C9orf72 and amyotrophic lateral sclerosis: The most commonly studied genes with causal links to ALS include: Superoxide dismutase 1 (SOD1; ~20% of fALS and 1–4% sALS), Fused in sarcoma (FUS; ~1–5% of fALS and ~1% sALS cases),TAR DNA binding protein 43 (TARDBP; ~4–5% of fALS and 2% sALS cases) and chromosome 9 open reading frame 72 (C9orf72; 1 in 10 of ALS cases among European-ancestry populations) [14,15].