MAPT and early-onset autosomal dominant Alzheimer disease: Tau, the principle microtubule-associated protein in neurons, is regulated by phosphorylation in its physiologically normal binding to microtubules (2, 3) and driven by hyperphosphorylation to form cytotoxic amyloid filaments and tangles associated with Alzheimer’s disease and other tauopathies (2, 4, 5, 6).