C9orf72 and amyotrophic lateral sclerosis: Some have been linked to gene mutations which account for a share of both familial (23% by C9orf72 mutations, 4% by FUS/TLS, 20% by SOD1 and 5% by TDP-43) and sporadic (5–7% by C9orf72, 1% by SOD1 and 2% by TDP-43) variants of ALS (Turner et al., 2013).