In carriers of the C9orf72 HRE, the CC genotype at rs12608932 (n = 81/690) was associated with significantly higher risk of all four outcomes: ALS [Plog-rank = 0.038, HR = 2.00 (1.09–3.66)], FTD [Plog-rank = 0.063, HR = 2.03 (1.10–3.73)], dementia [Plog-rank = 0.011, HR = 2.11 (1.24–3.58)] and ALS or dementia [Plog-rank = 0.008, HR =1.85 (1.20–2.85)], although for FTD only Cox analyses reached statistical significance, likely due to lower power. This evidence concerns the gene C9orf72 and frontotemporal dementia.