Pyridoxine-dependent seizures: demographic, clinical, MRI and psychometric features, and effect of dose on intelligence quotient

Clinical and biochemical outcome of a patient with pyridoxine-dependent epilepsy treated by triple therapy (pyridoxine supplementation, lysine-restricted diet, and arginine supplementation)

Pyridoxine-dependent epilepsy (PDE) is a recessive genetic disease characterized by epileptic encephalopathy with therapeutic response to pharmacological doses of pyridoxine and resistance to anti-epileptic treatments. The recent discovery in 2006 of the genetic defect antiquitin (ALDH7A1, OMIM #266100) has helped to understand the underlying mechanism, which is the accumulation of neurotoxic intermediates in the lysine catabolic pathway. The goal of the new therapeutic approach, termed triple therapy (TT) (pyridoxine, lysine-restricted diet and arginine supplementation), is to improve epilepsy control and neurocognitive development in patients with PDE. We present the 3-year treatment outcome for a child with PDE on pyridoxine treatment (started at age 5 months), lysine-restricted diet (started at age 17 months) and arginine supplementation therapy (started at age 19 months). The TT was well-tolerated with good compliance. No adverse events were reported. We observed a neurodevelopmental improvement, significantly fewer seizures, and a reduction of pipecolic acid (PA) as a biomarker of the illness. Our results show an improving clinical evolution, supporting and extending previous studies reporting efficacy of TT.

Inborn Errors of Metabolism in Pediatric Epilepsy

Patients with refractory epilepsy from inborn errors of metabolism typically present as neonates. Direct supplementation with the deficient vitamin or cofactor is recommended, and case series report both efficacy and safety data of these agents. Some conditions may also occur together, necessitating multiple treatments. Despite effective and early treatment, patients are at heightened risk for neurological sequela. The literature on seizures related to metabolic deficiencies for pediatric patients is limited but has some guidance on appropriate dosing and monitoring for agents to target specific deficiencies, which may help with narrowing antiepileptic therapies, reducing side effects, and improving neurodevelopmental outcomes and quality of life. The focus of this review is to discuss the pharmacotherapy, including the most updated published efficacy and safety data, involved in treating refractory epilepsy as a result of metabolic errors.

Structural and biochemical consequences of pyridoxine-dependent epilepsy mutations that target the aldehyde binding site of aldehyde dehydrogenase ALDH7A1

In humans, certain mutations in the gene encoding aldehyde dehydrogenase 7A1 are associated with pyridoxine-dependent epilepsy (PDE). Understanding the impact of PDE-causing mutations on the structure and activity of ALDH7A1 could allow for the prediction of symptom-severity and aid the development of patient-specific medical treatments. Herein, we investigate the biochemical and structural consequences of PDE missense mutations targeting residues in the aldehyde substrate binding site: N167S, P169S, A171V, G174V, and W175G. All but G174V could be purified for biochemical and X-ray crystallographic analysis. W175G has a relatively mild kinetic defect, exhibiting a fivefold decrease in k_cat with no change in K_m . P169S and N167S have moderate defects, characterized by catalytic efficiencies of 20- and 100-times lower than wild-type, respectively. A171V has a profound functional defect, with catalytic efficiency 2000-times lower than wild-type. The crystal structures of the variants are the first for any PDE-associated mutant of ALDH7A1. The structures show that missense mutations that decrease the steric bulk of the side chain tend to create a cavity in the active site. The protein responds by relaxing into the vacant space, and this structural perturbation appears to cause misalignment of the aldehyde substrate in W175G and N167S. The P169S structure is nearly identical to that of the wild-type enzyme; however, analysis of B-factors suggests the catalytic defect may result from altered protein dynamics. The A171V structure suggests that the potential for steric clash with Val171 prevents Glu121 from ion pairing with the amino group of the aldehyde substrate. ENZYMES: Aldehyde dehydrogenase 7A1 (EC1.2.1.31). DATABASES: Coordinates have been deposited in the Protein Data Bank under the following accession codes: 6O4B, 6O4C, 6O4D, 6O4E, 6O4F, 6O4G, 6O4H.

Diagnosis of seizures and encephalopathy using conventional EEG and amplitude integrated EEG

Seizures are more common in the neonatal period than at any other time of life, partly due to the relative hyperexcitability of the neonatal brain. Brain monitoring of sick neonates in the NICU using either conventional electroencephalography or amplitude integrated EEG is essential to accurately detect seizures. Treatment of seizures is important, as evidence increasingly indicates that seizures damage the brain in addition to that caused by the underlying etiology. Prompt treatment has been shown to reduce seizure burden with the potential to ameliorate seizure-mediated damage. Neonatal encephalopathy most commonly caused by a hypoxia-ischemia results in an alteration of mental status and problems such as seizures, hypotonia, apnea, and feeding difficulties. Confirmation of encephalopathy with EEG monitoring can act as an important adjunct to other investigations and the clinical examination, particularly when considering treatment strategies such as therapeutic hypothermia. Brain monitoring also provides useful early prognostic indicators to clinicians. Recent use of machine learning in algorithms to continuously monitor the neonatal EEG, detect seizures, and grade encephalopathy offers the exciting prospect of real-time decision support in the NICU in the very near future.

Potential identification of vitamin B6 responsiveness in autism spectrum disorder utilizing phenotype variables and machine learning methods

We investigated whether machine learning methods could potentially identify a subgroup of persons with autism spectrum disorder (ASD) who show vitamin B6 responsiveness by selected phenotype variables. We analyzed the existing data from our intervention study with 17 persons. First, we focused on signs and biomarkers that have been identified as candidates for vitamin B6 responsiveness indicators. Second, we conducted hypothesis testing among these selected variables and their combinations. Finally, we further investigated the results by conducting cluster analyses with two different algorithms, affinity propagation and k-medoids. Statistically significant variables for vitamin B6 responsiveness, including combination of hypersensitivity to sound and clumsiness, and plasma glutamine level, were included. As an a priori variable, the Pervasive Developmental Disorders Autism Society Japan Rating Scale (PARS) scores was also included. The affinity propagation analysis showed good classification of three potential vitamin B6-responsive persons with ASD. The k-medoids analysis also showed good classification. To our knowledge, this is the first study to attempt to identify subgroup of persons with ASD who show specific treatment responsiveness using selected phenotype variables. We applied machine learning methods to further investigate these variables' ability to identify this subgroup of ASD, even when only a small sample size was available.

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.

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

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

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.

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.

Current treatment and management of pyridoxine-dependent epilepsy

OPINION STATEMENT

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.

The Epileptic Encephalopathies of Infancy and Childhood

The epileptic encephalopathies comprise a group of devastating seizure syndromes which begin in infancy and early childhood and usually result in intractable epilepsy. While some syndromes are relatively easily diagnosed early in their course, others take time to evolve, hampering an early, confident diagnosis. Epileptic encephalopathies are associated with slowing of cognitive function and evolution of severe behavioral disorders, which are often more distressing to families than the epilepsy. While an underlying etiology may explain some of this co-morbidity, many children have no identifiable etiology found for their seizures. In these “idiopathic” cases, recurrent subtle seizures, frequent epileptiform discharge and non-convulsive status epilepticus probably all play a role in deterioration of cognitive function and evolution of behavior disorders. This paper will review the most common epileptic encephalopathy syndromes, discuss the cognitive and behavioral co-morbidities and review current therapeutic options.

Occasional seizures, epilepsy, and inborn errors of metabolism

Seizures are a common paediatric problem, with inborn errors of metabolism being a rare underlying aetiology. The clinical presentation of inborn errors of metabolism is often associated with other neurological symptoms, such as hypotonia, movement disorders, and cognitive disturbances. However, the occurrence of epilepsy associated with inborn errors of metabolism represents a major challenge that needs to be identified quickly; for some cases, specific treatments are available, metabolic decompensation might be avoided, and accurate counselling can be given about recurrence risk. Some clinical presentations are more likely than others to point to an inborn error of metabolism as the cause of seizures. Knowledge of important findings at examination, and appropriate biochemical investigation of children with seizures of uncertain cause, can aid the diagnosis of an inborn error of metabolism and ascertain whether or not the seizures are amenable to specific metabolic treatment.

Vitamin-responsive epileptic encephalopathies in children

Untreated epileptic encephalopathies in children may potentially have disastrous outcomes. Treatment with antiepileptic drugs (AEDs) often may not control the seizures, and even if they do, this measure is only symptomatic and not specific. It is especially valuable to identify potential underlying conditions that have specific treatments. Only a few conditions have definitive treatments that can potentially modify the natural course of disease. In this paper, we discuss the few such conditions that are responsive to vitamin or vitamin derivatives.

Compound heterozygosity of two functional null mutations in the ALPL gene associated with deleterious neurological outcome in an infant with hypophosphatasia

Hypophosphatasia (HPP) is a heterogeneous rare, inherited disorder of bone and mineral metabolism caused by different mutations in the ALPL gene encoding the isoenzyme, tissue-nonspecific alkaline phosphatase (TNAP). Prognosis is very poor in severe perinatal forms with most patients dying from pulmonary complications of their skeletal disease. TNAP deficiency, however, may also result in neurological symptoms such as neonatal seizures. The exact biological role of TNAP in the human brain is still not known and the pathophysiology of neurological symptoms due to TNAP deficiency in HPP is not understood in detail. In this report, we describe the clinical features and functional studies of a patient with severe perinatal HPP which presented with rapidly progressive encephalopathy caused by new compound heterozygous mutations in the ALPL gene which result in a functional ALPL "knock out", demonstrated in vitro. In contrast, an in vitro simulation of the genetic status of his currently asymptomatic parents who are both heterozygous for one mutation, showed a residual in vitro AP activity of above 50%. Interestingly, in our patient, the fatal outcome was due to progressive encephalopathy which was refractory to antiepileptic therapy including pyridoxine, rather than hypomineralization and respiratory insufficiency often seen in HPP patients. The patient's cranial MRI showed progressive cystic degradation of the cortex and peripheral white matter with nearly complete destruction of the cerebrum. To our knowledge, this is the first MRI-based report of a deleterious neurological clinical outcome due to a progressive encephalopathy in an infant harboring a functional human ALPL "knock out". This clinical course of disease suggests that TNAP is involved in development and may be responsible for multiple functions of the human brain. According to our data, a certain amount of residual TNAP activity might be mandatory for normal CNS function in newborns and early childhood.

Long-Term Follow-up of a Successfully Treated Case of Congenital Pyridoxine-Dependent Epilepsy

Autosomal recessive disorders affecting pyridoxine (vitamin B6) metabolism are a rare but well-recognized cause of neonatal seizures. Antiquitin deficiency, caused by mutations in ALDH7A1, is a disorder of the lysine degradation pathway causing accumulation of an intermediate that complexes with pyridoxal phosphate. Reports of long-term follow-up of neonatal pyridoxine-dependent seizures (PDS) remain scarce and prognostic information is varied. We report a case of PDS in a 47-year-old lady who originally presented shortly after birth in 1964. Pyridoxine replacement was successful and diagnostic confirmation was obtained later in life, initially by biochemical analysis of serum pipecolic acid. Subsequently we organized genetic analysis of ALDH7A1, which revealed compound heterozygous mutations. To our knowledge, this represents the longest duration of follow-up published to date.

Pyridoxine and pyridoxalphosphate-dependent epilepsies

To date we know of four inborn errors of autosomal recessive inheritance that lead to vitamin B6-dependent seizures. Among these, pyridoxine-dependent seizures due to antiquitin deficiency is by far the most common, although exact incidence data are lacking. In PNPO deficiency, samples have to be collected prior to treatment, while PDE, hyperprolinemia type II and congenital HPP can be diagnosed while on vitamin B6 supplementation. A vitamin B6 withdrawal for diagnostic purposes is nowadays only indicated in patients with a clear vitamin B6 response but normal biochemical work-up. In the presence of therapy-resistant neonatal seizures, early consideration of a vitamin B6 trial over 3 consecutive days is crucial in order to prevent irreversible brain damage. While PLP would be effective in all four disorders, pyridoxine fails to treat seizures in PNPO deficiency. As PLP is unlicensed within Europe and North America, pyridoxine is widely used as the first line drug, but if it is ineffective it should be followed by a trial with PLP, especially in neonates. As severe apnea has been described in responders, resuscitation equipment should be at hand during a first pyridoxine/PLP administration. Patients and parents have to be informed about the lifelong dependency and recurrence risks in forthcoming pregnancies.

Long-term outcome in pyridoxine-dependent epilepsy

AIM

The long-term outcome of the Dutch pyridoxine-dependent epilepsy cohort and correlations between patient characteristics and follow-up data were retrospectively studied.

METHOD

Fourteen patients recruited from a national reference laboratory were included (four males, 10 females, from 11 families; median age at assessment 6y; range 2y 6mo-16y). The following data were retrieved: sex; age at seizure onset; age at the start of pyridoxine therapy; level of urinary alpha-aminoadipic semialdehyde; antiquitin mutations; developmental milestones; evaluation of neurocognitive functioning and school career; magnetic resonance imaging (MRI) and electroencephalography (EEG) assessments.

RESULTS

Pyridoxine was started antenatally in two children, in the first week of life in five, in the first month of life in three, or after the first month of life (range 2.5-8mo) in four. No child was physically disabled; however, only five walked at 2 years of age. Mental development was delayed in most: median IQ or developmental index was 72 (SD 19). Pyridoxine monotherapy controlled seizures in 10 of 14 children, whereas four needed additional antiepileptic drugs. Seizure persistence, antiepileptic drugs (other than pyridoxine), EEG background, and epileptiform activity were not associated with outcome. On neonatal MRI, structural and white matter abnormalities occurred in five of eight children; on follow-up, the number of abnormal MRIs was increased. Delayed initiation of pyridoxine medication and corpus callosum abnormalities were significantly associated with unfavourable neurodevelopmental outcome, but normal follow-up imaging did not predict a good outcome.

INTERPRETATION

Outcome of patients with pyridoxine-dependent epilepsy remains poor. Individual outcome cannot be predicted by the evaluated characteristics. We suggest that collaborated research in structured settings could help to improve treatment strategies and outcome for pyridoxine-dependent epilepsy.

Neonatal neuroimaging findings in inborn errors of metabolism

Individually, metabolic disorders are rare, but overall they account for a significant number of neonatal disorders affecting the central nervous system. The neonatal clinical manifestations of inborn errors of metabolism (IEMs) are characterized by nonspecific systemic symptoms that may mimic more common acute neonatal disorders like sepsis, severe heart insufficiency, or neonatal hypoxic-ischemic encephalopathy. Certain IEMs presenting in the neonatal period may also be complicated by sepsis and cardiomyopathy. Early diagnosis is mandatory to prevent death and permanent long-term neurological impairments. Although neuroimaging findings are rarely specific, they play a key role in suggesting the correct diagnosis, limiting the differential diagnosis, and may consequently allow early initiation of targeted metabolic and genetic laboratory investigations and treatment. Neuroimaging may be especially helpful to distinguish metabolic disorders from other more common causes of neonatal encephalopathy, as a newborn may present with an IEM prior to the availability of the newborn screening results. It is therefore important that neonatologists, pediatric neurologists, and pediatric neuroradiologists are familiar with the neuroimaging findings of metabolic disorders presenting in the neonatal time period.

Pyridoxine-dependent epilepsy: an under-recognised cause of intractable seizures

Pyridoxine-dependent epilepsy (PDE) is a rare autosomal recessive disorder causing intractable seizures in neonates and infants. PDE patients are typically resistant to anti-epileptic treatment but respond to the administration of pyridoxine. Different seizure types have been reported in PDE, and episodes of status epilepticus are common. Electroencephalographic or neuroimaging abnormalities are not pathognomonic for this disorder. Intellectual disability is frequent at the follow-up. Recently, elevated urinary α-aminoadipic semialdehyde has been shown to be a reliable biomarker of this disorder, and mutations in the ALDH7A1 gene, encoding α-aminoadipic semialdehyde dehydrogenase, have been demonstrated in the large majority of PDE patients. However, early consideration of a pyridoxine trial remains the most important issue in a neonate or in an infant with intractable early onset seizures.

Long-term follow-up in two siblings with pyridoxine-dependent seizures associated with a novel ALDH7A1 mutation

Pyridoxine-dependent seizures (PDS) is a rare disorder characterized by seizures resistant to anticonvulsants but controlled by daily pharmacologic doses of pyridoxine. Mutations in the antiquitin (ALDH7A1) gene have recently reported to cause PDS in most of patients. We report the long-term follow-up in two PDS siblings carrying a novel ALDH7A1 mutation.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.

Pyridoxine dependent epilepsy and antiquitin deficiency: clinical and molecular characteristics and recommendations for diagnosis, treatment and follow-up

Antiquitin (ATQ) deficiency is the main cause of pyridoxine dependent epilepsy characterized by early onset epileptic encephalopathy responsive to large dosages of pyridoxine. Despite seizure control most patients have intellectual disability. Folinic acid responsive seizures (FARS) are genetically identical to ATQ deficiency. ATQ functions as an aldehyde dehydrogenase (ALDH7A1) in the lysine degradation pathway. Its deficiency results in accumulation of α-aminoadipic semialdehyde (AASA), piperideine-6-carboxylate (P6C) and pipecolic acid, which serve as diagnostic markers in urine, plasma, and CSF. To interrupt seizures a dose of 100 mg of pyridoxine-HCl is given intravenously, or orally/enterally with 30 mg/kg/day. First administration may result in respiratory arrest in responders, and thus treatment should be performed with support of respiratory management. To make sure that late and masked response is not missed, treatment with oral/enteral pyridoxine should be continued until ATQ deficiency is excluded by negative biochemical or genetic testing. Long-term treatment dosages vary between 15 and 30 mg/kg/day in infants or up to 200 mg/day in neonates, and 500 mg/day in adults. Oral or enteral pyridoxal phosphate (PLP), up to 30 mg/kg/day can be given alternatively. Prenatal treatment with maternal pyridoxine supplementation possibly improves outcome. PDE is an organic aciduria caused by a deficiency in the catabolic breakdown of lysine. A lysine restricted diet might address the potential toxicity of accumulating αAASA, P6C and pipecolic acid. A multicenter study on long term outcomes is needed to document potential benefits of this additional treatment. The differential diagnosis of pyridoxine or PLP responsive seizure disorders includes PLP-responsive epileptic encephalopathy due to PNPO deficiency, neonatal/infantile hypophosphatasia (TNSALP deficiency), familial hyperphosphatasia (PIGV deficiency), as well as yet unidentified conditions and nutritional vitamin B6 deficiency. Commencing treatment with PLP will not delay treatment in patients with pyridox(am)ine phosphate oxidase (PNPO) deficiency who are responsive to PLP only.

Novel mutations in pyridoxine-dependent epilepsy

PURPOSE

Pyridoxine-Dependent Epilepsy (PDE) is a rare autosomal recessive disease with neonatal seizures resistant to conventional anti-epileptic drugs. This metabolic disease has to be diagnosed early and treated to improve outcome. We report on two new mutations that open new prenatal prospects and suggest a new diagnostic procedure.

CASE REPORT

We describe PDE in a neonate carrying two novel mutations in the ALDH7A1 gene: c.[852_856delCTTAG] + [1230C > A]; p.[(Phe410Leu)] + p.[(Leu285CysfsX26)]. This case also illustrates that diagnosis could have been made without any pyridoxine withdrawal, thanks to the measurement of biomarkers. The patient was successfully treated with pyridoxine supplementation and currently shows normal neurological development.

Seizures and paroxysmal events: symptoms pointing to the diagnosis of pyridoxine-dependent epilepsy and pyridoxine phosphate oxidase deficiency

AIM

We report on seizures, paroxysmal events, and electroencephalogram (EEG) findings in four female infants with pyridoxine-dependent epilepsy (PDE) and in one female with pyridoxine phosphate oxidase deficiency (PNPO).

METHOD

Videos and EEGs were analysed and compared with videos of seizures and paroxysmal events archived from 140 neonates. PDE and PNPO were proven by complete control of seizures once pyridoxine or pyridoxal 5'-phosphate was administered and by recurrence when withdrawn. Mutations in the antiquitin gene were found in three patients and in the PNPO gene in one child.

RESULTS

Seizures began within 48 hours after birth in four newborns and at age 3 weeks in one. Frequent multifocal and generalized myoclonic jerks, often intermixed with tonic symptoms, abnormal eye movement, grimacing, or irritability, were observed in all infants with PDE and PNPO, but rarely in the other archived videos of neonates. EEGs were inconstant and frequently no discernable ictal changes were recorded during the seizures and the paroxysmal events. In addition, interictal EEGs were inconclusive, with normal and abnormal recordings. In older children tonic-clonic seizures, abnormal behaviour, inconsolable crying, frightened facial expression, sleep disturbance, loss of consciousness, paraesthesia, or intermittent visual symptoms were described during controlled and uncontrolled withdrawal or insufficient dosage.

INTERPRETATION

PDE or PNPO should be considered in infants with prolonged episodes of mixed multifocal myoclonic tonic symptoms, notably when associated with grimacing and abnormal eye movements.

Neonatal Seizures: When to Consider and How to Investigate for an Inborn Error of Metabolism

Seizures occur more frequently in the neonatal period than in the remainder of childhood. Neonatal seizures can have different aetiologies. Inborn errors of metabolism are rare causes of seizures in the newborn. However, they are an important cause of intractable neonatal seizures, accounting for 30% of cases. Diagnosis is necessary for timely institution of appropriate treatment and is important in determining clinical outcome. As these are genetic conditions, it allows for appropriate genetic counselling. We describe the clinical presentation of neonatal seizures and the investigation findings in symptomatic neonatal seizures and epilepsy syndromes that arise in the neonatal period. The approach in diagnosis and investigation of an underlying inborn error of metabolism is described and inborn errors of metabolism that are important causes of neonatal seizures are reviewed.

Antenatal treatment in two Dutch families with pyridoxine-dependent seizures

Incidental reports suggest that antenatal treatment of pyridoxine dependent seizures (PDS) may improve neurodevelopmental outcome of affected patients. Two families with PDS are reported, both with two affected siblings. Antenatal treatment with pyridoxine was instituted during the second pregnancy in each family (50 and 60 mg daily from 3 and 10 weeks of gestation, respectively). Perinatal characteristics and neurodevelopmental outcome at 4 (Family A) and 12 (Family B) years of age were compared between the untreated and treated child within each family. Meconium-stained amniotic fluid was present in both first pregnancies and abnormal foetal movements were noticed in one. In the treated infants, pregnancy and birth were uncomplicated. In family A, postnatal pyridoxine supplementation prevented neonatal seizures. Both children in family A were hypotonic and started walking after 2 years of age; both had white matter changes on MRI, and the first child was treated for squint. IQ was 73 and 98 in the antenatally untreated and treated child, respectively. The second child in family B developed seizures on the seventh day, because pyridoxine maintenance therapy had not been instituted after birth. Seizures responded rapidly to pyridoxine supplementation. MRI showed large ventricles and a mega cisterna magna. IQ was 80 and 106 in the antenatally untreated and treated child respectively. Both children had normal motor development. These results suggest that antenatal pyridoxine supplementation may be effective in preventing intrauterine seizures, decreasing the risk of complicated birth and improving neurodevelopmental outcome in PDS.

Clinical features and the management of pyridoxine-dependent and pyridoxine-responsive seizures: review of 63 North American cases submitted to a patient registry

To facilitate clinical research on pyridoxine-dependent seizures (PDS), a rare disease registry was established for affected patients in the United States and Canada. From 1999 to 2007, 63 cases, ranging in age from 11 months to 40 years, were registered. All registered cases were diagnosed with PDS by their physicians using clinical criteria. Seventy percent of the cases presented with neonatal seizures, and the mean lag time between presentation and diagnosis was 313 days. Pyridoxine treatment regimens were varied, ranging from 50 to 2,500 mg per day (1.4 to 67.8 mg/kg/day). While 47 of the cases were seizure-free on pyridoxine monotherapy, over time, eight other cases also required the concomitant use of anticonvulsants for effective seizure control, while the remainder continued to have recurrent seizures, despite the use of pyridoxine and multiple anticonvulsants. Our review of this collection of cases suggests that, for some registered individuals, either pyridoxine may be acting as an adjunctive anticonvulsant or the patient may have developed a secondary etiology for seizures. In addition, some of these cases may have pyridoxine-responsive seizures (PRS) rather than pyridoxine-dependency. Four adult and seven school-aged cases were described as developmentally normal, while the other cases had a variety of neurodevelopmental handicaps. Twenty-five percent of the cases required the pharmacologic treatment of behavioral symptoms. Clinicians caring for neonates and other young patients with intractable seizures do not necessarily consider PDS as an etiology; therefore, certain cases may be undiagnosed or diagnosed late in the course of their evaluation and treatment. As the diagnosis of PDS can now be confirmed by genetic and biochemical testing, formal screening protocols for this disorder should be developed. Patients previously diagnosed with PDS by clinical criteria should also receive confirmatory testing.

Two novel ALDH7A1 (antiquitin) splicing mutations associated with pyridoxine-dependent seizures

Pyridoxine-dependent seizures (PDS) is a rare autosomal recessive disorder causing intractable seizures in neonates and infants. Patients are typically resistant to conventional anticonvulsants but respond well to the administration of pyridoxine. We report two unrelated patients affected with PDS as a result of alpha-aminoadipic semialdehyde (alpha-AASA) dehydrogenase deficiency caused by pathogenic ALDH7A1/antiquitin mutations. Two of the three reported mutations are novel and result in erroneous splicing, as showed by messenger RNA (mRNA) studies. So far, the vast majority of the patients clinically diagnosed as PDS show alpha-AASA dehydrogenase deficiency, caused by mutations in the ALDH7A1 gene. However, despite the availability of reliable biomarkers, early consideration of a pyridoxine trial is still the most important issue in a child with therapy-resistant seizures.

New treatment paradigms in neonatal metabolic epilepsies

Neonatal seizures represent a major challenge among the epilepsies vis-à-vis seizure classification, electroclinical correlation, inherent excitability of neocortex, ontogenic characteristics of neurotransmitter receptors, and responsiveness to standard antiepileptic drugs. Each of these factors renders neonatal seizures more difficult to treat, and therapy has been a vexing area for recent advances in this seizure category. Conversely, specific metabolic disorders have very special therapeutic considerations in the clinical setting of neonatal seizures which require a high index of clinical suspicion and rapid intervention for a successful outcome. The prototype is pyridoxine dependency, although pyridoxal 5'-phosphate dependency is a recently recognized but treatable neonatal epilepsy that deserves earmarked distinction. Clinicians must remain vigilant for these possibilities, including atypical cases where apparent seizure-free intervals may occur. Folinic acid-dependent seizures are allelic with pyridoxine dependency. Serine-dependent seizures and glucose transporter deficiency may present with neonatal seizures and have specific therapy. A vital potassium channel regulated by serum ATP/ADP ratios in the pancreas and brain may be mutated with a resultant neuroendocrinopathy characterized by development delay, epilepsy, and neonatal diabetes (DEND). This requires oral hypoglycaemic therapy, and not insulin, for neurological responsiveness. The startle syndrome of hyperekplexia, which mimics neonatal epilepsy, has been associated with laryngospasm and sudden death but is treated with benzodiazepines.

Pyridoxine-dependent seizures caused by alpha amino adipic semialdehyde dehydrogenase deficiency: the first polish case with confirmed biochemical and molecular pathology

Pyridoxine-dependent seizures are a rare condition recognized when numerous seizures respond to pyridoxine treatment and recur on pyridoxine withdrawal. For decades the diagnosis was confirmed only with pyridoxine treatment withdrawal trial. Recently described biochemical and molecular pathology improved the diagnostic process for those cases in which seizures are caused by alpha amino adipic semialdehyde dehydrogenase deficiency. This article presents a girl with recurrent status epilepticus episodes resistant to phenobarbital and phenytoin and partly responding to midazolam. Eventually the seizures were completely controlled with pyridoxine; however, due to the severe condition of this child when seizing, no trial of withdrawal has been performed. The diagnosis of pyridoxine-dependent seizures was confirmed with biochemical and molecular testing revealing elevated alpha-AASA excretion and the presence of 2 different mutations in the antiquitin ( ALDH7A1) gene. Due to the availability of reliable laboratory testing, confirmation of the diagnosis was made without the life-threatening trial of pyridoxine withdrawal.

Treatable neonatal epilepsy

Perspective on the paper by Bok et al (see page 687)

Allelic and non-allelic heterogeneities in pyridoxine dependent seizures revealed by ALDH7A1 mutational analysis

Pyridoxine dependent seizure (PDS) is a disorder of neonates or infants with autosomal recessive inheritance characterized by seizures, which responds to pharmacological dose of pyridoxine. Recently, mutations have been identified in the ALDH7A1 gene in Caucasian families with PDS. To elucidate further the genetic background of PDS, we screened for ALDH7A1 mutations in five PDS families (patients 1-5) that included four Orientals. Diagnosis as having PDS was confirmed by pyridoxine-withdrawal test. Exon sequencing analysis of patients 1-4 revealed eight ALDH7A1 mutations in compound heterozygous forms: five missense mutations, one nonsense mutation, one point mutation at the splicing donor site in intron 1, and a 1937-bp genomic deletion. The deletion included the entire exon 17, which was flanked by two Alu elements in introns 16 and 17. None of the mutations was found in 100 control chromosomes. In patient 5, no mutation was found by the exon sequencing analysis. Furthermore, expression level or nucleotide sequences of ALDH7A1 mRNA in lymphoblasts were normal. Plasma pipecolic acid concentration was not elevated in patient 5. These observations suggest that ALDH7A1 mutation is unlikely to be responsible for patient 5. Abnormal metabolism of GABA/glutamate in brain has long been suggested as the underlying pathophysiology of PDS. CSF glutamate concentration was elevated during the off-pyridoxine period in patient 3, but not in patient 2 or 5. These results suggest allelic and non-allelic heterogeneities of PDS, and that the CSF glutamate elevation does not directly correlate with the presence of ALDH7A1 mutations.

Non-compliance in pyridoxine-dependent seizures and a way out

Pyridoxine dependency is a rare autosomal-recessive disorder causing intractable seizures in neonates and infants. Life-long therapy with pyridoxine is required for prevention of seizure recurrence and for an optimum intellectual outcome. With the availability of newer biochemical confirmatory tests, the conventional pyridoxine-withdrawal test is being used less frequently for diagnosis. This report describes an infant whose parents were non-compliant with pyridoxine therapy and proposes that pyridoxine-withdrawal test may be useful in demonstrating to parents the need for life-long pyridoxine therapy, thereby reducing non-compliance.

Pyridoxine-dependent seizures: a family phenotype that leads to severe cognitive deficits, regardless of treatment regime

The neuropsychological and clinical histories of three male siblings affected by pyridoxine-dependent seizures with known homozygous antiquitin mutations are presented. Neuropsychological evaluation is reported from when the siblings were 11, 9, and 7 years of age. Two of the siblings had received early pyridoxine treatment (antenatal, 2-4 wks into pregnancy) and one had received late treatment (2mo postnatal). However, there was no differential effect on cognitive outcome, with all three siblings having moderate to severe learning disability. Unlike previously reported cases that received early postnatal treatment, none of the siblings had relatively preserved non-verbal cognitive skills. Equally, their intellectual performance over time did not increase above the 1st centile despite high maintenance doses of vitamin B6 (range 16-26 mg/kg/d), and mild sensory neuropathy was reported on nerve conduction studies. The findings in these siblings challenge assumptions that early and high dose pyridoxine treatment can benefit cognition in this population and suggest routine electromyography monitoring may be beneficial.

Inborn errors affecting vitamin B6 metabolism

Vitamin B6 is an important vitamin for normal brain function. The metabolism of dietary vitamin B6 to its active cofactor pyridoxal 5´-phosphate is described. The mechanism of action of pyridoxal 5´-phosphate is described, as are some important functions in the brain. The clinical features and biochemistry of three inborn errors of metabolism affecting brain pyridoxal 5´-phosphate concentrations are described, each of which cause early-onset epilepsy of variable severity. These are pyridoxine phosphate oxidase deficiency, hyperprolinemia Type 2 and pyridoxine-dependent epilepsy caused by antiquitin deficiency. Hypophosphatasia is also discussed briefly, as the epilepsy that can complicate this disorder appears to be due to pyridoxal phosphate deficiency. Lastly, the antiepileptic properties of pyridoxine and pyridoxal phosphate are discussed.

Épilepsies néonatales et erreurs innées du métabolisme

Metabolic disorders constitute an important cause of neurologic disease, including neonatal epilepsy. Epilepsy rarely dominates the clinical presentation, which is more frequently associated with other neurologic symptoms, such as hypotonia and/or vigilance disturbances. In most cases, epilepsy secondary to inherited metabolic disorders presents with polymorphic clinical and electrographic features that are difficult to classify into precise epileptic syndromes. However, specific types of seizures, such as myoclonic seizures or distinctive electroencephalographic patterns, such as suppression burst patterns, epileptic syndrome or early myoclonic encephalopathy, may suggest a specific metabolic disease. The aim of this article is to help clinicians in reviewing potential metabolic diagnoses and approaching metabolic evaluations.

Epidemiology of pyridoxine dependent seizures in the Netherlands

BACKGROUND

Pyridoxine dependent epilepsy is a rare cause of seizures in childhood. The diagnosis is made on clinical criteria, that in many cases are never met. Therefore, epidemiological data on pyridoxine dependency are scarce.

AIMS

To study the epidemiology of pyridoxine dependent epilepsy in the Netherlands, and to determine whether the diagnosis is based on the appropriate criteria.

METHODS

Nationwide all departments of paediatrics (n = 113) and of paediatric or neonatal neurology (n = 17) were asked to report cases of pyridoxine dependent seizures. Birth incidences were calculated using national data on live births from 1991 to 2003.

RESULTS

Response was received from 67% of paediatric departments, including all university hospitals and 94% of child neurology departments. Thirteen patients were reported. Four definite (31%), three probable (23%), and four possible cases (31%) were identified. Two cases (15%) did not meet criteria for either of these groups. The birth incidence was 1:396,000 for definite and probable cases and 1:252,000 when possible cases are included.

CONCLUSIONS

Thus far, epidemiological data on pyridoxine dependent seizures were only available from the UK and Ireland. A higher incidence was found in the Netherlands, in accordance with earlier suggestions of a regional difference. The study shows that the diagnosis is often made without performance of a formal trial of withdrawal. The importance of confirming the diagnosis, concerning the consequences as for individual prognosis, the potential side effects of prolonged pyridoxine substitution, and the possibility of treating the mother in case of future pregnancies are emphasised.

Nonpharmacological treatment options for epilepsy

Approximately one third of children with epilepsy have persistent seizures despite trials of multiple antiepileptic medications. For some of these patients, epilepsy surgery may provide freedom from seizures. However, in many cases, epilepsy surgery is not a viable treatment option. Nonpharmacological approaches are a useful adjunct to help manage seizures in these children. This review examines the role of vagus nerve stimulation, the ketogenic diet, and various forms of EEG biofeedback therapy in children with intractable epilepsy. Although the mechanism of action is not known precisely for any of these adjunctive therapies, they add an important and evolving dimension to the management of difficult to control epilepsy in children. In addition, pyridoxine-dependent seizures are discussed as an example of an etiology of refractory seizures that responds well to replacement therapy.

Pyridoxal phosphate is better than pyridoxine for controlling idiopathic intractable epilepsy

AIM

To study the difference between pyridoxine (PN) and its active form, pyridoxal phosphate, (PLP) in control of idiopathic intractable epilepsy in children.

METHODS

Among 574 children with active epilepsy, 94 (aged 8 months to 15 years) were diagnosed with idiopathic intractable epilepsy for more than six months. All received intravenous PLP 10 mg/kg, then 10 mg/kg/day in four divided doses. If seizures recurred within 24 hours, another dose of 40 mg/kg was given, followed by 50 mg/kg/day in four divided doses. For those patients whose seizures were totally controlled, PLP was replaced by the same dose of oral PN. If the seizure recurred, intravenous PLP was infused followed by oral PLP 50 mg/kg/day.

RESULTS

Fifty seven patients had generalised seizures (of whom 13 had infantile spasms) and 37 had focal seizure. Eleven had dramatic and sustained responses to PLP; of these, five also responded to PN. Within six months of treatment with PLP or PN, five of the 11 patients were seizure free and had their previous antiepileptic medicine tapered off gradually. Two were controlled with pyridoxine and the other three needed PLP to maintain seizure freedom. The remaining six responders needed PLP exclusively for seizure control. Six of the 11 responders to PLP had infantile spasms (46%); four of them needed PLP exclusively. The other five responders were in the remaining 81 patients with other seizure type.

CONCLUSIONS

PLP could replace PN in the treatment of intractable childhood epilepsy, particularly in the treatment of infantile spasms.

Prevalence of pyridoxine dependent seizures in south Indian children with early onset intractable epilepsy: A hospital based prospective study

OBJECTIVES

Determine the prevalence of pyridoxine dependent seizures in children less than 16 years of age attending a teaching hospital in south India with early onset (before 3 years) intractable epilepsy of unknown aetiology, using the criteria proposed by Baxter.

METHOD

A cohort of 81 children, fulfilling the above criteria, was given 15 mg/kg/day of oral pyridoxine for 7 days. Non-responders were given a further 7-day trial of 30 mg/kg/day. Diagnosis of pyridoxine dependent seizures was made according to the criteria proposed by Baxter.

RESULT

Six children (7.4%; four boys and two girls) were identified as definite cases and were continued on B6, without recurrence of seizures. Median age of seizure onset and diagnosis were 2.5 months and 2 year 9 months, respectively. No significant complications were observed with B6 therapy.

CONCLUSION

Chance of identifying PDS is not low in a subpopulation of children with intractable early onset cryptogenic epilepsy using the criteria proposed by Baxter, which warrants a therapeutic trial with B6 in them.