Individual C9orf72 mutation carriers are grouped by their clinical diagnosis at enrollment with values at baseline and 6-, 12-, and 18-month follow-up. Black circles represent asymptomatic carriers; red squares, ALS; green diamonds, ALS-FTD; and blue triangles, bvFTD. (A) ALS functional rating scale. (B) Letter fluency. (C) FBI, expressed as percent of possible total score because items affected by motor function in each patient were excluded. ALS = amyotrophic lateral sclerosis; ALSFRS-R = Revised ALS Functional Rating Scale; bvFTD = behavior-variant frontotemporal dementia; FBI = Frontal Behavioral Inventory; FTD = frontotemporal dementia.