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Objective: To perform an extensive screening for mutations of amyotrophic lateral sclerosis (ALS)-related genes in a consecutive cohort of Sardinian patients, a genetic isolate phylogenically distinct from other European populations. Design: Population-based, prospective cohort study. Patients: A total of 135 Sardinian patients with ALS and 156 healthy control subjects of Sardinian origin who were age- and sex-matched to patients. Intervention: Patients underwent mutational analysis for SOD1, FUS, and TARDBP. Results: Mutational screening of the entire cohort found that 39 patients (28.7%) carried the c.1144G>A (p.A382T) missense mutation of the TARDBP gene. Of these, 15 had familial ALS (belonging to 10 distinct pedigrees) and 24 had apparently sporadic ALS. None of the 156 age-, sex-, and ethnicity-matched controls carried the pathogenic variant. Genotype data obtained for 5 ALS cases carrying the p.A382T mutation found that they shared a 94-single-nucleotide polymorphism risk haplotype that spanned 663 Kb across the TARDBP locus on chromosome 1p36.22. Three patients with ALS who carry the p.A382T mutation developed extrapyramidal symptoms several years after their initial presentation with motor weakness. Conclusions: The TARDBP p.A382T missense mutation accounts for approximately one-third of all ALS cases in this island population. These patients share a large risk haplotype across the TARDBP locus, indicating that they have a common ancestor. [ABSTRACT FROM AUTHOR]