Pyridoxol metabolism in vitamin B6-responsive convulsions of early infancy

Super-Refractory Status Epilepticus: Prognosis and Recent Advances in Management

Super-refractory status epilepticus (SRSE) is a life-threatening neurological emergency with high morbidity and mortality. It is defined as “status epilepticus (SE) that continues or recurs 24 hours or more after the onset of anesthesia, including those cases in which SE recurs on the reduction or withdrawal of anesthesia.” This condition is resistant to normal protocols used in the treatment of status epilepticus and exposes patients to increased risks of neuronal death, neuronal injury, and disruption of neuronal networks if not treated in a timely manner. It is mainly seen in patients with severe acute onset brain injury or presentation of new-onset refractory status epilepticus (NORSE). The mortality, neurological deficits, and functional impairments are significant depending on the duration of status epilepticus and the resultant brain damage. Research is underway to find the cure for this devastating neurological condition. In this review, we will discuss the wide range of therapies used in the management of SRSE, provide suggestions regarding its treatment, and comment on future directions. The therapies evaluated include traditional and alternative anesthetic agents with antiepileptic agents. The other emerging therapies include hypothermia, steroids, immunosuppressive agents, electrical and magnetic stimulation therapies, emergent respective epilepsy surgery, the ketogenic diet, pyridoxine infusion, cerebrospinal fluid drainage, and magnesium infusion. To date, there is a lack of robust published data regarding the safety and effectiveness of various therapies, and there continues to be a need for large randomized multicenter trials comparing newer therapies to treat this refractory condition.

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.

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.

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.

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 epilepsy: a suggestive electroclinical pattern

AIMS

To determine if there is an electroencephalographic pattern suggestive of pyridoxine dependent epilepsy that could be used to improve the chances of early diagnosis.

METHODS

A retrospective study was made of all the clinical records and electroencephalograms of neonates identified with pyridoxine dependent seizures between 1983 and 1994, at this hospital. Neonates whose seizures began after more than 28 days of life were excluded; in all, five patients from four families were studied. Follow up ranged from 2 to 10 years.

RESULTS

A history of miscarriage and neonatal death during an epileptic seizure had occurred in the siblings of two families. One mother reported rhythmic movements of her child during the last month of pregnancy. At birth, all babies were hypotonic; four had decreased visual alertness. All babies were agitated, irritable, jittery, hyperalert, and exhibited sleeplessness and a startle reaction to touch and sound. Age of onset of seizures varied from 30 minutes to 3 days. Seizures of various types were recorded in all cases on EEG tracings, including spasms, myoclonic seizures, partial clonic, and secondary generalised seizures. Burst-suppression patterns occurred in three cases, and a combination of continuous and discontinuous patterns in two others. Bilateral high voltage delta slow wave activity was observed in four patients. Psychomotor delay was severe in three patients, moderate in one, and mild in one.

CONCLUSIONS

There is an identifiable EEG pattern that is highly suggestive of pyridoxine dependent epilepsy. Pyridoxine dependent epilepsy is probably underdiagnosed.

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

A regional population-based survey identified six patients with pyridoxine dependency. Four presented on the first day of life and the other two at 1 and 8 months of age. Apart from multiple seizure types, other presenting features included jitteriness; encephalopathy, at first thought to be hypoxic-ischaemic; hepatomegaly, and abdominal distension with bilious vomiting. Later problems included break-through fits with fever; transient visual agnosia; squint; severe articulatory apraxia; motor delay with later dyspraxia; macrocephaly, and post-haemorrhagic hydrocephalus. Magnetic resonance imaging showed variable structural abnormalities in all the early onset cases. Psychometric assessment revealed a stereotyped pattern of intelligence scale subtest scores, with a specific impairment of expressive verbal ability. In a prospective open study over one year, an increased dose of pyridoxine was associated with an improvement in IQ, particularly in performance subtests. Pyridoxine dependency is more common than has been thought. It has a wider range of clinical features than the classical neonatal seizures and causes specific impairments of higher function, some of which may be reversible. The dosage of pyridoxine should be optimal for IQ as well as seizure control.

Pyridoxine-dependent seizures: report of a case with atypical clinical features and abnormal MRI scans

A Japanese girl with atypical pyridoxine-dependent seizures is reported. Until 9 months of age the seizures had been controlled by conventional anticonvulsants. The initial administration of pyridoxine was followed by a collapse; the suppression-burst pattern changed to an almost flat pattern in the EEG. T1- and T2-weighted magnetic resonance imaging (MRI) scans showed poor differentiation between white and gray matter, and T2-weighted MRI scans showed periventricular hyperintensity areas adjacent to the posterior horns of lateral ventricles. The findings in this patient indicate that pyridoxine should be given to infants with intractable epilepsy, regardless of the response to anticonvulsants, and that resuscitation facilities should be available during such a trial.

Pyridoxine-dependent seizures, clinical and therapeutic aspects

Pyridoxine-dependency is a rare autosomal recessive disorder causing a severe seizure disorder of prenatal or neonatal onset, psychomotor retardation and death in untreated patients. Treatment requires life-long supplementation with pyridoxine (vitamin B6). The underlying defect is unknown, and there is no biological marker for the disease. Clinical diagnosis is often delayed and severe neurological sequelae are common. This article summarizes both clinical and therapeutic aspects.

Pyridoxine-dependent epilepsy: EEG investigations and long-term follow-up

The EEG features and clinical correlates were investigated before, directly after, and on long-term follow-up after initiation of pyridoxine therapy in 6 patients with B6-dependent epilepsy. At each phase, the EEG provided important diagnostic and prognostic information. Pre-B6 3 neonates manifested a unique EEG pattern of generalized bursts of 1-4 Hz sharp and slow activity. This pattern has not been previously described in neonates with B6 dependency and in this age group appears to be highly suggestive of the diagnosis. Five patients experienced an apparent initial response to traditional antiepileptics. The parenteral pyridoxine test, performed in all 5, and repeated in 3, proved to be a highly reliable and reproducible diagnostic test. After 50-100 mg of B6 there was cessation of clinical seizures within minutes and of paroxysmal discharges within hours. On long-term follow-up (3-28 years) all 6 patients were seizure free on B6 (10-100 mg/day) monotherapy. Recurrences of seizures and of specific sequential EEG changes (background slowing, photoparoxysmal response, spontaneous discharges, stimulus-induced myoclonus, generalized seizures) occurred upon B6 withdrawal. Long-term prognosis correlated with the EEG. Two patients had persistently abnormal EEG backgrounds and were moderately to severely retarded, while 4 had normal EEGs with normal or near normal development.

Protoporphyrinaemia and decreased activities of 5-aminolevulinic acid dehydrase and uroporphyrinogen I synthetase in erythrocytes of a Vitamin B6-deficient epileptic boy given valproic acid and carbamazepine

Carbamazepine (CBMZP) has been implicated as an inhibitor of the activities of 5-aminolaevulinic acid dehydratase (ALA-D) and uroporphyrinogen I synthetase (URO-S). In an epileptic boy undergoing long-term treatment with valproic acid (VPA), 1.3 g/d, CBMZP, 0.9 g/d and folic acid, 7.5 mg/d, decreased activities of ALA-D and URO-S coincided with increased levels of erythrocyte protoporphyrin (EP) in the absence of Pb poisoning, iron depletion and erythropoietic protoporphyria. A progressive fall in plasma pyridoxal 5'-phosphate (B6-P) to 7.7 nmol/L (lower reference limit, 14.6 nmol/L) prompted implementation of pyridoxine HCl (B6-HCl), 87.5 mg/d followed by administration of both B6-HCl and preformed B6-P (50 mg/d each). This permitted the eventual withdrawal of VPA and a net reduction of CBMZP to 450 mg/d. During these manipulations, ALA-D and URO-S activities, EP and urinary porphyrins and their precursors were measured serially. An assay system utilizing red cell ALA-D for generation of porphobilinogen (PBG) from added ALA at pH 7.4 was used for determination of ALA-D and URO-S activities in separate aliquots of the same assay mixture both in the absence and presence of Zn and dithiothreitol (DTT). One unit (U) for ALA-D = 1 nmol PBG/L RBC/s; for URO-S = 1 nmol porphyrin/L/s; minimum normal level for ALA-D = 135 U; for URO-S = 6 U. B6-HCl alone entailed increases in ALA-D and URO-S prior to any reduction of CBMZP. After administration of both B6-HCl and B6-P and withdrawal of VPA, the overall increase in ALA-D was from 54.59 to 197.2 U (-Zn; -DTT) and from 50.76 to 217.3 U (+Zn; +DTT). The overall increase in URO-S was from 2.67 to 8.90 U (-Zn; -DTT) and from 3.02 to 8.66 U (+Zn; +DTT). During stepwise reduction of VPA, EP remained elevated to values as high as 2.48 mumol/L (upper reference limit, 1.33 mumol/L). Only after permanent withdrawal of VPA did concentrations of EP fall to normal levels. Values for porphyrins and their precursors in urine were normal throughout. Since both VPA and B6-P are strongly protein-bound, it is suggested that VPA displaced B6-P from protective protein binding sites and that the resulting deficit in B6-P (rather than CBMZP) reduced ALA-D and URO-S activities via primary reduction of ALA-synthetase activity. Increases in EP emerge as a hitherto unappreciated effect of VPA warranting further investigation.

Pyridoxine for neonatal seizures: an unexpected danger

A case of pyridoxine-dependent seizures is reported. Administration of pyridoxine to an infant after a long period of convulsions was followed by acute hypotonia. Other cases have been reported in the literature, in one of which assisted ventilation was required. A possible mechanism for this alarming outcome is discussed, and it is suggested that resuscitation facilities should be quickly available during such trials.

Atypical presentations of pyridoxine-dependent seizures: a treatable cause of intractable epilepsy in infants

We report on 3 patients with atypical pyridoxine-dependent seizures. Each had either late onset of convulsions (2 cases) or seizure-free intervals of up to several months' duration in the absence of pyridoxine supplementation. The findings, taken together with those in 9 previously reported cases, indicate that a trial of pyridoxine should be performed in all seizure disorders with onset before 18 months of age, regardless of type.

A fluorimetric method for the measurement of pyridoxal and pyridoxal phosphate in human plasma and leucocytes, and its application to patients with sideroblastic marrows

A highly sensitive fluorimetric assay for the measurement of pyridoxal and pyridoxal phosphate in biological tissues is described. The method involves the enzymic hydrolysis of pyridoxal phosphate to pyridoxal. The pyridoxal (free or total) is separated on an anion-exchange column, concentrated by cation-exchange chromatography and reacted with potassium cyanide under slightly alkaline conditions to form 4-pyridoxolactone, a highly fluorescent compound. The method is applied to the measurement of pyridoxal, pyridoxal phosphate and total pyridoxal in plasma and neutrophils from control subjects and patients with sideroblastic marrow and identified the patient with pyridoxine-responsive sideroblastic anaemia.

Pyridoxine dependent seizures--a wider clinical spectrum

We report 4 infants with pyridoxine dependent seizures who had clinical features that led to diagnostic uncertainty. Their clinical course was unusual in 1 or more of the following: later onset of initial seizures; a seizure free period after taking of anticonvulsants, but before taking of pyridoxine; a long remission after withdrawal of pyridoxine; and atypical seizure type. This report illustrates a broader range of clinical features and highlights the need to consider the diagnosis of pyridoxine dependent seizures in any infant with intractable epilepsy, regardless of the pattern of seizures and the response to anticonvulsant medications. In such a case, 100 mg intravenous pyridoxine should be given and, if a definite clinical response is established, oral pyridoxine should be continued indefinitely.

Pyridoxine-dependency seizure: report of a rare presentation

A child developed minor motor seizures at the age of 14 months accompanied by an abnormal electroencephalogram showing single spikes and polyspikes over the vertex and frontocentral regions. Seizures continued until the age of 22 months despite administration of several standard anticonvulsants. At age 22 months, pyridoxine, 75 mg daily, was initiated and anticonvulsants were discontinued. Both the seizures and the electroencephalographic abnormality have disappeared over the ensuing 20 months with pyridoxine therapy.

Drug-pyridoxal phosphate interactions

In this review it has been pointed out that vitamin B6 and its vitamers can be involved in many interactions with a number of drugs, as well as with the actions of various endocrines and neurotransmitters. Nutritional deficiencies, especially of vitamins and proteins, can affect the manner in which drugs undergo biotransformation, and thereby may also modify the therapeutic efficacy of certain drugs. The differences between nutritional vitamin B6 deficiency and the hereditary disorder producing pyridoxine dependency are discussed. In addition to a pyridoxine deficiency being able to adversely affect drug actions, the improper supplementation with vitamin B6 can in some instances also adversely affect drug efficacy. A decrease by pyridoxine in the efficacy of levodopa used in the treatment of Parkinsonism is an example. The interrelationships and enzymatic interconversions among pyridoxine vitamers, both phosphorylated and non-phosphorylated, are briefly discussed, particularly regarding their pharmacokinetic properties. The ways in which the normal biochemical functions of vitamin B6 may be interfered with by various drugs are reviewed. (1) The chronic administration of isoniazid for the prevention or treatment of tuberculosis can produce peripheral neuropathy which can be prevented by the concurrent administration of pyridoxine. An acute toxic overdose of isoniazid causes generalized convulsions, and the intravenous administration of pyridoxine hydrochloride will prevent or stop these seizures. (2) The acute ingestion of excessive monosodium glutamate will, in some individuals, cause a group of symptoms including among others headache, weakness, stiffness, and heartburn, collectively known as the 'Chinese Restaurant Syndrome.' These symptoms can be prevented by prior supplementation with vitamin B6. The beneficial effect is ascribed to the correction of a deficiency in the activity of glutamic oxaloacetic transaminase, an enzyme that is dependent on pyridoxal phosphate. Some interesting relationships are pointed out between vitamin B6, picolinic acid, and zinc. It is postulated that the intestinal absorption of zinc is facilitated by picolinic acid, a metabolite of tryptophan. The derivation of picolinic acid from tryptophan depends on the action of the enzyme kynureninase, which is dependent on pyridoxal phosphate; therefore, the adequate absorption of zinc is indirectly dependent on an adequate supply of vitamin B6. The formation of pyridoxal phosphate, on the other hand, appears to be indirectly dependent on Zn2++ which activates pyridoxal kinase.(ABSTRACT TRUNCATED AT 400 WORDS)

Subcellular localization and properties of pyridoxal phosphate phosphatases of human polymorphonuclear leukocytes and their relationship to acid and alkaline phosphatase

Using a novel fluorimetric assay for pyridoxal phosphate phosphatase, human polymorphonuclear leucocytes were found to exhibit both acid an alkaline activities. The neutrophils were homogenised in isotonic sucrose and subjected to analytical subcellular fractionation by sucrose density gradient centrigfugation. The alkaline pyridoxal phosphate phosphatase showed a very similar distribution to alkaline phosphatase an was located solely to the phosphasome granules. Fractionation experiments on neutrophils treated with isotonic sucrose containing digitonin and inhibitor studies with diazotised sulphanilic acid and levamisole further confirmed that both enzyme activities had similar locations and properties. Acid pyridoxal phosphate phosphatase activity was located primarily to the tertiary granule with a partial azurophil distribution. Fractionation studies on neutrophils homogenised in isotonic sucrose containing digitonin and specific inhibitor studies showed that acid pyridoxal phosphate phosphatase and acid phosphatase were not the result of a single enzyme activity, Neutrophils were isolated from control subjects, patients with chronic granulocytic leukaemia and patients in the third trimester of pregnancy. The specific activities (munits/mg protein) of alkaline pyridoxal phosphate phosphatase an alkaline phosphatase varied widely in the three groups and the alterations occurred in a parallel manner. The specific activities of acid pyridoxal phosphate phosphatase and of acid phosphatase were similar in the three groups. These results, together with the fractionation experiments and inhibition studies strongly suggest that pyridoxal phosphate is a physiological substrate for neutrophil alkaline phosphatase.

A highly sensitive fluorimetric assay for pyridoxal phosphate phosphatase

A highly sensitive fluorimetric assay for pyridoxal phosphate phosphatase is described. The assay involves separation of the substrate and product by ion-exchange chromatography followed by treatment of pyridoxal with potassium cyanide under slightly alkaline conditions to form 4-pyridoxolactone, a highly fluorescent compound. Certain kinetic properties of the enzyme activities in human neutrophils are described.