The majority of ALS cases are sporadic, while 10% are of the familial form; these familial cases are linked to a variety of genes such as Cu/Zn superoxide dismutase 1 (SOD1; Rosen, 1993), TAR DNA-binding protein 43 (TDP-43) (Mackenzie et al., 2007), C9orf72 hexanucleotide repeat expansion (DeJesus-Hernandez et al., 2011; Renton et al., 2011) and others. The gene discussed is C9orf72; the disease is amyotrophic lateral sclerosis.