SUMMARYThe first mutations identified in SLC2A1, encoding the glucose transporter type 1 (GLUT1) protein of the blood-brain barrier, were associated with severe epileptic encephalopathy. Recently, dominant SLC2A1 mutations were found in rare autosomal dominant families with various forms of epilepsy including early onset absence epilepsy (EOAE), myoclonic astatic epilepsy (MAE), and genetic generalized epilepsy (GGE). Our study aimed to investigate the possible role of SLC2A1 in various forms of epilepsy including MAE and absence epilepsy with early onset. We also aimed to estimate the frequency of GLUT1 deficiency syndrome in the Danish population. One hundred twenty patients with MAE, 50 patients with absence epilepsy, and 37 patients with unselected epilepsies, intellectual disability (ID), and/or various movement disorders were screened for mutations in SLC2A1. Mutations in SLC2A1 were detected in 5 (10%) of 50 patients with absence epilepsy, and in one (2.7%) of 37 patient with unselected epilepsies, ID, and/or various movement disorders. None of the 120 MAE patients harbored SLC2A1 mutations. We estimated the frequency of SLC2A1 mutations in the Danish population to be approximately 1:83,000. Our study confirmed the role of SLC2A1 mutations in absence epilepsy with early onset. However, our study failed to support the notion that SLC2A1 aberrations are a cause of MAE without associated features such as movement disorders.
SUMMARYPurpose: Neurexins are neuronal adhesion molecules located in the presynaptic terminal, where they interact with postsynaptic neuroligins to form a transsynaptic complex required for efficient neurotransmission in the brain. Recently, deletions and point mutations of the neurexin 1 (NRXN1) gene have been associated with a broad spectrum of neuropsychiatric disorders. This study aimed to investigate if NRXN1 deletions also increase the risk of idiopathic generalized epilepsies (IGEs). Methods: We screened for deletions involving the NRXN1 gene in 1,569 patients with IGE and 6,201 controls using high-density oligonucleotide microarrays.Key Findings: We identified exon-disrupting deletions of NRXN1 in 5 of 1,569 patients with IGE and 2 of 6,201 control individuals (p = 0.0049; odds ratio (OR) 9.91, 95% confidence interval (CI) 1.92-51.12). A complex familial segregation pattern in the IGE families was observed, suggesting that heterozygous NRXN1 deletions are susceptibility variants. Intriguingly, we identified a second large copy number variant in three of five index patients, supporting an involvement of heterogeneous susceptibility alleles in the etiology of IGE. Significance: We conclude that exon-disrupting deletions of NRXN1 represent a genetic risk factor in the genetically complex predisposition of common IGE syndromes.
We performed a clinical and molecular genetic analysis in members of five families with dopa-responsive dystonia. Four mutations were detected in the gene GCH1 that codes for GTP cyclohydrolase I. Two of these mutations, a delG309 in exon 1 and a C544T transition in exon 5, have not been described before. They result in inactivation of the enzyme by truncation. The remaining two mutations, both A to G transitions, a(-2)g in intron 1 and a(-2)g in intron 2, cause truncation by abnormal splicing. The genotype of family members was correlated to their clinical phenotype (obtained before molecular analysis). Clinical symptoms observed in the families included generalized and focal dystonia, abnormal gait, and subtle signs such as an abnormal writing test. High penetrance (0.8-1.0) was observed in four of five families if minor symptoms and signs were considered. A given mutation was more likely to cause symptoms in females than in males, thus confirming the well-established higher incidence of dopa-responsive dystonia in females than in males.
Summary: Purpose: Valproic acid (VPA) is an antiepileptic drug (AED) commonly used for generalized and focal epilepsies. We provide an update on hepatotoxic side effects in Germany between 1994 and 2003. Methods: We mailed a questionnaire to all members of the German Section of the International League Against Epilepsy, asking for VPA‐induced side effects, especially severe side effects such as hepatopathy. Results: As a result of our questionnaire, we found 31 cases of reversible hepatotoxicity and nine cases of lethal hepatopathies in Germany from 1994 to 2003. Conclusions: The outcome of patients with severe hepatotoxicity is better than that in the past. The risk of a VPA‐induced hepatopathy is not limited to patients younger than 2 years, receiving polytherapy, or patients with congenital or acquired metabolic diseases.
We describe two previously unrecognized splice site mutations of GCH1 in Dopa responsive dystonia (DRD). Both mutations affect consensus splice acceptor (AG) sites. The first mutation is an A-->G transition at position -2 of intron 1 of GCH1. This mutation results in skipping of exon 2. Fusion of exons 1 and 3 causes a frame shift that generates a premature stop codon. The second mutation is an A-->G transition at position -2 of intron 2. The mutation generates a new splice acceptor site AG one base pair upstream of the wild-type splice site. This, together with a pyrimidine stretch upstream of the new splice site, renders this site functional and generates a transcript with the insertion of one base, i.e. the G of the wild-type splice site. This in turn causes a frame shift including the introduction of a premature stop codon. The two different mutations generate truncated GTP cyclohydrolase polypeptides.
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