma values from 5 patients affected by peroxisomal disorders (mean, 23.38μmol/l; range, 11.20–37.1μmol/l) to 24 ages related healthy subjects (mean, 1.711μmol/l; range, 0.517–3.580μmol/l).

Early identification of treatable inborn errors of metabolism in children with intellectual disability: The Treatable Intellectual Disability Endeavor protocol in British Columbia.

Intellectual disability (ID) is a lifelong, debilitating condition affecting 2% to 3% Canadians (1). It is defined by deficits in cognitive functioning (IQ 2 developmental domains, eg, fine/gross motor skills, speech and interaction) (2,3). In Canada, approximately 7600 to 11,500 children are born with GDD annually (1). In the present commentary, the term ID will be used to refer to ID/GDD.

Novel therapy for pyridoxine dependent epilepsy due to ALDH7A1 genetic defect: l-arginine supplementation alternative to lysine-restricted diet

Background and hypothesisPyridoxine dependent epilepsy (PDE) due to mutations in the ALDH7A1 gene (PDE-ALDH7A1) is caused by α-aminoadipic-semialdehyde-dehydrogenase enzyme deficiency in the lysine pathway resulting in the accumulation of α-aminoadipic acid semialdehyde (α-AASA). Classical presentation is neonatal intractable seizures with a dramatic response to pyridoxine. Pyridoxine therapy does not prevent developmental delays in the majority of the patients. We hypothesized that l-arginine supplementation will decrease accumulation of α-AASA by competitive inhibition of lysine transport into the central nervous system and improve neurodevelopmental and neurocognitive functions in PDE-ALDH7A1. MethodsA 12-year-old male with PDE-ALDH7A1 was treated with l-arginine supplementation as an innovative therapy. Treatment outcome was monitored by cerebral-spinal-fluid (CSF) α-AASA measurements at baseline, 6th and 12th months of therapy. Neuropsychological assessments were performed at baseline and 12th months of therapy. Resultsl-arginine therapy was well tolerated without side effects. CSF α-AASA was decreased 57% at 12th months of therapy. Neuropsychological assessments revealed improvements in general abilities index from 108 to 116 and improvements in verbal and motor functioning at 12th months of therapy. ConclusionThe short-term treatment outcome of this novel l-arginine supplementation therapy for PDE-ALDH7A1 was successful for biochemical and neurocognitive improvements.

Corpus callosum alterations in pyridoxine-dependent epilepsy: a mirror image of an ongoing disease?

This commentary is on the original article by Friedman et al. on pages 1106–1110 of this issue.

Callosal alterations in pyridoxine-dependent epilepsy.

While there have been isolated reports of callosal morphology differences in pyridoxine-dependent epilepsy (PDE), a rare autosomal disorder caused by ALDH7A1 gene mutations, no study has systematically evaluated callosal features in a large sample of patients. This study sought to overcome this knowledge gap. Spanning a wide age range from birth to 48years, corpus callosum morphology and cross-sectional cerebral area were measured in 30 individuals with PDE (12 males, 18 females, median age 3.92y; 25th centile 0.27, 75th centile 15.25) compared to 30 age-matched comparison individuals (11 males, 19 females, median age 3.85y; 25th centile 0.26, 75th centile 16.00). Individuals with PDE were also divided into age groups to evaluate findings across development. As delay to treatment may modulate clinical severity, groups were stratified by treatment delay (less than or greater than 2wks from birth). Markedly reduced callosal area expressed as a ratio of mid-sagittal cerebral area was observed for the entire group with PDE (p<0.001). Stratifying by age (<1y, 1-10y, >10y) demonstrated posterior abnormalities to be a consistent feature, with anterior regions increasingly involved across the developmental trajectory. Splitting the PDE group by treatment lag did not reveal overall or sub-region callosal differences. Callosal abnormalities are a common feature of PDE not explained by treatment lag. Future work utilizing tract-based approaches to understand inter- and intra-hemispheric connectivity patterns will help in the better understanding the structural aspects of this disease.

Long-term treatment outcome of two patients with pyridoxine-dependent epilepsy caused by ALDH7A1 mutations: normal neurocognitive outcome.

Pyridoxine-dependent epilepsy is an autosomal recessively inherited disorder of lysine catabolism caused by mutations in the ALDH7A1 gene. We report 2 patients with normal neurocognitive outcome (full-scale IQ of 108 and 74) and their more than 10 years' treatment outcome on pyridoxine monotherapy. Both patients had specific borderline impairments in visual processing speed. More long-term treatment outcome reports will increase our knowledge about the natural history of the disease.

Fetal Onset Ventriculomegaly and Subependymal Cysts in a Pyridoxine Dependent Epilepsy Patient

Pyridoxine dependent epilepsy (PDE) is caused by mutations in the ALDH7A1 gene encoding α-aminoadipic semialdehyde dehydrogenase. The classic clinical presentation is neonatal seizures responsive only to pyridoxine therapy. White matter abnormalities, corpus callosum agenesis or hypoplasia, megacisterna magna, cortical dysplasia, neuronal heterotopias, intracerebral hemorrhage, and hydrocephalus in neuroimaging have been reported in patients with PDE. We report a new patient with asymmetric progressive ventriculomegaly noted on fetal sonography at 22 weeks' gestation. Postnatal brain sonography on day 1 and MRI on day 5 confirmed bilateral asymmetric ventriculomegaly caused by bilateral subependymal cysts. Intractable seizures at age 7 days initially responded to phenobarbital. Markedly elevated urinary α-aminoadipic acid semialdehyde levels and compound heterozygous mutations in the ALDH7A1 gene (c.446C>A/c.919C>T) confirmed the diagnosis of PDE caused by ALDH7A1 genetic defect. Despite the presence of structural brain malformations and subependymal cysts, PDE should always be included in the differential diagnosis of neonatal seizures that are refractory to treatment with antiepileptic drugs.

Clinical Diagnosis, Treatment, and ALDH7A1 Mutations in Pyridoxine-Dependent Epilepsy in Three Chinese Infants

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder that causes seizures in neonates and infants. Mutations of the ALDH7A1 gene are now recognized as the molecular basis PDE and help to define this disease. Three Chinese children with PDE were clinically analyzed, followed by treatment and examination of the ALDH7A1 mutations. The seizures of the 3 patients were all resistant to multiple anticonvulsants (2 to 7 types). For case 1, onset of seizures was at the age of 2 months. His seizures were well controlled by intravenous pyridoxine for several days at the age of 3 months 20 days and recurred at intervals of 13, 14 and 38 days after pyridoxine withdrawn for 3 times. At the age of 7 months, symptoms of PDE appeared and uninterrupted oral pyridoxine started. For case 2, her seizures occurred at 8 days after birth. After administration of multiple antiepileptic drugs observed ineffective, high-dose pyridoxine continuous therapy was taken at the age of 10 months and the significant treatment effect induced a diagnostic PDE. Seizure onset in case 3 was at the first day of birth. He experienced inadvertently pyridoxine therapy several times (first time at 2 days after birth) and achieved good therapeutic effect, which was confirmed by physicians until 4 months 10 days. The treatment process in our 3 patients suggested that pyridoxine should be early and purposefully used in patients with early onset seizures. ALDH7A1 gene mutation analysis revealed compound heterozygous mutations in each case: heterozygous c.410G>A (p.G137E) and IVS11+1G>A in case 1, heterozygous c.952G>C (p.A318P) and heterozygous c.965C>T (p.A322V) in case 2, and heterozygous c.902A>T (p.N301I) and IVS11+1G>A in case 3. Only p.N301I was reported previously, all other mutations were novel. This is the first time to report cases of Chinese patients diagnosed with PDE by molecular genetic analysis.

Pyridoxine or pyridoxal-5′-phosphate for neonatal epilepsy

The discovery of the cause of pyridoxine-dependent epilepsy (PDE), a unique autosomal recessive and treatable cause of refractory neonatal seizures, came 50 years after its first description with the identification of ALDH7A1 mutations leading to deficiency of the enzyme α-aminoadipic semialdehyde dehydrogenase (antiquitin).1 Dysfunction of this enzyme interferes with lysine degradation and leads to accumulation of a carboxylate product that irreversibly inactivates pyridoxal-5′-phosphate (PLP), the biologically active form of vitamin B6.

Overexpression of recombinant human antiquitin in E. coli: Partial enzyme activity in selected ALDH7A1 missense mutations associated with pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy (PDE) is an autosomal recessive disorder characterized by early onset seizures responsive to pyridoxine and caused by a defect in the α-aminoadipic semialdehyde dehydrogenase (antiquitin) gene (ALDH7A1). We selected four PDE-associated missense ALDH7A1 mutations, p.V367F, p.F410L, p.Q425R, and p.C450S, generated them in a recombinant human antiquitin cDNA with expression in E. coli at either 30°C or 37°C. One mutation, p.C450S, demonstrated substantial activity after expression at both temperatures, potentially contributing to milder biochemical and clinical phenotypes. The p.Q425R mutation yielded no activity at either temperature. The other two mutations yielded significant enzymatic activity at 30°C and markedly reduced activity at 37°C. For these latter three mutations, the markedly reduced or absent enzymatic activity resulting from expression at 37°C may be consistent with pathogenicity.