Familial ALS (fALS), caused by genetic mutations in genes such as Cu2+/Zn2+ SOD-1, TAR DNA binding protein-43 (TDP-43), and GGGGCC repeat expansions in the C9orf72 locus, represents 5%–10% of total ALS cases, whereas sporadic ALS (sALS), which is unassociated with any known genetic mutations, represents approximately 90% of ALS cases. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.