Glutamate decarboxylase is not genetically linked to pyridoxine-dependent seizures

West Syndrome Is an Exceptional Presentation of Pyridoxine- and Pyridoxal Phosphate-Dependent Epilepsy: Data From a French Cohort and Review of the Literature

Objective: To characterize the electro-clinical presentation of patients with pyridoxine-dependent epilepsy (PDE) and pyridoxal phosphate (PLP)-dependent epilepsy in order to determine whether some of them could be diagnosed as de novo West syndrome, i. e., West syndrome that starts after the age of 2 months without other types of seizures (focal seizures for instance) before the onset of epileptic spasms. Methods: We analyzed data from an unpublished cohort of 28 genetically confirmed cases of PDE with antiquitine (ATQ) deficiency and performed a review of the literature looking for description of West syndrome in patients with either PDE with ATQ deficiency or PLP-dependent epilepsy with Pyridox(am)ine phosphate oxidase (PNPO) deficiency. Results: Of the 28 cases from the ATQ deficiency French cohort, 5 had spasms. In four cases, spasms were associated with other types of seizures (myoclonus, focal seizures). In the last case, seizures started on the day of birth. None of these cases corresponded to de novo West syndrome. The review of the literature found only one case of PNPO deficiency presenting as de novo West syndrome and no case of ATQ deficiency. Significance: The presentation of PDE- and PLP-dependent epilepsy as de novo West syndrome is so exceptional that it probably does not justify a systematic trial of pyridoxine or PLP. We propose considering a therapeutic trial with these vitamins in West syndrome if spasms are associated with other seizure types or start before the age of 2 months.

Neonatal Encephalopathies: A Clinical Perspective

Seizures are the most acute evident manifestation of central nervous system dysfunction in neonates. The incidence is higher in very low weight neonates, about 58/100 live births, as opposed to full-term infants, estimated about 3.5/100 live births. Neonatal seizures represent the clinical manifestation of a non-specific disorder of cortical cerebral dysfunction, which could lead to permanent brain injury. The etiology is multifactorial and requires a judicious assessment of each clinical scenario. The diagnosis and its management are further complicated as most neonatal seizures may have very subtle or no clinical changes and the diagnosis may be just based on EEG findings, so-called subclinical. The treatment is dependent on the etiology, but early and opportune intervention can prevent further brain damage and improve prognosis. Although early identification and treatment are essential, the diagnosis of neonatal seizures can be further complicated by the clinical presentations, possible etiologies, and treatments. Nevertheless, research studies and clinical evidence have shown that early treatment with anti-seizure medications can change the outcome.

Metabolic etiologies in West syndrome

West syndrome (WS) is an early life epileptic encephalopathy associated with infantile spasms, interictal electroencephalography (EEG) abnormalities including high amplitude, disorganized background with multifocal epileptic spikes (hypsarrhythmia), and often neurodevelopmental impairments. Approximately 64% of the patients have structural, metabolic, genetic, or infectious etiologies and, in the rest, the etiology is unknown. Here we review the contribution of etiologies due to various metabolic disorders in the pathology of WS. These may include metabolic errors in organic molecules involved in amino acid and glucose metabolism, fatty acid oxidation, metal metabolism, pyridoxine deficiency or dependency, or acidurias in organelles such as mitochondria and lysosomes. We discuss the biochemical, clinical, and EEG features of these disorders as well as the evidence of how they may be implicated in the pathogenesis and treatment of WS. The early recognition of these etiologies in some cases may permit early interventions that may improve the course of the disease.

Preliminary investigation of the use of newborn dried blood spots for screening pyridoxine-dependent epilepsy by LC-MS/MS

α-AASA and P6C were measured retrospectively in original newborn DBS of five patients with PDE using a LC-MS/MS method we developed previously. Both α-AASA and P6C were elevated markedly in the three newborn DBS stored at -20°C. At room temperature, α-AASA and P6C in DBS appeared stable for 3 days and then decreased by up to 70% after 14 days but remained much higher than control, indicating newborn screening for PDE is feasible.

Lysine metabolism in mammalian brain: an update on the importance of recent discoveries

The lysine catabolism pathway differs in adult mammalian brain from that in extracerebral tissues. The saccharopine pathway is the predominant lysine degradative pathway in extracerebral tissues, whereas the pipecolate pathway predominates in adult brain. The two pathways converge at the level of ∆(1)-piperideine-6-carboxylate (P6C), which is in equilibrium with its open-chain aldehyde form, namely, α-aminoadipate δ-semialdehyde (AAS). A unique feature of the pipecolate pathway is the formation of the cyclic ketimine intermediate ∆(1)-piperideine-2-carboxylate (P2C) and its reduced metabolite L-pipecolate. A cerebral ketimine reductase (KR) has recently been identified that catalyzes the reduction of P2C to L-pipecolate. The discovery that this KR, which is capable of reducing not only P2C but also other cyclic imines, is identical to a previously well-described thyroid hormone-binding protein [μ-crystallin (CRYM)], may hold the key to understanding the biological relevance of the pipecolate pathway and its importance in the brain. The finding that the KR activity of CRYM is strongly inhibited by the thyroid hormone 3,5,3'-triiodothyronine (T3) has far-reaching biomedical and clinical implications. The inter-relationship between tryptophan and lysine catabolic pathways is discussed in the context of shared degradative enzymes and also potential regulation by thyroid hormones. This review traces the discoveries of enzymes involved in lysine metabolism in mammalian brain. However, there still remain unanswered questions as regards the importance of the pipecolate pathway in normal or diseased brain, including the nature of the first step in the pathway and the relationship of the pipecolate pathway to the tryptophan degradation pathway.

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.

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.

Biomarkers aiding diagnosis of atypical presentation of pyridoxine-dependent epilepsy

A 2-year-old girl from a consanguineous marriage was evaluated for refractory seizures that had presented at birth. Since her presentation, she had been treated with pyridoxine and antiepileptic medications. Because she did not manifest the expected clinical response, pyridoxine was discontinued, which led to an increase in clinical events. Cerebrospinal fluid neurotransmitter metabolite chromatography and an assay of serum biomarkers, including pipecolic acid and α-aminoadipic semialdehyde, confirmed the diagnosis of pyridoxine-dependent epilepsy, and genetic testing identified a homozygous mutation in our patient, and in a first cousin with epilepsy. The reintroduction of pyridoxine and addition of folinic acid eventually led to control of her seizures. Early testing of biomarkers may prevent delays in diagnosing pyridoxine-dependent epilepsy. We recommend that all patients presenting with cryptogenic seizures before age 18 months undergo this evaluation.

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.

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.

The pediatric neurotransmitter disorders

The pediatric neurotransmitter disorders represent an enlarging group of neurological syndromes characterized by abnormalities of neurotransmitter synthesis and breakdown. The disorders of dopamine and serotonin synthesis are aromatic amino acid decarboxylase deficiency, tyrosine hydroxylase deficiency, and disorders of tetrahydrobiopterin synthesis. Amino acid decarboxylase, tyrosine hydroxylase, sepiapterin reductase, and guanosine triphosphate cyclohydrolase (Segawa disease) deficiencies do not feature elevated serum phenylalanine and require cerebrospinal fluid analysis for diagnosis. Segawa disease is characterized by dramatic and lifelong responsiveness to levodopa. Glycine encephalopathy is typically manifested by refractory neonatal seizures secondary to a defect of the glycine degradative pathway. gamma-amino butyric acid (GABA) metabolism is associated with several disorders, including glutamic acid decarboxylase deficiency with nonsyndromic cleft lip/ palate, GABA-transaminase deficiency, and succinic semialdehyde dehydrogenase deficiency. The latter is characterized by elevated gamma-hydroxybutyric acid and includes a wide range of neuropsychiatric symptoms as well as epilepsy. Pyridoxine-dependent seizures have now been associated with deficiency of alpha-aminoadipic semialdehyde dehydrogenase, as well as a new variant requiring therapy with pyridoxal-5-phosphate, the biologically active form of pyridoxine.

Diagnosis and treatment of neurotransmitter disorders

The neurotransmitter disorders represent an enigmatic and enlarging group of neurometabolic conditions caused by abnormal neurotransmitter metabolism or transport. A high index of clinical suspicion is important, given the availability of therapeutic strategies. This article covers disorders of monoamine (catecholamine and serotonin) synthesis, glycine catabolism, pyridoxine dependency, and gamma-aminobutyric acid (GABA) metabolism. The technological aspects of appropriate cerebrospinal fluid (CSF) collection, shipment, study, and interpretation merit special consideration. Diagnosis of disorders of monoamines requires analysis of CSF homovanillic acid, 5-hydroxyindoleacetic acid, ortho-methyldopa, BH4, and neopterin. The delineation of new disorders with important therapeutic implications, such as cerebral folate deficiency and PNPO deficiency, serves to highlight the value of measuring CSF neurotransmitter precursors and metabolites. The impressive responsiveness of Segawa fluctuating dystonia to levodopa is a hallmark feature of previously unrecognized neurologic morbidity becoming treatable at any age. Aromatic amino acid decarboxylase and tyrosine hydroxylase deficiency have more severe phenotypes and show variable responsiveness to levodopa. Glycine encephalopathy usually has a poor outcome; benzoate therapy may be helpful in less affected cases. Pyridoxine-dependent seizures are a refractory but treatable group of neonatal and infantile seizures; rare cases require pyridoxal-5-phosphate. Succinic semialdehyde dehydrogenase deficiency is relatively common in comparison to the remainder of this group of disorders. Treatment directed at the metabolic defect with vigabatrin has been disappointing, and multiple therapies are targeted toward specific but protean symptoms. Other disorders of GABA metabolism, as is true of the wide spectrum of neurotransmitter disorders, will require increasing use of CSF analysis for diagnosis, and ultimately, treatment.

Pyridoxine-dependent seizures: new genetic and biochemical clues to help with diagnosis and treatment

PURPOSE OF REVIEW

Pyridoxine dependency is an uncommon but important cause of intractable seizures presenting in infancy and early childhood. This paper discusses recent clinical, biochemical and genetic studies and how the findings should change our approach in evaluating young patients with antiepileptic drug-resistant seizures.

RECENT FINDINGS

Originally thought to be due to abnormal binding of pyridoxal phosphate to glutamic acid decarboxylase resulting in decreased gamma-aminobutyric acid, mutations in the gene encoding this enzyme have been ruled out. While linkage to 5q31 has been demonstrated, a disease-causing gene in that region has not been identified. Further haplotype analysis of six affected kindreds has demonstrated genetic heterogeneity for this rare disorder. Other studies demonstrate that some children with intractable seizures respond to pyridoxal phosphate rather than pyridoxine, including a rare form of neonatal epileptic encephalopathy shown to be due to mutations in the PNPO gene for pyridox(am)ine 5'-phosphate oxidase. While the biochemical explanation for this finding is not clear, elevated pipecolic acid levels may serve as a diagnostic marker for patients with pyridoxine-dependent seizures.

SUMMARY

The results of these studies should prompt clinicians to adopt new strategies for diagnosis and therapy for young patients with intractable seizures. Levels of both pipecolic acid and certain metabolites shown to be elevated in patients with PNPO mutations should be measured, and therapeutic trials of pyridoxal phosphate as well as pyridoxine should be considered early in the course of the management of infants and young children with intractable seizures.

Inherited disorders of neurotransmitters in children and adults

Inherited disorders of neurotransmitters are a group of neurometabolic syndromes attributable to a primary disturbance of neurotransmitter metabolism or transport. This is an enlarging group of recognized disorders requiring specialized diagnostic procedures for detection. This review considers clinical disorders of biopterin, catecholamines, serotonin, glycine, pyridoxine, and GABA metabolism. Newly described syndromes such as cerebral folate deficiency and pyridoxal-5-phosphate dependency are included. The disorders of the metabolic pathways of biopterin, catecholamines, and serotonin are linked due to their common synthetic components. Glycine encephalopathy represents an enlarging phenotype related to abnormalities of the glycine degradative cleavage system. Both pyridoxine and pyridoxal-5-phosphate dependency need to be considered in refractory neonatal seizures. The most common disorder of GABA metabolism is SSADH deficiency, which has a broad phenotype of mental retardation, epilepsy, ataxia, and hyporeflexia and which invokes the combined problems of elevated brain GABA and GHB.

Genetic heterogeneity for autosomal recessive pyridoxine-dependent seizures

Pyridoxine-dependent seizure (PDS) is a rare autosomal recessive intractable seizure disorder only controlled by a daily supplementation of pharmacological doses of pyridoxine (Vitamin B6). Although glutamate decarboxylase utilizes pyridoxal phosphate as a cofactor during conversion of the excitatory amino acid, glutamate, to the inhibitory neurotransmitter, gamma-amino butyric acid (GABA), several studies have failed to demonstrate a linkage to either of the glutamate-decarboxylase-encoding genes (GAD1 and GAD2) and PDS excluding involvement of this functional candidate. However, in 2000, a locus for PDS was mapped to a 5 cM interval at chromosome 5q31 in four consanguineous and one multisib pedigree (Z(max)=8.43 at theta=0 for marker D5S2017) [Cormier-Daire et al. in Am J Hum Genet 67(4):991-993 2000]. We undertook molecular genetic studies of six nonconsanguineous North American families, using up to ten microsatellite markers to perform haplotype segregation analysis of the 5q31 locus. Assignment to the chromosome 5q PDS locus was excluded in one of the six North American PDS pedigrees, as chromosome 5q31 haplotypes were incompatible with linkage to this locus. The remaining five PDS pedigrees showed haplotype segregation consistent with linkage to 5q31, generating a maximum combined lod score of 1.87 (theta=0) at marker D5S2011. In this study, we establish genetic heterogeneity for PDS, catalog 21 genes within the originally defined PDS interval, and identify additional recombinations that indicate a higher priority interval, containing just 11 genes.

Focal status epilepticus as atypical presentation of pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy usually presents in the neonatal period or even in utero, is refractory to antiepileptic medications, and is treatable with lifelong administration of pyridoxine. The seizures are typically generalized tonic-clonic, although myoclonic seizures or infantile spasms have been described. We report an infant who presented at 5 months of age with a right-sided clonic seizure with fever. Subsequently, she had recurrent right focal or generalized seizures despite sequential treatment with various antiepileptic medications. At 7 months, she was hospitalized with status epilepticus, which was finally controlled with pyridoxine. After she became seizure free, she continued to have a strong left arm preference with mild weakness of the right arm and delayed language skill. Eventually, she outgrew these symptoms. This case illustrates that pyridoxine-dependent epilepsy, although rare, must be included in the differential diagnosis of focal seizures, especially when the seizures are refractory to traditional antiepileptic drugs.

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.

Pipecolic acid concentrations in brain tissue of nutritionally pyridoxine-deficient rats

Elevated concentrations of pipecolic acid have been reported in plasma and CSF of patients with pyridoxine-dependent epilepsy, but its molecular background is unclear. To investigate any further association of pyridoxine and pipecolic acid metabolism, we have performed an animal trial and have measured the concentration of pipecolic acid in brain tissue of rats with nutritional pyridoxine deficiency and in control littermates. Concentrations of pyridoxal phosphate were significantly reduced in brain tissue of pyridoxine-deficient rats (p < 0.001), while concentrations of pipecolic acid were not significantly different from the normally nourished control group (p = 0.3). These data indicate that a direct association of pyridoxine and pipecolic acid metabolism is unlikely. We therefore assume that the characteristic elevation of pipecolic acid in pyridoxine-dependent epilepsy could rather be a secondary phenomenon with the primary defect of pyridoxine-dependent epilepsy being located outside the pipecolic acid pathway.

Clinical aspects of the disorders of GABA metabolism in children

PURPOSE OF REVIEW

There has been increased recognition of the pediatric neurotransmitter disorders. This review focuses on the clinical disorders of GABA metabolism.

RECENT FINDINGS

The known clinical disorders of GABA metabolism are pyridoxine dependent epilepsy, GABA-transaminase deficiency, SSADH deficiency, and homocarnosinosis. Pyridoxine dependent epilepsy is diagnosed clinically but potentially more common presentations, with later and atypical features, widen the spectrum. No gene locus has been confirmed; the pathophysiology may involve alterations in PLP transport, binding to GAD, or other PLP-dependent pathways. SSADH deficiency is associated with developmental delay, prominent language deficits, hypotonia, ataxia, hyporeflexia, and seizures. Increased detection is reported when specific ion monitoring is used for GHB on urine organic acids. The most consistent MRI abnormality is increased signal in the globus pallidus. MR spectroscopy has demonstrated the first example of increased endogenous GABA in human brain parenchyma in this disorder. GABA-transaminase deficiency and homocarnosinosis appear to be very rare but require CSF for detection, thus allowing for the possibility that these entities, as in the other pediatric neurotransmitter disorders, are underrecognized.

SUMMARY

The disorders of GABA metabolism require an increased index of clinical suspicion. Pyridoxine dependent epilepsy is a treatable condition with a potentially widening clinical spectrum, but with a prognosis dependent on early intervention. SSADH deficiency has a heterogeneous spectrum and requires careful urine organic acid testing for screening, followed by enzymatic confirmation allowing appropriate prognostic and genetic counseling.

Pyridoxine-dependent seizures: a clinical and biochemical conundrum

Pyridoxine-dependent seizures have been recognised for 40 years, but the clinical and biochemical features are still not understood. It is a rare recessively inherited condition where classically a baby starts convulsing in utero and continues to do so after birth, until given pyridoxine. Many of these early onset cases also have an acute encephalopathy and other clinical features. Late onset cases are now recognised with a less severe form of the condition. Seizures can break through with intercurrent illness but otherwise remain controlled on pharmacologic doses of pyridoxine. The long-term outcome is affected by several factors including whether onset is early or late and how soon pyridoxine is given. Biochemical studies have been sparse, on very small numbers. There does not appear to be any defect in the uptake or metabolism of pyridoxine or pyridoxal phosphate (PLP). For a long time glutamic acid decarboxylase (GAD), a pyridoxal-dependent enzyme, has been suspected to be the abnormal gene product, but glutamate and gamma-aminobutyric acid (GABA) studies on the cerebrospinal fluid (CSF) have been contradictory and recent genetic studies have not found any linkage to the two brain isoforms. A recent report describes raised pipecolic acid levels in patients but how this ties in is unexplained.

Pyridoxine-dependent seizures: findings from recent studies pose new questions

Pyridoxine-dependent seizures, although a rare clinical entity, have been recognized as an etiology of intractable seizures in neonates and infants for more than 45 years. Recent research has focused on the molecular and neurochemical aspects of this disorder, as well as the optimal treatment of the condition. This review discusses the clinical features and management of patients with pyridoxine-dependent seizures together with a new hypothesis suggesting that an abnormality of pyridoxine transport may underlie the pathophysiology of this autosomal-recessive disorder.

Inherited epilepsies

Epilepsy may be acquired or inherited. At least one half of epilepsy is genetic in origin; this figure is likely higher in children regardless of whether seizures are generalized or partial. Inherited epilepsies are classified as benign, cryptogenic, or symptomatic depending on associated clinical, electrographic, and neuroimaging features. To date, genetic mutations in the idiopathic inherited epilepsies affect channel function within the central nervous system; genes underlying symptomatic epilepsies are more heterogeneous. Accurate diagnosis of an inherited epilepsy syndrome provides useful prognostic information; it also may help guide diagnostic evaluation, including request for specific gene testing. In the near future, the relationship between genetic defect and response to specific anticonvulsants may also be better defined.