For example, more than 40% of Sardinian patients with ALS have a mutation in a known ALS gene (TDP43 or C9orf72).21 Similarly, Northern Finland exhibits high rates of C9orf72 repeat expansions and Northern Sweden has high rates of SOD1 mutations.22 Recognition of the presence of a likely founder within a region could inform both genetic counseling and testing. This evidence concerns the gene TARDBP and amyotrophic lateral sclerosis.