Because 18F-AV-1451 binds to hyperphosphorylated paired helical filament tau and neurofibrillary tangles (73), and tau pathology—but not amyloid—is at disproportionate higher concentration in posterior brain regions in PCA (5, 7), the tau-PET has the additional potential to distinguish PCA from other AD variants. The gene discussed is MAPT; the disease is Alzheimer disease.