A novel null mutation in the pyruvate dehydrogenase phosphatase catalytic subunit gene (PDP1) causing pyruvate dehydrogenase complex deficiency

Congenital lactic acidosis due to pyruvate dehydrogenase phosphatase (PDP) deficiency is very rare. PDP regulates pyruvate dehydrogenase complex (PDC) and defective PDP leads to PDC deficiency. We report a case with functional PDC deficiency with low activated (+dichloroacetate) and inactivated (+fluoride) PDC activities in lymphocytes and fibroblasts, normal activity of other mitochondrial enzymes in fibroblasts, and novel biallelic frameshift mutation in the PDP1 gene, c.575dupT (p.L192FfsX5), with absent PDP1 product in fibroblasts. Unexpectedly, the patient also had low branched-chain 2-ketoacid dehydrogenase (BCKDH) activity in fibroblasts with slight elevation of branched-chain amino acids in plasma and ketoacids in urine but with no pathogenic mutations in the enzymes of BCKDH, which could suggest shared regulatory function of PDC and BCKDH in fibroblasts, potentially in other tissues or cell types as well, but this remains to be determined. The clinical presentation of this patient overlaps that of other patients with primary-specific PDC deficiency, with neonatal/infantile and childhood lactic acidosis, normal lactate to pyruvate ratio, elevated plasma alanine, delayed psychomotor development, epileptic encephalopathy, feeding difficulties, and hypotonia. This patient exhibited marked improvement of overall development following initiation of ketogenic diet at 31 months of age. To the best of our knowledge, this is the fourth case of functional PDC deficiency with a defined mutation in PDP1.

SYNOPSIS

Pyruvate dehydrogenase phosphatase (PDP) regulates pyruvate dehydrogenase complex (PDC) and defective PDP due to PDP1 mutations leads to PDC deficiency and congenital lactic acidosis.

Enzymatic testing sensitivity, variability and practical diagnostic algorithm for pyruvate dehydrogenase complex (PDC) deficiency

Pyruvate dehydrogenase complex (PDC) deficiency is a major cause of primary lactic acidemia in children. Prompt and correct diagnosis of PDC deficiency and differentiating between specific vs generalized, or secondary deficiencies has important implications for clinical management and therapeutic interventions. Both genetic and enzymatic testing approaches are being used in the diagnosis of PDC deficiency. However, the diagnostic efficacy of such testing approaches for individuals affected with PDC deficiency has not been systematically investigated in this disorder. We sought to evaluate the diagnostic sensitivity and variability of the various PDC enzyme assays in females and males at the Center for Inherited Disorders of Energy Metabolism (CIDEM). CIDEM data were filtered by lactic acidosis and functional PDC deficiency in at least one cell/tissue type (blood lymphocytes, cultured fibroblasts or skeletal muscle) identifying 186 subjects (51% male and 49% female), about half were genetically resolved with 78% of those determined to have a pathogenic PDHA1 mutation. Assaying PDC in cultured fibroblasts in cases where the underlying genetic etiology is PDHA1, was highly sensitive irrespective of gender; 97% (95% confidence interval [CI]: 90%-100%) and 91% (95% CI: 82%-100%) in females and males, respectively. In contrast to the fibroblast-based testing, the lymphocyte- and muscle-based testing were not sensitive (36% [95% CI: 11%-61%, p=0.0003] and 58% [95% CI: 30%-86%, p=0.014], respectively) for identifying known PDC deficient females with pathogenic PDHA1 mutations. In males with a known PDHA1 mutation, the sensitivity of the various cell/tissue assays (75% lymphocyte, 91% fibroblast and 88% muscle) were not statistically different, and the discordance frequency due to the specific cell/tissue used for assaying PDC was 0.15±0.11. Based on this data, a practical diagnostic algorithm is proposed accounting for current molecular approaches, enzyme testing sensitivity, and variability due to gender, cell/tissue type used for testing, and successive repeat testing.

Lethal neonatal case and review of primary short-chain enoyl-CoA hydratase (SCEH) deficiency associated with secondary lymphocyte pyruvate dehydrogenase complex (PDC) deficiency

Mutations in ECHS1 result in short-chain enoyl-CoA hydratase (SCEH) deficiency which mainly affects the catabolism of various amino acids, particularly valine. We describe a case compound heterozygous for ECHS1 mutations c.836T>C (novel) and c.8C>A identified by whole exome sequencing of proband and parents. SCEH deficiency was confirmed with very low SCEH activity in fibroblasts and nearly absent immunoreactivity of SCEH. The patient had a severe neonatal course with elevated blood and cerebrospinal fluid lactate and pyruvate concentrations, high plasma alanine and slightly low plasma cystine. 2-Methyl-2,3-dihydroxybutyric acid was markedly elevated as were metabolites of the three branched-chain α-ketoacids on urine organic acids analysis. These urine metabolites notably decreased when lactic acidosis decreased in blood. Lymphocyte pyruvate dehydrogenase complex (PDC) activity was deficient, but PDC and α-ketoglutarate dehydrogenase complex activities in cultured fibroblasts were normal. Oxidative phosphorylation analysis on intact digitonin-permeabilized fibroblasts was suggestive of slightly reduced PDC activity relative to control range in mitochondria. We reviewed 16 other cases with mutations in ECHS1 where PDC activity was also assayed in order to determine how common and generalized secondary PDC deficiency is associated with primary SCEH deficiency. For reasons that remain unexplained, we find that about half of cases with primary SCEH deficiency also exhibit secondary PDC deficiency. The patient died on day-of-life 39, prior to establishing his diagnosis, highlighting the importance of early and rapid neonatal diagnosis because of possible adverse effects of certain therapeutic interventions, such as administration of ketogenic diet, in this disorder. There is a need for better understanding of the pathogenic mechanisms and phenotypic variability in this relatively recently discovered disorder.

Succinyl-CoA synthetase (SUCLA2) deficiency in two siblings with impaired activity of other mitochondrial oxidative enzymes in skeletal muscle without mitochondrial DNA depletion

Mutations in SUCLA2 result in succinyl-CoA ligase (ATP-forming) or succinyl-CoA synthetase (ADP-forming) (A-SCS) deficiency, a mitochondrial tricarboxylic acid cycle disorder. The phenotype associated with this gene defect is largely encephalomyopathy. We describe two siblings compound heterozygous for SUCLA2 mutations, c.985A>G (p.M329V) and c.920C>T (p.A307V), with parents confirmed as carriers of each mutation. We developed a new LC-MS/MS based enzyme assay to demonstrate the decreased SCS activity in the siblings with this unique genotype. Both siblings shared bilateral progressive hearing loss, encephalopathy, global developmental delay, generalized myopathy, and dystonia with choreoathetosis. Prior to diagnosis and because of lactic acidosis and low activity of muscle pyruvate dehydrogenase complex (PDC), sibling 1 (S1) was placed on dichloroacetate, while sibling 2 (S2) was on a ketogenic diet. S1 developed severe cyclic vomiting refractory to therapy, while S2 developed Leigh syndrome, severe GI dysmotility, intermittent anemia, hypogammaglobulinemia and eventually succumbed to his disorder. The mitochondrial DNA contents in skeletal muscle (SM) were normal in both siblings. Pyruvate dehydrogenase complex, ketoglutarate dehydrogenase complex, and several mitochondrial electron transport chain (ETC) activities were low or at the low end of the reference range in frozen SM from S1 and/or S2. In contrast, activities of PDC, other mitochondrial enzymes of pyruvate metabolism, ETC and, integrated oxidative phosphorylation, in skin fibroblasts were not significantly impaired. Although we show that propionyl-CoA inhibits PDC, it does not appear to account for decreased PDC activity in SM. A better understanding of the mechanisms of phenotypic variability and the etiology for tissue-specific secondary deficiencies of mitochondrial enzymes of oxidative metabolism, and independently mitochondrial DNA depletion (common in other cases of A-SCS deficiency), is needed given the implications for control of lactic acidosis and possible clinical management.

Atenolol offers better protection than clonidine against cardiac injury in kainic acid-induced status epilepticus

BACKGROUND AND PURPOSE

Status epilepticus is increasingly associated with cardiac injury in both clinical and animal studies. The current study examined ECG activity for up to 48 h following kainic acid (KA) seizure induction and compared the potential of atenolol and clonidine to attenuate this cardiac pathology.

EXPERIMENTAL APPROACH

Sprague-Dawley rats (male, 300-350 g) were implanted with ECG and electrocorticogram electrodes to allow simultaneous telemetric recordings of cardiac and cortical responses during and after KA-induced seizures. Animals were randomized into saline controls, and saline vehicle-, clonidine- or atenolol-pretreated KA groups.

KEY RESULTS

KA administration in the saline-pretreated group produced an immediate bradycardic response (maximal decrease of 28 ± 6%), coinciding with low-level seizure activity. As high-level seizure behaviours and EEG spiking increased, tachycardia also developed, with a maximum heart rate increase of 38 ± 7% coinciding with QTc prolongation and T wave elevation. Both clonidine and atenolol pretreatment attenuated seizure activity and reduced KA-induced changes in heart rate, QTc interval and T wave amplitude observed during both bradycardic and tachycardic phases in saline-pretreated KA animals. Clonidine, however, failed to reduce the power of EEG frequencies. Atenolol and to a lesser extent clonidine attenuated the cardiac hypercontraction band necrosis, inflammatory infiltration, and oedema at 48 h after KA, relative to the saline-KA group.

CONCLUSIONS AND IMPLICATIONS

Severe seizure activity in this model was clearly associated with altered ECG activity and cardiac pathology. We suggest that modulation of sympathetic activity by atenolol provides a promising cardioprotective approach in status epilepticus.

Leukocyte telomere length in patients with schizophrenia: A meta-analysis

Schizophrenia has been suggested as a syndrome of accelerated aging. Telomere length (TL) decrease is considered one biological marker associated with age and can be accelerated by pathological characteristics present in schizophrenia. Several studies evaluated TL in schizophrenia, but the results are still controversial. The aim of this study was to conduct a meta-analysis of the existing results of TL in leukocytes of individuals with schizophrenia compared to healthy controls. A search was performed in PubMed, using the keywords 'telomere schizophrenia' and 'telomere psychosis'. We included data from original articles that measured TL in leukocytes of human patients with schizophrenia and healthy control subjects. 45 articles were found, but only 7 met our criteria. Telomere length of controls was not statistically different from that of patients with schizophrenia (p=0.07). Crossvalidation with the leave-one-out method resulted in a significant model (p=0.03) in which TL of individuals with schizophrenia is smaller than control (SMD=0.38; 95% CI=[0.05, 0.72]). We also propose a biological pathway through which schizophrenia could promote telomere erosion and how antipsychotics might compensate this loss. There are few studies made on this subject with diverse methodology and heterogeneous sample. Some articles did not consider other possible influences on TL. Overall our results suggest that TL is decreased in schizophrenia. Although this is consistent with the idea of accelerated aging, schizophrenia is a complex disease and there are several factors that influence TL that should be controlled in future studies.

Three rare diseases in one Sib pair: RAI1, PCK1, GRIN2B mutations associated with Smith-Magenis Syndrome, cytosolic PEPCK deficiency and NMDA receptor glutamate insensitivity

The National Institutes of Health Undiagnosed Diseases Program evaluates patients for whom no diagnosis has been discovered despite a comprehensive diagnostic workup. Failure to diagnose a condition may arise from the mutation of genes previously unassociated with disease. However, we hypothesized that this could also co-occur with multiple genetic disorders. Demonstrating a complex syndrome caused by multiple disorders, we report two siblings manifesting both similar and disparate signs and symptoms. They shared a history of episodes of hypoglycemia and lactic acidosis, but had differing exam findings and developmental courses. Clinical acumen and exome sequencing combined with biochemical and functional studies identified three genetic conditions. One sibling had Smith-Magenis Syndrome and a nonsense mutation in the RAI1 gene. The second sibling had a de novo mutation in GRIN2B, which resulted in markedly reduced glutamate potency of the encoded receptor. Both siblings had a protein-destabilizing homozygous mutation in PCK1, which encodes the cytosolic isoform of phosphoenolpyruvate carboxykinase (PEPCK-C). In summary, we present the first clinically-characterized mutation of PCK1 and demonstrate that complex medical disorders can represent the co-occurrence of multiple diseases.

Somatic mosaicism for a novel PDHA1 mutation in a male with severe pyruvate dehydrogenase complex deficiency

Pyruvate dehydrogenase complex (PDC) deficiencies are mostly due to mutations in the X-linked PDHA1 gene. Males with hemizygous PDHA1 mutations are clinically more severely affected, while those with mosaic PDHA1 mutations may manifest milder phenotypes. We report a patient harboring a novel, mosaic missense PDHA1 mutation, c.523G > A (p.A175T), with a severe clinical presentation of congenital microcephaly, significant brain abnormalities, persistent seizures, profound developmental delay, and failure to thrive. We review published cases of PDHA1 mosaicism.

Review of clinical trials for mitochondrial disorders: 1997-2012

Over the last 15 years, some 16 open and controlled clinical trials for potential treatments of mitochondrial diseases have been reported or are in progress, and are summarized and reviewed herein. These include trials of administering dichloroacetate (an activator of pyruvate dehydrogenase complex), arginine or citrulline (precursors of nitric oxide), coenzyme Q10 (CoQ10; part of the electron transport chain and an antioxidant), idebenone (a synthetic analogue of CoQ10), EPI-743 (a novel oral potent 2-electron redox cycling agent), creatine (a precursor of phosphocreatine), combined administration (of creatine, α-lipoate, and CoQ10), and exercise training (to increase muscle mitochondria). These trials have included patients with various mitochondrial disorders, a selected subcategory of mitochondrial disorders, or specific mitochondrial disorders (Leber hereditary optic neuropathy or mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes). The trial designs have varied from open-label/uncontrolled, open-label/controlled, or double-blind/placebo-controlled/crossover. Primary outcomes have ranged from single, clinically-relevant scores to multiple measures. Eight of these trials have been well-controlled, completed trials. Of these only 1 (treatment with creatine) showed a significant change in primary outcomes, but this was not reproduced in 2 subsequent trials with creatine with different patients. One trial (idebenone treatment of Leber hereditary optic neuropathy) did not show significant improvement in the primary outcome, but there was significant improvement in a subgroup of patients. Despite the paucity of benefits found so far, well-controlled clinical trials are essential building blocks in the continuing search for more effective treatment of mitochondrial disease, and current trials based on information gained from these prior experiences are in progress. Because of difficulties in recruiting sufficient mitochondrial disease patients and the relatively large expense of conducting such trials, advantageous strategies include crossover designs (where possible), multicenter collaboration, and the selection of very few, clinically relevant, primary outcomes.

Low-dose GYKI-52466: prophylactic preconditioning confers long-term neuroprotection and functional recovery following hypoxic-ischaemic brain injury

Experimental preconditioning provides beneficial outcomes in conditions such as cardiac surgery, brain surgery and stroke. Here we evaluated the protective effects of low-dose subcutaneous GYKI-52466 preconditioning in a rat model of hypoxic-ischaemic (HI) brain injury. Male Sprague-Dawley rats (postnatal day 26) were administered saline or GYKI-52466 (GYKI; 3-mg/kg, 90 min; 1-mg/kg, twice in 120 min; or 0.5-mg/kg, thrice in 180 min) prior to left common carotid artery occlusion. Animals were allowed to recover for 2h, and then placed in a hypoxia chamber (8% O₂/92% N₂; 33 ± 1°C) for 1h. A sham surgery group received saline without HI. Seizure activity was scored during hypoxia and sensorimotor tests performed before surgery and at 1, 7, 14 and 90 days post-HI. On days 14 and 90 brains were fixed and sectioned for the assessment of infarct size and ventricular enlargement. Low-dose GYKI-52466 preconditioning significantly reduced infarct volume and ventricular enlargement relative to saline-treated controls at day 14 after HI. On day 90, tissue loss was significantly reduced by GYKI 3-mg/kg compared to saline. Foot-faults, paw use asymmetry, and postural reflex scores were significantly improved in all GYKI treatment groups. Our results show that GYKI-52466 is effective at doses well-below, and at pre-administration intervals well-beyond previous studies, and suggest that a classical blockade of ionotropic AMPA receptors does not underlie its neuroprotective effects. Low-dose GYKI-52466 preconditioning represents a novel, prophylactic strategy for neuroprotection in a field almost devoid of effective pharmaceuticals.

Spectrum of neurological and survival outcomes in pyruvate dehydrogenase complex (PDC) deficiency: lack of correlation with genotype

Pyruvate dehydrogenase complex (PDC) deficiency is a relatively common mitochondrial disorder that primarily presents with neurological manifestations and lactic acidemia. We analyzed the clinical outcomes and neurological features of 59 consented symptomatic subjects (27 M, 32 F), who were confirmed to have PDC deficiency with defined mutations in one of the genes of PDC (PDHA1, n = 53; PDHB, n = 4; DLAT, n = 2), including 47 different mutations, of which 22 were novel, and for whom clinical records and/or structured interviews were obtained. 39% of these subjects (23/59) have died. Of these, 91% (21/23) died before age 4 years, 61% (14/23) before 1 year, and 43% (10/23) before 3 months. 56% of males died compared with 25% of females. Causes of death included severe lactic acidosis, respiratory failure, and infection. In subjects surviving past 6 months, a broad range of intellectual outcomes was observed. Of 42 subjects whose intellectual abilities were professionally evaluated, 19% had normal or borderline intellectual ability (CQ/IQ ≥ 70), 10% had mild intellectual disability (ID) (CQ/IQ 55-69), 17% had moderate ID (CQ/IQ 40-54), 24% had severe ID (CQ/IQ 25-39) and 33% had profound ID (CQ/IQ<25). Assessment by parents was comparable. Of 10 subjects who reached age 12 years, 9 had had professional IQ assessments, and only 4 had IQs ≥ 70 (only 2 of these 4 had assessments after age 12 years). The average outcome for females was severe-to-profound ID, whereas that of males was mild-to-moderate ID. Of subjects for whom specific neurological data were available, the majority had hypotonia (89%), and hypertonia or mixed hyper-/hypotonia (49%) were common. Seizures (57%), microcephaly (49%), and structural brain abnormalities including ventriculomegaly (67%) and agenesis, dysgenesis, or hypoplasia of the corpus callosum (55%) were common. Leigh syndrome was found in only 35%. Structural brain abnormalities were more common in females, and Leigh syndrome was more common in males. In a subgroup of 16 ambulatory subjects >3.5 years in whom balance was evaluated, ataxia was found in 13. Peripheral neuropathy was documented in 2 cases but not objectively evaluated in most subjects. Outcomes of this population with genetically confirmed PDC deficiency are heterogeneous and not distinctive. Correlations between specific genotypes and outcomes were not established. Although more females survive, related to the prevalence of X-linked PDHA1 mutations, symptomatic surviving females are generally more severely impaired cognitively and have a different pattern of neurological impairment compared to males. Neonatal or infant onset of symptoms was associated with poor outcomes. Males with PDHA1 mutations and low fibroblast PDC activity were less likely to survive beyond infancy. Recurrence rate in siblings of subjects with PDHA1 mutation was less than 5%. Paradoxically, in this retrospective review, potential factors considered possibly relevant to development, such as in vitro PDC activity, specific mutations, use of ketogenic diets, supplements, or medications, were generally not confirmed to be significantly correlated with objective outcomes of survival or neuro-cognitive function. Therefore, the basis of variability of these outcomes remains largely undetermined.

Design and implementation of the first randomized controlled trial of coenzyme CoQ₁₀ in children with primary mitochondrial diseases

We report the design and implementation of the first phase 3 trial of CoenzymeQ₁₀ (CoQ₁₀) in children with genetic mitochondrial diseases. A novel, rigorous set of eligibility criteria was established. The trial, which remains open to recruitment, continues to address multiple challenges to the recruitment of patients, including widely condoned empiric use of CoQ₁₀ by individuals with proven or suspected mitochondrial disease and skepticism among professional and lay mitochondrial disease communities about participating in placebo-controlled trials. These attitudes represent significant barriers to the ethical and scientific evaluation--and ultimate approval--of nutritional and pharmacological therapies for patients with life-threatening inborn errors of energy metabolism.

High prevalence of overweight and obesity in females with phenylketonuria

The primary treatment for phenylketonuria (PKU) is a low phenylalanine diet together with an amino acid-based, phenylalanine-free formula. Thus, PKU patients tend to consume a diet enriched in carbohydrates which could predispose to obesity. Studies in the 1980s and 1990s demonstrated that school-age phenylketonuria (PKU) patients have a higher mean body weight compared to a control population. However, no recent studies in the United States PKU population have examined whether this trend has persisted or whether adolescents are also affected. To investigate whether pediatric PKU populations (ages 2-20 years) in two major metropolitan areas of the United States (Cleveland, OH and Houston, TX) have a higher than expected percentage of overweight (BMI≥85th percentile) relative to the general population in the United States (NHANES), a retrospective chart review of PKU patients born between 1990 and 2008 and followed in Cleveland, OH (Rainbow Babies and Children's Hospital/University Hospitals Case Medical Center) and in Houston, TX (Texas Children's Hospital) was performed. Based on data from the U.S., 40% of pediatric PKU patients were overweight or obese. However, the percentage of overweight females (55%) and obese females (33%) is 1.8× and 2.1× higher respectively than expected based on comparison data from U.S. children. Further studies are necessary to identify potential strategies for prevention of excessive weight gain in children with PKU, especially in females.

Spectral analysis of electrocorticographic activity during pharmacological preconditioning and seizure induction by intrahippocampal domoic acid

Previously we have shown that low-dose domoic acid (DA) preconditioning produces tolerance to the behavioral effects of high-dose DA. In this study, we used electrocorticography (ECoG) to monitor subtle CNS changes during and after preconditioning. Young adult male Sprague-Dawley rats were implanted with a left cortical electrode, and acute recordings were obtained during preconditioning by contralateral intrahippocampal administration of either low-dose DA (15 pmoles) or saline, followed by a high-dose DA (100 pmoles) challenge. ECoG data were analyzed by fast Fourier transformation to obtain the percentage of baseline power spectral density (PSD) for delta to gamma frequencies (range: 1.25-100 Hz). Consistent with previous results, behavioral analysis confirmed that low-dose DA preconditioning 60 min before a high-dose DA challenge produced significant reductions in cumulative seizure scores and high level seizure behaviors. ECoG analysis revealed significant reductions in power spectral density across all frequency bands, and high-frequency/high-amplitude spiking in DA preconditioned animals, relative to saline controls. Significant correlations between seizure scores and ECoG power confirmed that behavioral analysis is a reliable marker for seizure analysis. The reduction of power in delta to gamma frequency bands in contralateral cortex does not allow a clear distinction between seizure initiation and seizure propagation, but does provide objective confirmation that pharmacological preconditioning by DA reduces network seizure activity.

In vivo seizure induction and affinity studies of domoic acid and isodomoic acids-D, -E and -F

Domoic acid and its isomers are produced via algal blooms and are found in high concentrations in shellfish. Here, we assessed the acute seizurogenic potencies of isomers-D, -E and -F and their binding affinities at heterogeneous populations of KA receptors from rat cerebrum. In addition, binding affinities of all six isomers (Iso-A through -F) were assessed at AMPA receptors. Radioligand displacement studies indicated that the seizurogenic potency of Iso-F (E-configuration) closely correlates with its affinities at both KA and AMPA receptors, whereas isomers-D (Z) and -E (E), which exhibit distinctly lower seizurogenic potencies, are quite weak displacers. Previously observed functional potencies for isomers-A, -B and -C (Sawant et al., 2008) correlated with AMPA receptor affinities observed here. Taken together, these findings call into question previous structure-activity rules. Significantly, in our hands, Iso-D was ten-fold less potent than Iso-F. To further explain observed links between structural conformation and functional potency, molecular modeling was employed. Modeling results closely matched the rank order of potency and binding data observed. We further assessed the efficacy of isomers-D, -E and -F as pharmacological preconditioning agents. Acute preconditioning with low-dose Iso-D, -E or -F, before high-dose DA failed to impart behavioural tolerance. This study has shed new light on structural conformations affecting non-NMDA ionotropic glutamate receptor binding and functional potency, and provides a foundation for future work in areas of AMPA and KA receptor modeling.

Deletion at chromosomal band Xp22.12-Xp22.13 involving PDHA1 in a patient with congenital lactic acidosis

We present a patient with congenital lactic acidosis, agenesis of the corpus callosum, and profound developmental delay. Assays of pyruvate dehydrogenase complex function were normal in lymphocytes, but decreased in fibroblasts. Sequencing of the PDHA1 gene did not reveal deleterious mutations, and BAC based microarray analysis did not reveal any chromosomal abnormality. However, gene dosage analysis with oligonucleotide-based chromosomal microarray revealed a deletion of Xp22.12-Xp22.13 involving complete deletion of PDHA1. This is the first report of a whole gene deletion of PDHA1 detected by oligonucleotide-based microarray.

Somatic mosaicism for PDHA1 mutation in a male with pyruvate dehydrogenase complex deficiency

Pyruvate dehydrogenase complex deficiency is a clinically heterogeneous disorder. Most cases are due to mutations in an X-linked PDHA1 gene encoding the E1alpha subunit of the multienzyme complex. Females with mutations in the PDHA1 gene may be asymptomatic or have a milder phenotype as a result of skewed X-inactivation, while males are typically more severely affected. We report a case of PDHA1 mosaicism in a male patient who had a milder phenotype.

Treatment of mitochondrial electron transport chain disorders: a review of clinical trials over the past decade

While many treatments for mitochondrial electron transport (respiratory) chain disorders have been suggested, relatively few have undergone controlled clinical trials. This review focuses on the recent history of clinical trials of dichloroacetate (DCA), arginine, coenzyme Q(10), idebenone, and exercise in both primary (congenital) disorders and secondary (degenerative) disorders. Despite prior clinical impressions that DCA had a positive effect on mitochondrial disorders, two trials of diverse subjects failed to demonstrate a clinically significant benefit, and a trial of DCA in MELAS found a major negative effect of neuropathy. Arginine also has been used to treat MELAS with promising effects, although a controlled trial is still needed for this potentially toxic agent. The anti-oxidant coenzyme Q(10) is very widely used for primary mitochondrial disorders but has not yet undergone a controlled clinical trial; such a trial is now underway, as well as trials of the co-Q analogue idebenone for MELAS and LHON. Greater experience has accumulated with multi-center trials of coenzyme Q(10) treatment to prevent the progression of Parkinson disease. Although initial smaller trials indicated a benefit, this has not yet been confirmed in subsequent trials with higher doses; a larger Phase III trial is now underway. Similarly, a series of trials of idebenone for Friedreich ataxia have shown some benefit in slowing the progression of cardiomyopathy, and controlled clinical trials are now underway to determine if there is significant neurological protection. Uncontrolled trials of exercise showed an increase of exercise tolerance in patients with disorders of mitochondrial DNA, but did not selectively increase the percentage of normal mtDNA; a larger partially controlled trial is now underway to evaluate this possible benefit. In summary, none of the controlled trials so far has conclusively shown a benefit of treatment with the agents tested, but some promising therapies are currently being evaluated in a controlled manner. These experiences underscore the importance of controlled clinical trials for evaluation of benefits and risks of recommended therapies. Application of such clinical trials to future more effective therapies for mitochondrial disorders will require multi-center collaboration, organization, leadership, and financial and advocacy support.

Establishing a consortium for the study of rare diseases: The Urea Cycle Disorders Consortium

The Urea Cycle Disorders Consortium (UCDC) was created as part of a larger network established by the National Institutes of Health to study rare diseases. This paper reviews the UCDC's accomplishments over the first 6years, including how the Consortium was developed and organized, clinical research studies initiated, and the importance of creating partnerships with patient advocacy groups, philanthropic foundations and biotech and pharmaceutical companies.

Infection-triggered familial or recurrent cases of acute necrotizing encephalopathy caused by mutations in a component of the nuclear pore, RANBP2

Acute necrotizing encephalopathy (ANE) is a rapidly progressive encephalopathy that can occur in otherwise healthy children after common viral infections such as influenza and parainfluenza. Most ANE is sporadic and nonrecurrent (isolated ANE). However, we identified a 7 Mb interval containing a susceptibility locus (ANE1) in a family segregating recurrent ANE as an incompletely penetrant, autosomal-dominant trait. We now report that all affected individuals and obligate carriers in this family are heterozygous for a missense mutation (c.1880C-->T, p.Thr585Met) in the gene encoding the nuclear pore protein Ran Binding Protein 2 (RANBP2). To determine whether this mutation is the susceptibility allele, we screened controls and other patients with ANE who are unrelated to the index family. Patients from 9 of 15 additional kindreds with familial or recurrent ANE had the identical mutation. It arose de novo in two families and independently in several other families. Two other patients with familial ANE had different RANBP2 missense mutations that altered conserved residues. None of the three RANBP2 missense mutations were found in 19 patients with isolated ANE or in unaffected controls. We conclude that missense mutations in RANBP2 are susceptibility alleles for familial and recurrent cases of ANE.

Cross-sectional multicenter study of patients with urea cycle disorders in the United States

Inherited urea cycle disorders comprise eight disorders (UCD), each caused by a deficiency of one of the proteins that is essential for ureagenesis. We report on a cross-sectional investigation to determine clinical and laboratory characteristics of patients with UCD in the United States. The data used for the analysis was collected at the time of enrollment of individuals with inherited UCD into a longitudinal observation study. The study has been conducted by the Urea Cycle Disorders Consortium within the Rare Diseases Clinical Research Network (RDCRN) funded by the National Institutes of Health. One-hundred eighty-three patients were enrolled into the study. Ornithine transcarbamylase (OTC) deficiency was the most frequent disorder (55%), followed by argininosuccinic aciduria (16%) and citrullinemia (14%). Seventy-nine percent of the participants were white (16% Latinos), and 6% were African American. Intellectual and developmental disabilities were reported in 39% with learning disabilities (35%) and half had abnormal neurological examination. Sixty-three percent were on a protein restricted diet, 37% were on Na-phenylbutyrate and 5% were on Na-benzoate. Forty-five percent of OTC deficient patients were on L-citrulline, while most patients with citrullinemia (58%) and argininosuccinic aciduria (79%) were on L-arginine. Plasma levels of branched-chain amino acids were reduced in patients treated with ammonia scavenger drugs. Plasma glutamine levels were higher in proximal UCD and in neonatal type disease. The RDCRN allows comprehensive analyses of rare inherited UCD, their frequencies and current medical practices.

Mutations of the E1beta subunit gene (PDHB) in four families with pyruvate dehydrogenase deficiency

Pyruvate dehydrogenase complex (PDC) deficiencies are a major cause of primary lactic acidosis. Most cases result from mutations of the gene for the pyruvate dehydrogenase E1alpha subunit (PDHA1), with fewer cases resulting from mutations in genes for E3, E3-binding protein, E2, and the E1beta subunit (PDHB). We have found four cases of PDHB mutations among 83 analyzed cases of PDC deficiency. In this series, PDHB mutations were found to be about 10% as frequent as PDHA1 mutations. All cases were diagnosed by low PDC activity, with normal E2 and E3 activities. These included a 6.5-year-old male (consanguineous, homozygous R36C); a neonatal female who died soon after birth, (compound heterozygous C306R/D319V), a 26-year-old female (heterozygous I142M/W165S), and a 13month old female (consanguineous, homozygous Y132C) who is a sibling of a previously published case. Their ethnic background is diverse (Caucasian, Arab, and African American descent). All cases had lactic acidosis and developmental delay. Three cases had agenesis of the corpus callosum, seizures, and hypotonia; one died within the first year of life. These clinical findings are similar to those of PDHA1 deficiency, except that ataxia was more frequent in PDHA1 cases and consanguinity was found only in PDHB families. PDC activity in lymphocytes from six parents is normal, who all are heterozygous carriers for the respective mutations. Immunoreactivity of E1beta was markedly reduced in one case and showed a slightly larger form of E1beta in one case. Computer analysis predicts that: R36C affects the interaction of several amino acids resulting in conformational change, C306R affects interaction of the two beta subunits, D319 is in the interface of E1 and E2, I142M affects conformation around a K ion affecting stability of the beta subunit, W165S affects hydrophobic interaction between the beta subunits, and Y132C affects interaction between the beta subunits. All of these residues are conserved in E1beta across species, and Y132 is also conserved in other TPP-requiring enzymes. These observations support the conclusion that these are pathogenic mutations.

Mutations in the MPV17 gene are responsible for rapidly progressive liver failure in infancy

MPV17 is a mitochondrial inner membrane protein of unknown function recently recognized as responsible for a mitochondrial DNA depletion syndrome. The aim of this study is to delineate the specific clinical, pathological, biochemical, and molecular features associated with mitochondrial DNA depletion due to MPV17 gene mutations. We report 4 cases from 3 ethnically diverse families with MPV17 mutations. Importantly, 2 of these cases presented with isolated liver failure during infancy without notable neurologic dysfunction.

CONCLUSION

We therefore propose that mutations in the MPV17 gene be considered in the course of evaluating the molecular etiology for isolated, rapidly progressive infantile hepatic failure.

Isodomoic acids A and C exhibit low KA receptor affinity and reduced in vitro potency relative to domoic acid in region CA1 of rat hippocampus

Several natural isomers of the seizurogenic neurotoxin domoic acid (DA) have been found to occur at up to mg/kg levels in shellfish. The aim of the current study was to assess the neurotoxic potency of isodomoic acids A and C (Iso-A and Iso-C), recently isolated from commercial shellfish. Hippocampal slices were obtained from young adult rats and maintained in a tissue recording chamber. Synaptically evoked population spikes were recorded in region CA1 before and after exposure to DA or its isomers. Both Iso-A and Iso-C produced transient neuronal hyperexcitability followed by a dose-dependent suppression of population spikes, but were, respectively, 4- and 20-fold less potent than DA (spike area: EC50 DA=237 nM; Iso-A=939 nM; Iso-C=4.6 microM). In the hippocampus, DA preconditioning induces tolerance to subsequent DA toxicity. However, in the present study neither Iso-A nor Iso-C were effective as preconditioning agents. Competitive binding studies using homomeric GluR6 kainate (kainic acid, KA) receptors showed the affinity of Iso-A to be 40-fold lower than DA (Ki DA=3.35 nM; Iso-A=130 nM). Together with earlier work showing Iso-C affinity at GluR6 receptors to be 240-fold lower than DA, our results suggest that neuroexcitatory effects of Iso-A in CA1 may involve both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and KA receptors, while Iso-C likely involves the activation of AMPA receptors alone.

A novel mutation in the mitochondrial tRNA(Ser(AGY)) gene associated with mitochondrial myopathy, encephalopathy, and complex I deficiency

PURPOSE

To identify molecular defects in a girl with clinical features of MELAS (mitochondrial encephalomyopathy and lactic acidosis) and MERRF (ragged-red fibres) syndromes.

METHODS

The enzyme complex activities of the mitochondrial respiratory chain were assayed. Temporal temperature gradient gel electrophoresis was used to scan the entire mitochondrial genome for unknown mitochondrial DNA (mtDNA) alterations, which were then identified by direct DNA sequencing.

RESULTS

A novel heteroplasmic mtDNA mutation, G12207A, in the tRNA(Ser(AGY)) gene was identified in the patient who had a history of developmental delay, feeding difficulty, lesions within her basal ganglia, cerebral atrophy, proximal muscle weakness, increased blood lactate, liver dysfunction, and fatty infiltration of her muscle. Muscle biopsy revealed ragged red fibres and pleomorphic mitochondria. Study of skeletal muscle mitochondria revealed complex I deficiency associated with mitochondrial proliferation. Real time quantitative PCR analysis showed elevated mtDNA content, 2.5 times higher than normal. The tRNA(Ser(AGY)) mutation was found in heteroplasmic state (92%) in the patient's skeletal muscle. It was not present in her unaffected mother's blood or in 200 healthy controls. This mutation occurs at the first nucleotide of the 5' end of tRNA, which is involved in the formation of the stem region of the amino acid acceptor arm. Mutation at this position may affect processing of the precursor RNA, the stability and amino acid charging efficiency of the tRNA, and overall efficiency of protein translation.

CONCLUSION

This case underscores the importance of comprehensive mutational analysis of the entire mitochondrial genome when a mtDNA defect is strongly suggested.

A nonsense mutation of PEPD in four Amish children with prolidase deficiency

Encoded by the peptidase D (PEPD) gene located at 19q12-q13.11, prolidase is a ubiquitous cytosolic enzyme that catalyzes hydrolysis of oligopeptides with a C-terminal proline or hydroxyproline. We describe here four Amish children with a severe phenotype of prolidase deficiency in the Geauga settlements of Ohio as the first report of prolidase deficiency in the Amish population as well as in the United States. The patients presented with infection, hepatosplenomegaly, or thrombocytopenia, in contrast to most cases previously reported in the literature, presenting with skin ulcers. All four patients had typical facial features, classic skin ulcers, and multisystem involvement. Recurrent infections, asthma-like chronic reactive airway disease, hyperimmunoglobulins, hepatosplenomegaly with mildly elevated aspartate transaminase (AST), anemia, and thrombocytopenia were common and massive imidodipeptiduria was universal. Prolidase activity in our patients is nearly undetectable. Direct sequencing of PCR-amplified genomic DNA for all of the exons from the four patients revealed the same homozygous single nucleotide mutation c.793 T > C in exon 11, resulting in a premature stop-codon at amino acid residue 265 (p.R265X). It is speculated that the severe phenotype in these patients might be associated with the type of the PEPD gene mutation.

Controlled clinical trial of dichloroacetate for treatment of congenital lactic acidosis in children

OBJECTIVE

Open-label studies indicate that oral dichloroacetate (DCA) may be effective in treating patients with congenital lactic acidosis. We tested this hypothesis by conducting the first double-blind, randomized, control trial of DCA in this disease.

METHODS

Forty-three patients who ranged in age from 0.9 to 19 years were enrolled. All patients had persistent or intermittent hyperlactatemia, and most had severe psychomotor delay. Eleven patients had pyruvate dehydrogenase deficiency, 25 patients had 1 or more defects in enzymes of the respiratory chain, and 7 patients had a mutation in mitochondrial DNA. Patients were preconditioned on placebo for 6 months and then were randomly assigned to receive an additional 6 months of placebo or DCA, at a dose of 12.5 mg/kg every 12 hours. The primary outcome results were (1) a Global Assessment of Treatment Efficacy, which incorporated tests of neuromuscular and behavioral function and quality of life; (2) linear growth; (3) blood lactate concentration in the fasted state and after a carbohydrate meal; (4) frequency and severity of intercurrent illnesses and hospitalizations; and (5) safety, including tests of liver and peripheral nerve function.

OUTCOME

There were no significant differences in Global Assessment of Treatment Efficacy scores, linear growth, or the frequency or severity of intercurrent illnesses. DCA significantly decreased the rise in blood lactate caused by carbohydrate feeding. Chronic DCA administration was associated with a fall in plasma clearance of the drug and with a rise in the urinary excretion of the tyrosine catabolite maleylacetone and the heme precursor delta-aminolevulinate.

CONCLUSIONS

In this highly heterogeneous population of children with congenital lactic acidosis, oral DCA for 6 months was well tolerated and blunted the postprandial increase in circulating lactate. However, it did not improve neurologic or other measures of clinical outcome.

Somatic mosaicism in a male with an exon skipping mutation in PDHA1 of the pyruvate dehydrogenase complex results in a milder phenotype

Pyruvate dehydrogenase complex (PDC) deficiency is commonly due to mutations of PDHA1 on the X chromosome. Milder phenotypic manifestations occur in heterozygous females than in hemizygous males with the same mutation, and females are more likely to survive with severe mutations. The boy described here had hypotonia, moderate developmental delay, tremors, normal growth and brain MRI, and normal to slightly elevated lactate. PDC activity was low in skin fibroblasts and skeletal muscle (27-37%) but normal in lymphocytes. PDHA1 cDNA from cultured fibroblasts revealed two populations, one normal, the other lacking exon 6 (c.511-603 del). Genomic DNA from fibroblasts contained both normal and mutant (g.592G-->A) sequences within exon 6. Expression of minigene constructs containing exons 5, 6, and 7 with or without this mutation in 293T cells confirmed that the mutation alters splicing of exon 6. The mutant to wild-type DNA ratio varied substantially across tissues. Immunoblotting of fibroblast lysates detected only wild-type E1alpha protein. Immunocytochemistry of cultured skin fibroblasts showed a mosaic pattern with 60% of cells positive for E1alpha and 40% negative, consistent with PDC activity and DNA analysis. Karyotyping, FISH analyses, and genotyping revealed a 46XY male without chimerism. These data indicate somatic mosaicism for a mutation within exon 6 that causes exon skipping and production of a non-functional protein. The mutated 592G residue is conserved among all eukaryotes. Substituting A for G apparently alters normal splicing by creating a SRp40 exonic splice enhancer site. The milder phenotype in this male is accounted for by the mixture of normal cells and cells lacking E1alpha. Immunocytochemistry was a useful adjunct to molecular analysis for demonstrating mosaicism.

Oxidative phosphorylation analysis: assessing the integrated functional activity of human skeletal muscle mitochondria--case studies

Oxidative phosphorylation analysis, performed on freshly-isolated mitochondria, assesses the integrated function of the electron transport chain (ETC) coupled to ATP synthesis, membrane transport, dehydrogenase activities, and the structural integrity of the mitochondria. In this review, a case study approach is employed to highlight detection of defects in the adenine nucleotide translocator, the pyruvate dehydrogenase complex, fumarase, coenzyme Q function, fatty acid metabolism, and mitochondrial membrane integrity. Our approach uses the substrates glutamate, pyruvate, 2-ketoglutarate (coupled with malonate), malate, and fatty acid substrates (palmitoylcarnitine, octanoylcarnitine, palmitoyl-CoA (with carnitine), octanoyl-CoA (with carnitine), octanoate and acetylcarnitine) in addition to succinate, durohydroquinone and TMPD/ascorbate to uncover metabolic defects that would not be apparent from ETC assays performed on detergent-solubilized mitochondria.

Client-centred assessment and the identification of meaningful treatment goals for individuals with a spinal cord injury

STUDY DESIGN

Retrospective analysis.

OBJECTIVES

(1) Describe the self-care, productivity and leisure problems identified by individuals with a spinal cord injury (SCI) during rehabilitation, (2) describe the perceived level of satisfaction and performance with self-care, productivity and leisure activities following an SCI, (3) quantify the relationship between the Canadian occupational performance measure (COPM), a client-centred, individualized measure of function, and the functional independence measure (FIM).

SETTING

Tertiary rehabilitation centre, spinal cord injury unit, GF Strong Rehabilitation Centre, Vancouver, Canada.

METHODS

Health records from 41 individuals with an SCI admitted between 2000 and 2002 were reviewed. Information was obtained from assessments performed on admission and discharge. Self-care, productivity and leisure problems identified by individuals with an SCI were described and their perceived level of performance and satisfaction was calculated. The relationship between the COPM and the FIM was measured by the Pearson product correlation.

RESULTS

Self-care goals were identified most frequently (79%) followed by productivity (12%) and leisure (9%) goals. The top three problems identified by individuals with an SCI were functional mobility (including transfers and wheelchair use), dressing and grooming. A fair relationship was found between the COPM and the FIM (r between 0.351 and 0.514, P<0.05).

CONCLUSIONS

The results highlight the importance of including a client-centred outcome measure in the assessment of individuals with an SCI. Initial support is provided for use of the COPM in individuals with an SCI.

Comparison of the in vitro and in vivo neurotoxicity of three new sources of kainic acid

Historically, all commercially available kainic acid has been derived from a single biological source using a consistent method of extraction and purification. That source became unavailable in 1995. Recently, three new commercial suppliers of kainic acid have made the product available, but the source of the material and the purification processes used differ. Our objective was to systematically compare the response produced by each of these new sources of kainic acid using three established neurobiological techniques: neuronal cell culture, hippocampal slice electrophysiology, and whole animal behavioural toxicity. Results in all three systems indicated no overall differences between the three formulations, although studies in both cerebellar neuron cultures and whole animal toxicity testing in mice, revealed some significant differences that may imply subtle differences in receptor selectivity and/or potency. We conclude that all three sources of kainic acid are viable alternatives to traditional kainate but they may not be identical. Until further information becomes available researchers may want to avoid using the three formulations interchangeably, and take note of the source of kainic acid when evaluating literature describing results from other laboratories.

Autosomal dominant acute necrotizing encephalopathy maps to 2q12.1-2q13

In autosomal dominant acute necrotizing encephalopathy (ADANE), apparently healthy children develop necrotizing lesions in their thalami and brainstems in the course of febrile illnesses. We used DNA from affected subjects and obligate carriers to map ADANE to a 6.5Mb region on chromosome 2. Sequencing of four candidate genes in the interval (BCL2L11, ST6GalII, CHT1, and FLJ20019), involved in apoptosis, viral recognition, choline transport, and electron transport, showed no disease causing mutations.

Autosomal dominant acute necrotizing encephalopathy

OBJECTIVE

To define the clinical and biochemical abnormalities of an autosomal dominant form of acute encephalopathy.

METHODS

The clinical details of 11 affected family members in comparison with 63 unaffected relatives were analyzed.

RESULTS

Affected children become comatose after onset of a febrile illness. Outcomes include full recovery, permanent neurologic impairment, and death. Recurrences produce more severe impairments. Lesions of necrotizing encephalopathy of the thalamus and brainstem are present on autopsy and MRI. Oxidative phosphorylation of intact mitochondria from a muscle biopsy shows loose coupling. Unaffected family members, including obligate carriers, share no clinical characteristics, demonstrating incomplete penetrance.

CONCLUSIONS

Characteristic pathology and MRI findings define this disorder of autosomal dominant acute encephalopathy. Leigh syndrome and sporadic acute necrotizing encephalopathy share similarities but are distinct.

AMPA/kainate and group-I metabotropic receptor antagonists infused into different brain areas impair memory formation of inhibitory avoidance in rats

Several lines of evidence suggest that glutamate receptors are involved in memory processing. To examine the role of non-N-methyl-D-aspartate (non-NMDA) glutamate receptors on memory consolidation, rats were bilaterally implanted with cannulae aimed at the CA1 region of the dorsal hippocampus (CA1), entorhinal cortex (ENTO), posterior parietal cortex (PPC) or the basolateral nucleus of the amygdala (BLA), and trained in a one-trial step-down inhibitory avoidance task. At different times after training, the alpha-amino 3-hydroxy-5 methyl 4-isoxazole propionate (AMPA) receptor blocker, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (1.0 microg/side), or the metabotropic type-I receptor antagonist, 2-amino-3-phosphonopropionic acid (AP3) (1.0 microg/side), were infused into the above-mentioned structures. CNQX produced retrograde amnesia when infused into BLA or CA1 0, 30, 90 or 180 min post-training but not at later times. AP3 blocked memory consolidation when administered into CA1 0, 30 or 180 min post-training, while in BLA, it was amnestic only when given 0 or 30 min after the training session. CNQX and AP3 had no effect on memory when administered into ENTO or PPC at any time. Our data suggest that the consolidation of the avoidance memory requires intact non-NMDA receptor function in the hippocampus and the basolateral nucleus of the amygdala, but not necessarily in the entorhinal and parietal cortex, for long periods after training.

Gene therapy for pyruvate dehydrogenase E1alpha deficiency using recombinant adeno-associated virus 2 (rAAV2) vectors

To determine the feasibility of gene transfer to correct defects in the E1alpha subunit of the pyruvate dehydrogenase (PDH) complex (PDC), we constructed rAAV vectors that expressed PDH E1alpha, either alone or with a green fluorescent protein tag, from a hybrid cytomegalovirus (CMV) enhancer/chicken beta-actin (CB) promoter. These vectors were functional in vitro, as judged by increased expression of mRNA in vector-transduced deficient cell lines and correction of the biochemical defect in PDH activity in these cells. Approximately 30% of wild-type levels of PDH activity were restored under conditions with which only about 15% of cells were transduced. These same vectors were then used in vivo to transduce neurons within the rat striatum. Gene transfer, expression, and translocation into mitochondria were observed, without any obvious untoward effects. In vivo vector-mediated PDH expression persisted for at least 1 year after injection, indicating the stability of gene transfer. These studies provide the basis for future efforts to develop a recombinant AAV (rAAV)-based gene therapy approach for the correction of PDC deficiency.

Domoic acid-induced hippocampal CA1 hyperexcitability independent of region CA3 activity

Domoic acid (DOM) is a potent agonist of AMPA and kainic acid (KA) receptors in the CNS and is known to produce seizures acutely, and lasting excitotoxic damage in several brain regions. While the excitotoxic effects of DOM are well documented, its seizurogenic properties are less clear. In this study, we assessed the acute effects of DOM and KA in region CA1 of intact rat hippocampal slices (CA3-on) and in slices lacking region CA3 (CA3-off). Orthodromic Schaffer collateral-evoked CA1 field potentials (population spikes and somal EPSP's) were monitored during DOM and KA (10-500 nM) administration. In CA3-off slices both KA and DOM produced immediate increases in CA1 population spike amplitude. With prolonged exposure, lasting dose-dependent reductions in spike amplitude and EPSP slope were observed, possibly due to depolarising conduction block following excessive AMPA/KA receptor activation; DOM was several-fold more potent than KA in this regard. Population spike threshold did not vary with DOM, but in CA3-on slices a dose-dependent steepening of the I/O curve and increase in maximum spike amplitude was seen. CA1 hyperexcitability, as evidenced by the appearance of prominent second and third population spikes, was equivalently increased across a range of DOM concentrations in both CA3-on and CA3-off slices and, in general, DOM-induced CA1 hyperexcitability was not enhanced by the presence of CA3 for any of the other variables assessed in this study. These findings show that DOM directly promotes neuronal hyperactivity in region CA1, presumably due to tonic AMPA and/or KA-receptor mediated depolarization, and further suggests that DOM-induced hyperactivity in the recurrently networked, AMPA/KA-receptor rich region CA3 does not contribute to the onset and spread of limbic seizures during relatively mild DOM intoxication.

NOESY on neurotoxins: NMR and conformational assignments of picrotoxins

Nuclear Overhauser effect spectroscopy (NOESY) gave full assignments of the 1H-NMR spectra of the picrotoxane neurotoxins tutin, hyenanchin, picrotoxinin and picrotin, as well as the solution conformations of these compounds, consistent with molecular modelling. Fully assigned 13C-NMR data are reported.

Mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1) in patients with a pyruvate dehydrogenase complex deficiency

Defects in the pyruvate dehydrogenase (PDH) complex are an important cause of primary lactic acidosis, a frequent manifestation of metabolic disease in children. Clinical symptoms can vary considerably in patients with PDH complex deficiencies, and almost equal numbers of affected males and females have been identified, suggesting an autosomal recessive mode of inheritance of the disease. However, the great majority of PDH complex deficiencies result from mutations in the X-linked pyruvate dehydrogenase (E1) alpha subunit gene (PDHA1). The major factors that contribute to the clinical variation in E1alpha deficiency and its resemblance to a recessive disease are developmental lethality in some males with severe mutations and the pattern of X-inactivation in females. To date, 37 different missense/nonsense and 39 different insertion/deletion mutations have been identified in the E1alpha subunit gene of 130 patients (61 females and 69 males) from 123 unrelated families. Insertion/deletion mutations occur preferentially in exons 10 and 11, while missense/nonsense mutations are found in all exons. In males, the majority of missense/nonsense mutations are found in exons 3, 7, 8 and 11, and three recurrent mutations at codons R72, R263 and R378 account for half of these patients with missense/nonsense mutations (25 of 50). A significantly lower number of females is found with missense/nonsense mutations (25). However, 36 females out of 55 affected patients have insertion/deletion mutations. The total number of female and male patients is thus almost the same, although a difference in the distribution of the type of mutations is evident between both sexes. In many families, the parents of the affected patients were studied for the presence of the PDHA1 mutation. The mutation was never present in the somatic cells of the father; in 63 mothers studied, 16 were carriers (25%). In four families, the origin of the new mutation was determined to be twice paternal and twice maternal.

A neurophysiological method of rapid detection and analysis of marine algal toxins

We have examined the effectiveness of the in vitro rat hippocampal slice preparation as a means of rapidly and specifically detecting the marine algal toxins saxitoxin, brevetoxin, and domoic acid and have identified toxin-specific electrophysiological signatures for each. Brevetoxin (PbTX3, 50-200 nM) produced a significant reduction in orthodromic population spike amplitude which was quick to reverse during a 50 min wash-out, while antidromic population spikes and field EPSPs exhibited only slight reductions, and fibre spiof orthodrokes showed no change at all. Domoic acid (100 nM) produced a robust, reversible increase in amplitude mic spikes, and the appearance of multiple spikes (i.e., epileptiform activity) within minutes of toxin wash-in. Other notable features of the domoic acid signature included a significant decrease in amplitude of the field EPSPs, and a complete absence of effect on either antidromic or fibre spikes. Fifty nanomolar saxitoxin (PSP) abolished all responses in all slices. Only antidromic spikes showed any recovery during wash-out. Field EPSP and fiber spike analysis further demonstrated that the preparation is capable of reliably detecting saxitoxin in a linearly responsive fashion at toxin concentrations of 25-200 nM, and tests of naturally contaminated shellfish confirmed the utility of this assay as a screening method for PSP. Our findings suggest that the in vitro hippocampal slice preparation has potential in the detection and analysis of three marine algal toxins important to the shellfish industry.

High-affinity [3H] kainic acid binding to brain membranes: a re-evaluation of ligand potency and selectivity

[3H]Kainic acid ([3H]KA) is a widely used tool for studying the KA class of excitatory amino acid receptors. [3H]KA of significantly higher specific activity has become available permitting use of radioligand concentrations below the dissociation constant (K(D)) of the high-affinity binding site. We employed low radioligand (0.05-0.2 nM) and receptor concentrations (0.01 nM) to gain new insights into the binding characteristics of the high-affinity KA binding site in a standard preparation of lyzed synaptosomal membranes from the cerebral cortex of male Sprague-Dawley rats. Under these conditions, KA binds to a single class of high-affinity sites with a K(D) of 1.0+/- 0.3 nM. The potencies of competing agents are considerably higher than published reports. Specifically, domoic acid, glutamate, and glutamine exhibit IC(50) values for displacing [3H]KA of 0.37+/-0.02, 94+/-13, and 1500+/-500 nM, respectively. Domoate (1 microM) was tested against a panel of 32 central nervous system binding sites and found to be inactive at each, indicating this toxin displays considerable selectivity. This study illustrates the remarkable potency of domoic acid and underlines the importance of performing radioligand binding studies at concentrations of constituents that permit characterization of high-affinity interactions.

Characterization of the regulatory region of the human testis-specific form of the pyruvate dehydrogenase alpha-subunit (PDHA-2) gene

The alpha-subunit of human pyruvate dehydrogenase (E(1)) is encoded by two separate genes. The gene located on chromosome X (PDHA-1) is expressed in somatic tissues, whereas the second gene (PDHA-2), located on chromosome 4, is expressed only in post-meiotic spermatogenic cells. A genomic fragment harboring the human gene encoding PDHA-2 has been isolated and approximately 800 nucleotides of the promoter region have been characterized. Functional studies of the promoter indicate the presence of both enhancer and repressor elements that are common to other genes that are only expressed in mature sperm.

Molecular characterization of pyruvate carboxylase deficiency in two consanguineous families

Pyruvate carboxylase (PC) is a biotinylated mitochondrial enzyme that catalyzes the conversion of pyruvate to oxaloacetate. Children with inborn errors of PC metabolism have lactic acidosis, hypoglycemia, and mental retardation. The variable severity of the clinical phenotype is dependent on both genetic and environmental factors. Two consanguineous families with moderate forms of PC deficiency were characterized at the biochemical and molecular levels. In both families, the probands were found to have low PC activity (range, 2-25% of control) in blood lymphocytes and skin fibroblasts associated with either diminished or normal protein levels. In the first case, sequencing of patient-specific PC cDNA demonstrated a T to C substitution at nucleotide 434, which causes a valine to alanine change at amino acid residue 145. Direct sequencing of the parents showed that they are heterozygous for this mutation. In the second family, a brother and sister had mental retardation and episodes of severe lactic/ketoacidosis in early childhood. In these cases, a C to T substitution at nucleotide 1351 results in a cysteine for arginine substitution at amino acid residue 451; the parents were also found to be heterozygous for this mutation. In both families, no other mutations were found, and both substitutions occurred in relatively conserved amino acid residues. These mutations, located in the biotin carboxylase domain, provide a unique opportunity to analyze how natural occurring mutations affect PC function.

Primary hypothyroidism mimicking a pituitary macroadenoma

Pituitary macroadenomas occur infrequently in children and can present with visual dysfunction or endocrinopathy. Occasionally, primary end-organ failure can cause reactive enlargement of the pituitary gland that may be clinically and radiographically indistinguishable from pituitary macroadenoma. The authors describe an example of reactive pituitary hyperplasia from primary hypothyroidism that mimicked a pituitary macroadenoma in a child. Recognition of this entity, which responds to medical therapy, is important because it can spare patients unnecessary surgery.

Deficiency of dihydrolipoamide dehydrogenase due to two mutant alleles (E340K and G101del). Analysis of a family and prenatal testing

A male child with metabolic acidosis was diagnosed as having dihydrolipoamide dehydrogenase (E3) deficiency. E3 activity of the proband's cultured fibroblasts and blood lymphocytes was 3-9% of normal, while in the parent's lymphocytes it was about 60% of normal. The proband's pyruvate dehydrogenase complex (PDC) and the alpha-ketoglutarate dehydrogenase complex activities from cultured skin fibroblasts were 12% and 6% of normal, respectively. PDC activity in the parents cultured fibroblasts was 25-31% of normal. Western and Northern blot analyses showed similar quantities of E3 protein and mRNA in cultured fibroblasts from the proband and his parents. DNA sequencing of cloned full-length E3 cDNAs, from the proband and the parents, showed two mutations on different alleles of proband were inherited from the parents. One mutation is a three nucleotide (AGG) deletion, from the mother, resulting in deletion of Gly101 in the FAD binding domain. The other mutation is a nucleotide substitution (G to A), from the father, leading to substitution of Lys for Glu340 in the central domain. The same deletion mutation was found in E3 cDNA from a chorionic villus sample and cultured fibroblasts obtained from the mother's subsequent offspring. This finding illustrates the possibility of successful prenatal diagnosis of E3 deficiency utilizing mutations characterized prior to initiation of pregnancy.