C9orf72 and Brain atrophy: Symptom onset can range from 20 to 90 years of age and the mean age of onset of FTD-C9orf72 is 58.2 ± 9.8 years, with a mean disease duration of 6.4 years (n = 618).49 The pathogenic expansion is almost fully penetrant by 80 years of age.59 Brain atrophy in FTD-C9orf72 carriers occurs earlier than in other mutation groups, appearing before age 40 and potentially 25 years before clinical symptoms.60