ABSTRACT
A chromosomal translocation t(18;21)(q23;q22) is reported in a patient with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). We exclude the physical involvement and silencing of the ALS-linked gene for copper/zinc superoxide dismutase (SOD1) on chromosome 21q22.1. The breakpoints are assigned to sequences flanked by the markers ATA1H06, D18S462, D21S1915, and D21S1898. These critical regions may contain susceptibility loci for FTD associated with ALS.
Subject(s)
Amyotrophic Lateral Sclerosis/genetics , Brain/pathology , Dementia/genetics , Translocation, Genetic , Amyotrophic Lateral Sclerosis/complications , Amyotrophic Lateral Sclerosis/physiopathology , Blotting, Southern , Chromosomes, Human, Pair 18 , Chromosomes, Human, Pair 21 , Dementia/complications , Dementia/physiopathology , Humans , In Situ Hybridization, Fluorescence , Karyotyping , Magnetic Resonance Imaging , Reverse Transcriptase Polymerase Chain Reaction , Superoxide Dismutase/genetics , Superoxide Dismutase-1 , Tomography, Emission-ComputedABSTRACT
Idiopathic generalized epilepsy (IGE) is an inherited neurological disorder affecting about 0.4% of the world's population. Mutations in ten genes causing distinct forms of idiopathic epilepsy have been identified so far, but the genetic basis of many IGE subtypes is still unknown. Here we report a gene associated with the four most common IGE subtypes: childhood and juvenile absence epilepsy (CAE and JAE), juvenile myoclonic epilepsy (JME), and epilepsy with grand mal seizures on awakening (EGMA; ref. 8). We identified three different heterozygous mutations in the chloride-channel gene CLCN2 in three unrelated families with IGE. These mutations result in (i) a premature stop codon (M200fsX231), (ii) an atypical splicing (del74-117) and (iii) a single amino-acid substitution (G715E). All mutations produce functional alterations that provide distinct explanations for their pathogenic phenotypes. M200fsX231 and del74-117 cause a loss of function of ClC-2 channels and are expected to lower the transmembrane chloride gradient essential for GABAergic inhibition. G715E alters voltage-dependent gating, which may cause membrane depolarization and hyperexcitability.
