Cerebrospinal fluid, plasma, and blood biomarkers used in AD diagnosis include Aβ42 concentration, Aβ42/Aβ40 ratio, phosphorylated Tau, or phospho-Tau (P-Tau), total Tau (t-Tau), P-Tau ratio, neurofilaments, synaptic proteins, presence of inflammatory markers, and activated astrocytes. The gene discussed is MAPT; the disease is Alzheimer disease.