The identification of the familial genes has helped to formulate, and then strengthen, the amyloid cascade hypothesis of AD aetiopathology, which holds that it is an increase in the generation (or a reduction in the clearance) of β-amyloid, or a relative increase in the more amyloidogenic forms of β-amyloid in brain, that initiates the disease process, resulting in the aberrant phosphorylation of tau and its intracellular aggregation in the form of neurofibrillary tangles (NFTs) [13]. The gene discussed is MAPT; the disease is Alzheimer disease.