An atypical posterior variant of Alzheimer’s disease was defined in the 2014 diagnostic criteria,10 but it is only with the emergence of amyloid and tau PET tracers, alongside CSF and now plasma biomarkers for Alzheimer’s disease,11,12 that CBS associated with versus without Alzheimer’s disease pathology13 can be identified. The gene discussed is MAPT; the disease is early-onset autosomal dominant Alzheimer disease.