Glial localization of antiquitin: implications for pyridoxine-dependent epilepsy

Genotype and phenotype features and prognostic factors of neonatal-onset pyridoxine-dependent epilepsy: A systematic review

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is a rare autosomal recessive disorder due to a deficiency of α-aminoadipic semialdehyde dehydrogenase. This study aimed to systematically explore genotypic and phenotypic features and prognostic factors of neonatal-onset PDE. A literature search covering PubMed, Elsevier, and Web of Science was conducted from January 2006 to August 2023. We identified 56 eligible studies involving 169 patients and 334 alleles. The c.1279 G>C variant was the most common variant of neonatal-onset PDE (25.7 %). All patients were treated with pyridoxine; forty patients received dietary intervention therapy. 63.9 % of the patients were completely seizure-free; however, 68.6 % of the patients had neurodevelopmental delays. Additionally, homozygous c.1279 G>C variants were significantly associated with ventriculomegaly, abnormal white matter signal, and cysts (P<0.05). In contrast, homozygous c.1364 T>C was associated with clonic seizure (P=0.031). Pyridoxine used immediately at seizure onset was an independent protective factor for developmental delay (P=0.035; odds ratio [OR]: 3.14). Besides, pyridoxine used early in the neonatal period was a protective factor for language delay (P=0.044; OR: 4.59). In contrast, neonatal respiratory distress (P=0.001; OR: 127.44) and abnormal brain magnetic resonance imaging (P=0.049; OR: 3.64) were risk factors. Prenatal movement abnormality (P=0.041; OR: 20.56) and abnormal white matter signal (P=0.012; OR: 24.30) were risk factors for motor delay. Myoclonic seizure (P=0.023; OR: 7.13) and status epilepticus (P=0.000; OR: 9.93) were risk factors for breakthrough seizures. In conclusion, our study indicated that pyridoxine should be started immediately when unexplained neonatal seizures occur and not later than the neonatal period to prevent poor neurodevelopmental outcomes.

Update current understanding of neurometabolic disorders related to lysine metabolism

Lysine, as an essential amino acid, predominantly undergoes metabolic processes through the saccharopine pathway, whereas a smaller fraction follows the pipecolic acid pathway. Although the liver is considered the primary organ for lysine metabolism, it is worth noting that lysine catabolism also takes place in other tissues and organs throughout the body, including the brain. Enzyme deficiency caused by pathogenic variants in its metabolic pathway may lead to a series of neurometabolic diseases, among which glutaric aciduria type 1 and pyridoxine-dependent epilepsy have the most significant clinical manifestations. At present, through research, we have a deeper understanding of the multiple pathophysiological mechanisms related to these diseases, including intracerebral accumulation of neurotoxic metabolites, imbalance between GABAergic and glutamatergic neurotransmission, energy deprivation due to metabolites, and the dysfunction of antiquitin. Because of the complexity of these diseases, their clinical manifestations are also diverse. The early implementation of lysine-restricted diets and supplementation with arginine and carnitine has reported positive impacts on the neurodevelopmental outcomes of patients. Presently, there is more robust evidence supporting the effectiveness of these treatments in glutaric aciduria type 1 compared with pyridoxine-dependent epilepsy.

Molecular analysis and prenatal diagnosis of seven Chinese families with genetic epilepsy

Introduction

Genetic epilepsy is a large group of clinically and genetically heterogeneous neurological disorders characterized by recurrent seizures, which have a clear association with genetic defects. In this study, we have recruited seven families from China with neurodevelopmental abnormalities in which epilepsy was a predominant manifestation, aiming to elucidate the underlying causes and make a precise diagnosis for the cases.

Methods

Whole-exome sequencing (WES) combined with Sanger sequencing was used to identify the causative variants associated with the diseases in addition to essential imaging and biomedical examination.

Results

A gross intragenic deletion detected in MFSD8 was investigated via gap-polymerase chain reaction (PCR), real-time quantitative PCR (qPCR), and mRNA sequence analysis. We identified 11 variants in seven genes (ALDH7A1, CDKL5, PCDH19, QARS1, POLG, GRIN2A, and MFSD8) responsible for genetic epilepsy in the seven families, respectively. A total of six variants (c.1408T>G in ALDH7A1, c.1994_1997del in CDKL5, c.794G>A in QARS1, c.2453C>T in GRIN2A, and c.217dup and c.863+995_998+1480del in MFSD8) have not yet been reported to be associated with diseases and were all evaluated to be pathogenic or likely pathogenic according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Methods

Based on the molecular findings, we have associated the intragenic deletion in MFSD8 with the mutagenesis mechanism of Alu-mediated genomic rearrangements for the first time and provided genetic counseling, medical suggestions, and prenatal diagnosis for the families. In conclusion, molecular diagnosis is crucial to obtain improved medical outcomes and recurrence risk evaluation for genetic epilepsy.

Global Metabolomics Discovers Two Novel Biomarkers in Pyridoxine-Dependent Epilepsy Caused by ALDH7A1 Deficiency

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive developmental and epileptic encephalopathy caused by pathogenic variants in the ALDH7A1 gene (PDE-ALDH7A1), which mainly has its onset in neonates and infants. Early diagnosis and treatment are crucial to prevent severe neurological sequelae or death. Sensitive, specific, and stable biomarkers for diagnostic evaluations and follow-up examinations are essential to optimize outcomes. However, most of the known biomarkers for PDE lack these criteria. Additionally, there is little discussion regarding the interdependence of biomarkers in the PDE-ALDH7A1 metabolite profile. Therefore, the aim of this study was to understand the underlying mechanisms in PDE-ALDH7A1 and to discover new biomarkers in the plasma of patients using global metabolomics. Plasma samples from 9 patients with genetically confirmed PDE-ALDH7A1 and 22 carefully selected control individuals were analyzed by ultra high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). Two novel and reliable pyridoxine-independent diagnostic markers, 6-hydroxy-2-aminocaproic acid (HACA) and an isomer of C₉H₁₁NO₄, were identified. Furthermore, a possible reaction mechanism is proposed for HACA. This study demonstrates the capability of global metabolomics in disease screening to detect established and novel biomarkers.

A novel mouse model for pyridoxine-dependent epilepsy due to antiquitin deficiency

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disease caused by mutations in the ALDH7A1 gene leading to blockade of the lysine catabolism pathway. PDE is characterized by recurrent seizures that are resistant to conventional anticonvulsant treatment but are well-controlled by pyridoxine (PN). Most PDE patients also suffer from neurodevelopmental deficits despite adequate seizure control with PN. To investigate potential pathophysiological mechanisms associated with ALDH7A1 deficiency, we generated a transgenic mouse strain with constitutive genetic ablation of Aldh7a1. We undertook extensive biochemical characterization of Aldh7a1-KO mice consuming a low lysine/high PN diet. Results showed that KO mice accumulated high concentrations of upstream lysine metabolites including ∆1-piperideine-6-carboxylic acid (P6C), α-aminoadipic semialdehyde (α-AASA) and pipecolic acid both in brain and liver tissues, similar to the biochemical picture in ALDH7A1-deficient patients. We also observed preliminary evidence of a widely deranged amino acid profile and increased levels of methionine sulfoxide, an oxidative stress biomarker, in the brains of KO mice, suggesting that increased oxidative stress may be a novel pathobiochemical mechanism in ALDH7A1 deficiency. KO mice lacked epileptic seizures when fed a low lysine/high PN diet. Switching mice to a high lysine/low PN diet led to vigorous seizures and a quick death in KO mice. Treatment with PN controlled seizures and improved survival of high-lysine/low PN fed KO mice. This study expands the spectrum of biochemical abnormalities that may be associated with ALDH7A1 deficiency and provides a proof-of-concept for the utility of the model to study PDE pathophysiology and to test new therapeutics.

Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy

BackgroundPyridoxine-dependent epilepsy (PDE-ALDH7A1) is an inborn error of lysine catabolism that presents with refractory epilepsy in newborns. Biallelic ALDH7A1 variants lead to deficiency of α-aminoadipic semialdehyde dehydrogenase/antiquitin, resulting in accumulation of piperideine-6-carboxylate (P6C), and secondary deficiency of the important cofactor pyridoxal-5'-phosphate (PLP, active vitamin B6) through its complexation with P6C. Vitamin B6 supplementation resolves epilepsy in patients, but intellectual disability may still develop. Early diagnosis and treatment, preferably based on newborn screening, could optimize long-term clinical outcome. However, no suitable PDE-ALDH7A1 newborn screening biomarkers are currently available.MethodsWe combined the innovative analytical methods untargeted metabolomics and infrared ion spectroscopy to discover and identify biomarkers in plasma that would allow for PDE-ALDH7A1 diagnosis in newborn screening.ResultsWe identified 2S,6S-/2S,6R-oxopropylpiperidine-2-carboxylic acid (2-OPP) as a PDE-ALDH7A1 biomarker, and confirmed 6-oxopiperidine-2-carboxylic acid (6-oxoPIP) as a biomarker. The suitability of 2-OPP as a potential PDE-ALDH7A1 newborn screening biomarker in dried bloodspots was shown. Additionally, we found that 2-OPP accumulates in brain tissue of patients and Aldh7a1-knockout mice, and induced epilepsy-like behavior in a zebrafish model system.ConclusionThis study has opened the way to newborn screening for PDE-ALDH7A1. We speculate that 2-OPP may contribute to ongoing neurotoxicity, also in treated PDE-ALDH7A1 patients. As 2-OPP formation appears to increase upon ketosis, we emphasize the importance of avoiding catabolism in PDE-ALDH7A1 patients.FundingSociety for Inborn Errors of Metabolism for Netherlands and Belgium (ESN), United for Metabolic Diseases (UMD), Stofwisselkracht, Radboud University, Canadian Institutes of Health Research, Dutch Research Council (NWO), and the European Research Council (ERC).

Cognitive and neurological outcome of patients in the Dutch pyridoxine-dependent epilepsy (PDE-ALDH7A1) cohort, a cross-sectional study

BACKGROUND

Pyridoxine monotherapy in PDE-ALDH7A1 often results in adequate seizure control, but neurodevelopmental outcome varies. Detailed long-term neurological outcome is unknown. Here we present the cognitive and neurological features of the Dutch PDE-ALDH7A1 cohort.

METHODS

Neurological outcome was assessed in 24 patients (age 1-26 years); classified as normal, complex minor neurological dysfunction (complex MND) or abnormal. Intelligence quotient (IQ) was derived from standardized IQ tests with five severity levels of intellectual disability (ID). MRI's and treatments were assessed.

RESULTS

Ten patients (42%) showed unremarkable neurological examination, 11 (46%) complex MND, and 3 (12%) cerebral palsy (CP). Minor coordination problems were identified in 17 (71%), fine motor disability in 11 (46%), posture/muscle tone deviancies in 11 (46%) and abnormal reflexes in 8 (33%). Six patients (25%) had an IQ > 85, 7 (29%) borderline, 7 (29%) mild, 3 (13%) moderate, and 1 severe ID. Cerebral ventriculomegaly on MRI was progressive in 11. Three patients showed normal neurologic exam, IQ, and MRI. Eleven patients were treated with pyridoxine only and 13 by additional lysine reduction therapy (LRT). LRT started at age <3 years demonstrated beneficial effect on IQ results in 3 patients.

DISCUSSION

Complex MND and CP occurred more frequently in PDE-ALDH7A1 (46% and 12%) than in general population (7% and 0.2%, Peters et al., 2011, Schaefer et al., 2008). Twenty-five percent had a normal IQ. Although LRT shows potential to improve outcomes, data are heterogeneous in small patient numbers. More research with longer follow-up via the International PDE Registry (www.pdeonline.org) is needed.

Simultaneous quantification of alpha-aminoadipic semialdehyde, piperideine-6-carboxylate, pipecolic acid and alpha-aminoadipic acid in pyridoxine-dependent epilepsy

The measurements of lysine metabolites provide valuable information for the rapid diagnosis of pyridoxine-dependent epilepsy (PDE). Here, we aimed to develop a sensitive method to simultaneously quantify multiple lysine metabolites in PDE, including α-aminoadipic semialdehyde (a-AASA), piperideine-6-carboxylate (P6C), pipecolic acid (PA) and α-aminoadipic acid (α-AAA) in plasma, serum, dried blood spots (DBS), urine and dried urine spots (DUS). Fifteen patients with molecularly confirmed PDE were detected using liquid chromatography-mass spectrometry (LC-MS/MS) method. Compared to the control groups, the concentrations of a-AASA, P6C and the sum of a-AASA and P6C (AASA-P6C) in all types of samples from PDE patients were markedly elevated. The PA and a-AAA concentrations ranges overlapped partially between PDE patients and control groups. The concentrations of all the analytes in plasma and serum, as well as in urine and DUS were highly correlated. Our study provided more options for the diverse sample collection in the biochemical tests according to practical requirements. With treatment modality of newly triple therapy investigated, biomarker study might play important role not only on diagnosis but also on treatment monitoring and fine tuning the diet. The persistently elevated analytes with good correlation between plasma and DBS, as well as urine and DUS made neonatal screening using DBS and DUS possible.

New insights into human lysine degradation pathways with relevance to pyridoxine-dependent epilepsy due to antiquitin deficiency

Deficiency of antiquitin (ATQ), an enzyme involved in lysine degradation, is the major cause of vitamin B₆ -dependent epilepsy. Accumulation of the potentially neurotoxic α-aminoadipic semialdehyde (AASA) may contribute to frequently associated developmental delay. AASA is formed by α-aminoadipic semialdehyde synthase (AASS) via the saccharopine pathway of lysine degradation, or, as has been postulated, by the pipecolic acid (PA) pathway, and then converted to α-aminoadipic acid by ATQ. The PA pathway has been considered to be the predominant pathway of lysine degradation in mammalian brain; however, this was refuted by recent studies in mouse. Consequently, inhibition of AASS was proposed as a potential new treatment option for ATQ deficiency. It is therefore of utmost importance to determine whether the saccharopine pathway is also predominant in human brain cells. The route of lysine degradation was analyzed by isotopic tracing studies in cultured human astrocytes, ReNcell CX human neuronal progenitor cells and human fibroblasts, and expression of enzymes of the two lysine degradation pathways was determined by Western blot. Lysine degradation was only detected through the saccharopine pathway in all cell types studied. The enrichment of ¹⁵ N-glutamate as a side product of AASA formation through AASS furthermore demonstrated activity of the saccharopine pathway. We provide first evidence that the saccharopine pathway is the major route of lysine degradation in cultured human brain cells. These results support inhibition of the saccharopine pathway as a new treatment option for ATQ deficiency.

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.

Malformations of Cerebral Cortex Development: Molecules and Mechanisms

Malformations of cortical development encompass heterogeneous groups of structural brain anomalies associated with complex neurodevelopmental disorders and diverse genetic and nongenetic etiologies. Recent progress in understanding the genetic basis of brain malformations has been driven by extraordinary advances in DNA sequencing technologies. For example, somatic mosaic mutations that activate mammalian target of rapamycin signaling in cortical progenitor cells during development are now recognized as the cause of hemimegalencephaly and some types of focal cortical dysplasia. In addition, research on brain development has begun to reveal the cellular and molecular bases of cortical gyrification and axon pathway formation, providing better understanding of disorders involving these processes. New neuroimaging techniques with improved resolution have enhanced our ability to characterize subtle malformations, such as those associated with intellectual disability and autism. In this review, we broadly discuss cortical malformations and focus on several for which genetic etiologies have elucidated pathogenesis.

The Effects of a Single Oral Dose of Pyridoxine on Alpha-Aminoadipic Semialdehyde, Piperideine-6-Carboxylate, Pipecolic Acid, and Alpha-Aminoadipic Acid Levels in Pyridoxine-Dependent Epilepsy

Purpose: To evaluate the effects of a single oral dose of pyridoxine on lysine metabolites including α-aminoadipic semialdehyde (a-AASA), piperideine-6-carboxylate (P6C), the sum of AASA and P6C (AASA-P6C), pipecolic acid (PA), and α-aminoadipic acid (α-AAA) in PDE patients. Methods: The lysine metabolites of 15 patients with molecularly confirmed PDE were detected before and 4 h after taking a single oral dose of pyridoxine, respectively, using liquid chromatography-mass spectrometry (LC-MS/MS) method. Five types of samples were freshly prepared, including plasma, serum, dried blood spots (DBS), urine, and dried urine spots (DUS). Results: All the patients had been treated with long-term oral pyridoxine for several months to years, with doses of 30-360 mg/d. The concentrations of a-AASA, P6C, AASA-P6C, PA, and a-AAA before and after taking a single oral dose of pyridoxine for the same analyte detected in the same type of sample varied among patients. The mean concentrations increased in almost all the metabolites after taking an oral dose of pyridoxine, with or without statistical significance. Whereas, the metabolites concentrations might increase or decrease among different patients, or in different samples of the same patient, without a regular tendency. There was no statistical correlation between the concentrations before and after taking pyridoxine in the same type of sample for most metabolites. Conclusions: No obvious relationship between the metabolite levels or concentration differences and the age, pyridoxine dose (a single oral dose and long-term maintenance dose), duration of treatment, or neurodevelopmental phenotype was found at present study. The large individual differences among patients, probably affected by various genotypes, leading to quite different effects of pyridoxine on the change degree of metabolites concentrations. Our study suggested that long-term pyridoxine treatment could control seizures rather than getting toxic lysine metabolites such as a-AASA and P6C back to normal. In the future, more therapies should be focused to alleviate the metabolites accumulation and further improve the prognosis of PDE.

Brain malformations associated to Aldh7a1 gene mutations: Report of a novel homozygous mutation and literature review

BACKGROUND

The ALDH7A1 gene is known to be responsible for autosomal recessive pyridoxine-dependent epilepsy (OMIM 266100). The phenotypic spectrum of ALDH7A1 mutations is very heterogeneous ranging from refractory epilepsy and neurodevelopmental delay, to multisystem neonatal disorder.

AIM

The present study aims at describing the phenotype associated with a novel homozygous ALDH7A1 mutation and the spectrum of brain malformations associated with pyridoxine-dependent epilepsy.

METHODS

We conducted a literature review on the Internet database Pubmed (up to November 2017) searching for ALDH7A1 mutations associated with brain malformations and brain MRI findings.

RESULTS

We present the case of two siblings, children of related parents. The proband presented neonatal focal seizures not responding to conventional antiepileptic drugs. Electroencephalography showed a suppression burst pattern and several multifocal ictal patterns, responsive to pyridoxine. Brain MRI was normal. Molecular analysis by targeted next-generation sequencing panel for epileptic encephalopathy disclosed a homozygous missense mutation of ALDH7A1. The same mutation was then found in a stored sample of DNA from peripheral blood of an older sister dead 3 years earlier. This girl presented a complex brain malformation diagnosed with a foetal MRI and had neonatal refractory seizures with suppression burst pattern. She died at 6 months of age.

LITERATURE REVIEW

The brain abnormalities most frequently reported in pyridoxine-dependent epilepsy include: agenesia/hypoplasia of the corpus callosum, not specific white matter abnormalities, large cisterna magna, ventriculomegaly, haemorrhages, cerebellum hypoplasia/dysplasia, and, more rarely, dysplasia of the brainstem and hydrocephalus.

DISCUSSION AND CONCLUSIONS

ALDH7A1 mutations have been associated to different brain abnormalities, documented by MRI only in few cases. The study cases expand the clinical spectrum of ALDH7A1 associated conditions, suggesting to look for ALDH7A1 mutations not only in classical phenotypes but also in patients with brain malformations, mainly if there is a response to a pyridoxine trial.

Neurometabolic Disorders of the Newborn

There is an extensive and diverse set of medical conditions affecting the neonatal brain within the spectrum of neurometabolic disorders. As such, their clinical presentations can be rather nonspecific, and can often mimic acquired entities such as hypoxic-ischemic encephalopathy and sepsis. Similarly, the radiological findings in these entities can also be frequently nonspecific, but a more detailed analysis of imaging findings (especially magnetic resonance imaging) alongside the relevant clinical details can be a rewarding experience, thus enabling a timely and targeted diagnosis. Early diagnosis of an underlying neurometabolic disorder is vital, as some of these entities are potentially treatable, and laboratory and genetic testing can be precisely targeted. Further, their detection helps with counselling families for future pregnancies. We present a review of neurometabolic disorders specific to the newborns with a focus on how neuroimaging findings match their clinical presentation patterns.

Geometric morphometrics reveal altered corpus callosum shape in pyridoxine-dependent epilepsy

OBJECTIVE

To evaluate the features and maturational changes in overall callosal shape in patients with pyridoxine-dependent epilepsy (PDE).

METHODS

Measurements were conducted through landmark-based geometric morphometrics applied on cerebral MRIs of patients with PDE and age-matched control subjects. The outline of the corpus callosum was manually traced in the midsagittal plane. Three hundred semi-landmarks along the outline were collected and underwent statistical generalized Procrustes analysis. An allometric regression was applied to evaluate the callosal shape due to growth over time.

RESULTS

Thirty-eight patients with PDE and 38 age- and sex-matched control subjects were included. Mean age at the time of the MRI in the patient group was 9.3 years (median 6.3 years, range 0.01-48 years). Significant differences (p < 0.01) in the mean callosal shape between patients and controls were found. The allometric regression model revealed significant shape variations (p < 0.01) between the 2 study groups across the developmental course after controlling for the effect of callosal size on shape. This latter effect turned out to be significant as well (p < 0.001).

CONCLUSIONS

Patients with PDE show an altered callosal shape and variations in callosal ontogeny, which are likely secondary to the underlying genetic defect with abnormal function of antiquitin, the product of the ALDH7A1 gene.

Hydrocephalus in pyridoxine-dependent epilepsy: New case and literature review

INTRODUCTION

Pyridoxine-dependent epilepsy (PDE) is a rare disorder of the lysine metabolism, characterized by a pharmacoresistant epileptic encephalopathy that usually begins in the neonatal period. However, its phenotypic spectrum is wide and not limited to seizures. We report a new case of PDE who developed hydrocephalus, along with an exhaustive review of the literature.

CASE REPORT

Our patient presented with seizures at 13 h of life. Antiepileptic drugs, vitamins and cofactors were required to achieve seizure control. Laboratory tests were congruent with PDE. She remained seizure-free until age five months, when seizures reappeared in the context of increasing head size and irritability. A cranial ultrasound showed hydrocephalus, for which she underwent ventriculoperitoneal shunting.

DISCUSSION

Seven other patients with same features have been previously reported. Seizure onset occurred within the first 7 days in all patients. Most of the children developed hydrocephalus at 6-7 months of age. In 4 out of 7 a genetic mutation was identified, despite the accurate etiology of hydrocephalus was unknown in most of them. The case we report behaved similarly to the others previously described. We postulate that the pathogenesis of this complication could be related to the high expression of antiquitin in choroid plexus epithelium, where the cerebrospinal fluid is produced.

CONCLUSIONS

patients with PDE should be closely monitored, since they may present severe complications. We highlight the development of hydrocephalus, an uncommon but potentially life-threatening problem reported in 8 patients up to present time.

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.

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.

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.

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.

Corpus Callosum Diffusion and Connectivity Features in High Functioning Subjects With Pyridoxine-Dependent Epilepsy

BACKGROUND

In this observational study, white matter structure, functional magnetic resonance imaging (fMRI) task-based responses, and functional connectivity were assessed in four subjects with high functioning pyridoxine-dependent epilepsy and age-matched control subjects.

METHODS

Four male subjects with pyridoxine-dependent epilepsy (mean age 31 years 8 months, standard deviation 12 years 3 months) and age-matched control subjects (32 years 4 months, standard deviation 13 years) were recruited to participate in the study. Diffusion tensor data were collected and postprocessed in Functional Magnetic Resonance Imaging of the Brain Software Library to quantify corpus callosum tracts as a means to assess white matter structure. Task-based fMRI data were collected and Functional Magnetic Resonance Imaging of the Brain Software Library used to assess task response. The fMRI resting-state data were analyzed with the functional connectivity toolbox Conn to determine functional connectivity.

RESULTS

Subjects with high functioning pyridoxine-dependent epilepsy retained structural white matter connectivity compared with control subjects, despite morphologic differences in the posterior corpus callosum. fMRI task-based results did not differ between subjects with pyridoxine-dependent epilepsy and control subjects; functional connectivity as measured with resting-state fMRI was lower in subjects with pyridoxine-dependent epilepsy for several systems (memory, somatosensory, auditory).

CONCLUSION

Although corpus callosum morphology is diminished in the posterior portions, structural connectivity was retained in subjects with pyridoxine-dependent epilepsy, while functional connectivity was diminished for memory, somatosensory, and auditory systems.

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.

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.

Callosal alterations in pyridoxine-dependent epilepsy

AIM

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.

METHOD

Spanning a wide age range from birth to 48 years, 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).

RESULTS

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.

INTERPRETATION

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.

Lysine-Restricted Diet as Adjunct Therapy for Pyridoxine-Dependent Epilepsy: The PDE Consortium Consensus Recommendations

BACKGROUND

Seventy-five percent of patients with pyridoxine-dependent epilepsy (PDE) due to Antiquitin (ATQ) deficiency suffer from developmental delay and/or intellectual disability (IQ < 70) despite seizure control. An observational study showed that adjunct treatment with a lysine-restricted diet is safe, results in partial normalization of lysine intermediates in body fluids, and may have beneficial effects on seizure control and psychomotor development.

METHODS

In analogy to the NICE guideline process, the international PDE Consortium, an open platform uniting scientists and clinicians working in the field of this metabolic epilepsy, during four workshops (2010-2013) developed a recommendation for a lysine-restricted diet in PDE, with the aim of standardizing its implementation and monitoring of patients. Additionally, a proposal for a further observational study is suggested.

RESULTS

(1) All patients with confirmed ATQ deficiency are eligible for adjunct treatment with lysine-restricted diet, unless treatment with pyridoxine alone has resulted in complete symptom resolution, including normal behavior and development. (2) Lysine restriction should be started as early as possible; the optimal duration remains undetermined. (3) The diet should be implemented and the patient be monitored according to these recommendations in order to assure best possible quality of care and safety.

DISCUSSION

The implementation of this recommendation will provide a unique and a much needed opportunity to gather data with which to refine the recommendation as well as improve our understanding of outcomes of individuals affected by this rare disease. We therefore propose an international observational study that would utilize freely accessible, online data sharing technologies to generate more evidence.