The association between age of onset and rs9357140 was evident in unrelated C9orf72 patients with either pure ALS (n = 59; adjusted P = 0.002, B = 4.97, SE: 1.53) or pure FTD (n = 174; adjusted P = 0.0008, B = 2.82, SE: 0.83), but not in patients with FTD-ALS (n = 71; adjusted P = 0.125, B = 2.63, SE: 1.69) (Supplementary Table 1 and Supplementary Fig. 4A–C). Here, C9orf72 is linked to frontotemporal dementia.