While C9orf72 ALS cases had shorter disease duration compared with SOD1 and TDP-43-related ALS cases, and an older age of onset compared with SOD1 and FUS-related ALS, the consistent finding in this analysis was the increased incidence of FTD or a family history of dementia identified in the patients with C9orf72 ALS. Here, C9orf72 is linked to frontotemporal dementia.