SOD1 and amyotrophic lateral sclerosis: Three ALS causative genes linked to over 50% of the F-ALS patients [24] were included in the validation cohort, namely 13% with the most common gene variant chromosome 9 open reading frame 72 (C9orf72), 9% superoxide dismutase 1 (SOD1) and 4% TAR DNA binding protein (TARDBP), while the remaining 35 patients were classified as S-ALS.