Recent in vivo PET imaging in Alzheimer’s disease using 11C-UCB-J as a marker of synaptic density and 18F-AV-1451 or 18F-MK-6240 PET as markers of tau pathology have shown decreased temporal lobe synaptic density with increasing pathological burden,21 but with individual variability depending on the severity of cortical pathology.22 Here, MAPT is linked to early-onset autosomal dominant Alzheimer disease.