C9orf72 and amyotrophic lateral sclerosis: Although most of ALS patients are sporadic (sALS) of unknown onset, ∼10% of ALS cases are familial (fALS), and over 30 potential ALS genes, such as TARDBP (which encodes TDP-43), SOD1, C9ORF72, OPTN, UBQLN2, and so on, have been identified (Cirulli et al., 2015).