SOD1 and amyotrophic lateral sclerosis: The most frequent mutation is a toxic hexanucleotide repeat expansion in the C9ORF72 gene, accounted by up to 35% of familial cases, followed by mutations in the Cu/Zn-superoxide dismutase 1 (SOD1) gene (15–30% of fALS and up to 2% of the total of ALS cases) [2,3], although these numbers might be underestimated due to the current limitations of genetic testing in sporadic cases.