C9orf72 and frontotemporal dementia: The mean age was 49.2 ± 11.7 years for the control group, 56.1 ± 11.1 years for the FTD‐C9orf72 group, 61.4 ± 10.7 years for the FTD‐GRN group, and 54.5 ± 7.8 years for the FTD‐MAPT group.