MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer disease (AD)2 is a debilitating, neurodegenerative disorder that is characterized by two prominent forms of fibrillar brain lesions: amyloid plaques composed of the peptide amyloid β (Aβ) and neurofibrillary tangles that contain hyperphosphorylated forms of the microtubule-associated protein tau (1).