Since 1984, a diagnosis of probable Alzheimer disease has been based on clinical findings of a progressive amnestic multidomain cognitive impairment culminating in dementia after other potential causes were excluded.1,2,3 Neuropathologic identification of β-amyloid plaques and tau tangles has always been required for a definite diagnosis of Alzheimer disease. The gene discussed is MAPT; the disease is early-onset autosomal dominant Alzheimer disease.