MAPT and behavioral variant of frontotemporal dementia: Larger studies in C9orf72 FTD might expand upon these results, as C9orf72 frontotemporal dementia is clinically and neuroanatomically heterogeneous.20 While our C9orf72 case is young, mutation positive, and meets diagnostic criteria for definite behavioral variant frontotemporal dementia, we lack biomarker or pathology proof of the absence of coincidental Alzheimer tau pathology that may occur in a small percentage of adults in their fifties.