To do this, we used positron emission tomography (PET) with the radioligand [11C]UCB‐J, which binds to synaptic vesicle protein 2A, in three asymptomatic carriers of C9orf72 mutations, a patient with symptomatic frontotemporal dementia, and 19 healthy controls. Here, C9orf72 is linked to frontotemporal dementia.