C9orf72 and amyotrophic lateral sclerosis: Up to 15% of ALS patients also develop signs of frontotemporal dementia (FTD) (3) and several genes, including C9ORF72, TDP-43, VCP, SQSTM1, OPTN, UBQLN2 and TBK1, contribute to the etiology of both ALS and FTD (4–6).