We hypothesized that pain and temperature symptoms would be over-represented in behavioural variant FTD and semantic dementia versus progressive non-fluent aphasia (PNFA) and Alzheimer’s disease, and more specifically, in patients with C9orf72 mutations versus other disease groups; and that behavioural variant FTD and semantic dementia have overlapping but differentiable symptom profiles characterized by blunted versus heightened pain and temperature responsiveness, respectively. Here, C9orf72 is linked to early-onset autosomal dominant Alzheimer disease.