Frequency of C9orf72 hexanucleotide repeat expansion and SOD1 mutations in Portuguese patients with amyotrophic lateral sclerosis

Abstract

Mutation frequency of the 2 main amyotrophic lateral sclerosis (ALS)-related genes, C9orf72 and SOD1, varies considerably across the world. We analyzed those genes in a large population of Portuguese ALS patients (n = 371) and recorded demographic and clinical features. Familial ALS (FALS) was disclosed in 11.6% of patients. Mutations in either SOD1 or C9orf72 were found in 9.2% of patients and accounted for 40% of FALS and 5.2% of sporadic ALS. SOD1 mutations were rare (0.83%), but a novel and probably disease-causing mutation was identified: p.Ala152Pro (c.457G>C). The C9orf72 hexanucleotide repeat expansion was the commonest abnormality, accounting for 4.6% of sporadic ALS and 37.5% of FALS; in these patients, Frontotemporal Dementia was prevalent. This first report on the frequency of C9orf72 hexanucleotide repeat expansion and SOD1 mutations in Portuguese ALS patients reiterate that the genetic architecture of ALS varies among different geographic regions. The mutations incidence in ALS patients (∼10%) and associated phenotypes suggest that genetic tests should be offered to more patients, and other genes should be investigated in our population.

Keywords: Amyotrophic lateral sclerosis; C9orf72 hexanucleotide repeat expansion; Frontotemporal dementia; Mutation; Phenotype; SOD1.