Objective
Voltage‐gated sodium (Na+) channels underlie action potential generation and propagation and hence are central to the regulation of excitability in the nervous system. Mutations in the ...genes SCN1A, SCN2A, and SCN8A, encoding the Na+ channel pore‐forming (α) subunits Nav1.1, 1.2, and 1.6, respectively, and SCN1B, encoding the accessory subunit β1, are established causes of genetic epilepsies. SCN3A, encoding Nav1.3, is known to be highly expressed in brain, but has not previously been linked to early infantile epileptic encephalopathy. Here, we describe a cohort of 4 patients with epileptic encephalopathy and heterozygous de novo missense variants in SCN3A (p.Ile875Thr in 2 cases, p.Pro1333Leu, and p.Val1769Ala).
Methods
All patients presented with treatment‐resistant epilepsy in the first year of life, severe to profound intellectual disability, and in 2 cases (both with the variant p.Ile875Thr), diffuse polymicrogyria.
Results
Electrophysiological recordings of mutant channels revealed prominent gain of channel function, with a markedly increased amplitude of the slowly inactivating current component, and for 2 of 3 mutants (p.Ile875Thr and p.Pro1333Leu), a leftward shift in the voltage dependence of activation to more hyperpolarized potentials. Gain of function was not observed for Nav1.3 variants known or presumed to be inherited (p.Arg1642Cys and p.Lys1799Gln). The antiseizure medications phenytoin and lacosamide selectively blocked slowly inactivating over transient current in wild‐type and mutant Nav1.3 channels.
Interpretation
These findings establish SCN3A as a new gene for infantile epileptic encephalopathy and suggest a potential pharmacologic intervention. These findings also reinforce the role of Nav1.3 as an important regulator of neuronal excitability in the developing brain, while providing additional insight into mechanisms of slow inactivation of Nav1.3. Ann Neurol 2018;83:703–717
Abstract Background We identified a group of patients with ATP1A3 mutations at residue 756 who display a new phenotype, distinct from alternating hemiplegia of childhood, rapid-onset ...dystonia-parkinsonism, and cerebellar ataxia, areflexia, pes cavus, optic atrophy, sensorineural hearing loss syndromes. Methods Four patients with c.2267G>A (R756H) mutations from two families and two patients with c.2267G>T (R756L) mutations from one family are described and compared with the previously reported patients with mutations resulting in R756H and R756C protein variants. Results Patients with ATP1A3 R756H have onset in childhood of infrequent, fever-triggered paroxysms of encephalopathy and weakness with slowly improving but persistent deficits. Motor findings of weakness are mostly generalized, and patients may also have bulbar or oculomotor problems. Longer-term outcomes range from mild motor apraxia with near-normal function to persistent dysphagia, dysarthria, cognitive deficit, motor apraxia, and inability to walk because of ataxia. Patients with ATP1A3 R756L have a similar phenotype that includes paroxysmal, stepwise progression of ataxia associated with infections. Conclusions ATP1A3 mutations affecting residue 756 result in a clinical syndrome, separate from those associated with previously described ATP1A3 mutations, which consists chiefly of fever-induced paroxysmal weakness and encephalopathy (FIPWE). Patients with R756L and R756C protein variants display more prominent ataxia, overlapping with the relapsing encephalopathy with cerebellar ataxia syndrome previously described in a patient with the c.2266C>T (R756C) mutation. All patients reported with mutations at residue 756 to date have had a similar episodic course and clinical features. Patients with mutations of ATP1A3 residue 756 appear to have a distinct clinical phenotype compared with patients with other ATP1A3 mutations, with fever-induced encephalopathy as key differentiating feature.
The term "senile chorea" was previously used to describe cases of insidious onset chorea in elderly patients who lacked family history of chorea. However, many of these patients have an identifiable ...etiology for their chorea. In this article, we discuss a case of generalized, insidious onset chorea in an 89-year-old man and apply a systematic diagnostic approach to chorea in the elderly to arrive at a diagnosis of late-onset Huntington's disease. He is to our knowledge the second oldest case of late-onset Huntington's disease reported in the literature and his case lends support to the expanding phenotype of Huntington's disease.
Objective
Rett syndrome (RTT) and epileptic encephalopathy (EE) are devastating neurodevelopmental disorders with distinct diagnostic criteria. However, highly heterogeneous and overlapping clinical ...features often allocate patients into the boundary of the two conditions, complicating accurate diagnosis and appropriate medical interventions. Therefore, we investigated the specific molecular mechanism that allows an understanding of the pathogenesis and relationship of these two conditions.
Methods
We screened novel genetic factors from 34 RTT‐like patients without MECP2 mutations, which account for ∼90% of RTT cases, by whole‐exome sequencing. The biological function of the discovered variants was assessed in cell culture and Xenopus tropicalis models.
Results
We identified a recurring de novo variant in GABAB receptor R2 (GABBR2) that reduces the receptor function, whereas different GABBR2 variants in EE patients possess a more profound effect in reducing receptor activity and are more responsive to agonist rescue in an animal model.
Interpretation
GABBR2 is a genetic factor that determines RTT‐ or EE‐like phenotype expression depending on the variant positions. GABBR2‐mediated γ‐aminobutyric acid signaling is a crucial factor in determining the severity and nature of neurodevelopmental phenotypes. Ann Neurol 2017;82:466–478
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 4years, 61% (14/23) before 1year, and 43% (10/23) before 3months. 56% of males died compared with 25% of females. Causes of death included severe lactic acidosis, respiratory failure, and infection. In subjects surviving past 6months, 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 12years, 9 had had professional IQ assessments, and only 4 had IQs≥70 (only 2 of these 4 had assessments after age 12years). 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 >3.5years 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.
► 59 PDC-deficient subjects had 47 mutations of PDHA1 (53 cases), PDHB, and DLAT. ► No pathogenic mutations were found in 33 (36%) of PDC deficient subjects. ► Mortality was greatest in first 4years and in males (56%) vs. females (25%). ► Female survivors had lower cognitive function and more brain malformations. ► Male survivors had higher frequency of Leigh syndrome.
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.
•We describe a case compound heterozygous for ECHS1 mutations c.836T>C (novel) and c.8C>A identified by whole exome sequencing. SCEH deficiency was confirmed with very low SCEH activity in fibroblasts and nearly absent immunoreactivity of SCEH.•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 and we find that about half of cases with primary SCEH deficiency also exhibit secondary PDC deficiency.•This case highlights 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.
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.
•We describe two siblings compound heterozygous for SUCLA2 mutations, c.985A>G (p.M329V) and c.920C>T (p.A307V).•We developed a new LC-MS/MS-based assay to quantify succinyl-CoA synthetase enzyme activity.•We describe for the first time secondary pyruvate dehydrogenase complex deficiency in two siblings with SUCLA2 gene defects.
Young onset dementias present significant diagnostic challenges. We present the case of a 35-year-old Kuwaiti man with social withdrawal, drowsiness, irritability, anxiety, aphasia, memory loss, ...hypereflexia, and Parkinsonism. Brain MRI showed bilateral symmetric gradient echo hypointensities in the globi pallidi and substantiae nigrae. Left cortical hypometabolism was seen on brain fluorodeoxyglucose positron emission tomography. A cortical brain biopsy revealed a high Lewy body burden. Genetic testing revealed a homozygous p.T11M mutation in the C19orf12 gene consistent with mitochondrial membrane protein-associated neurodegeneration. This is the oldest onset age of MPAN reported.
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