5–10% of ALS cases are familial (fALS), of which most are associated with repeat expansions of the C9ORF72 gene or mutations in genes encoding copper–zinc superoxide dismutase (SOD1), TAR DNA binding protein 43 (TDP-43) or fused in sarcoma (FUS; Al-Chalabi et al., 2012). Here, FUS is linked to amyotrophic lateral sclerosis.