Although molecular basis of AD remains largely unclear, there is considerable evidence which supports the so-called “amyloid cascade hypothesis”: AD may be viewed as a metabolic vicious cycle in which β-amyloid (Aβ) deposition into senile plaques drives neurodegeneration by triggering abnormal microglia activation, tau protein hyperphosphorylation and the consequent death of astrocytes and neurons. The gene discussed is MAPT; the disease is Alzheimer disease.