C9orf72 and amyotrophic lateral sclerosis: Moreover, various missense mutations have been identified in SOD1, TDP-43, and FUS, as well as a hexanucleotide repeat expansion in C9orf72, which increase the aggregation propensity of these proteins and are associated with familial ALS (fALS) accounting for 10% of all ALS cases (Sibilla and Bertolotti, 2017).