In this study, all of our cases were symptomatic (CDR ≥ 1), although we note that behavioral and cognitive changes can emerge in the presymptomatic and prodromal stages of bvFTD, many years before dementia and diagnosis29, 30; and synaptic loss has been identified in the presymptomatic stage of those with highly penetrant mutations such as C9orf72 expansions.16 Here, C9orf72 is linked to dementia.