After the discovery of the key roles of alpha-synuclein in Lewy body pathology in PD and related disorders (MSA, PSP) and tau, phosphorylated-tau and amyloid-beta (1-42) in neurofibrillary tangles and plaques in Alzheimer’s disease (AD), major research efforts have been directed to the measurements of these proteins in body fluids, particularly in CSF. The gene discussed is MAPT; the disease is Alzheimer disease.