C9orf72 and Atrophy: The current presymptomatic cohort represents a heterogeneous sample with 39 (9 C9orf72, 22 GRN, 8 MAPT) of 130 participants within 5 years of their expected age at onset, when atrophy is more likely to be present, while 33 participants (12 C9orf72, 15 GRN, and 6 MAPT) are more than 20 years away from expected onset, where atrophy should be minimal.