The majority of ALS/FTD cases are sporadic, with only 5–10%of all cases running in families. FamilialALS/FTD is linked to mutations in many genes including fusedin sarcoma (FUS), TAR DNA-binding protein 43 (TDP-43), and chromosome 9 open reading frame 72 (c9orf72). The gene discussed is C9orf72; the disease is frontotemporal dementia.