C9orf72 and amyotrophic lateral sclerosis: The cause of ALS is largely unknown, although defective genes have been identified in a small percentage of familial ALS cases, including those encoding superoxide dismutase 1 (SOD1), TAR DNA-Binding Protein (TARDBP), fused in sarcoma (FUS), Ubiquilin2 (UBQLN2) and C9ORF72 (Chen et al., 2013).