Mutations in senataxin responsible for Quebec cluster of ataxia with neuropathy

Senataxin recently was identified as the mutated gene in ataxia‐oculomotor apraxia 2, which is characterized by ataxia, oculomotor apraxia, and increased α‐fetoprotein levels. In this study, we evaluated 24 ataxic patients from 10 French‐Canadian families. All cases have a homogeneous phenotype consisting of a progressive ataxia appearing between 2 and 20 (mean age, 14.8) years of age with associated dysarthria, saccadic ocular pursuit, distal amyotrophy, sensory and motor neuropathy, and increased α‐fetoprotein levels but absence of oculomotor apraxia. Linkage disequilibrium was observed with markers in the ataxia‐oculomotor apraxia 2 locus on chromosome 9q34. We have identified four mutations in senataxin in the French‐Canadian population including two novel missense mutations: the 5927T→G mutation changes the leucine encoded by codon 1976 to an arginine in the helicase domain (L1976R), and the 193G→A mutation changes a glutamic acid encoded by codon 65 into a lysine in the N‐terminal domain of the protein (E65K). The common L1976R mutation is shared by 17 of 20 (85%) carrier chromosomes. The study of this large French‐Canadian cohort better defines the phenotype of this ataxia and presents two novel mutations in senataxin including the more common founder mutation in the French‐Canadian population. Ann Neurol 2005;57:408–414