For instance, a lower amyloid-β 42/amyloid-β 40 ratio (Aβ42/Aβ40 ratio) indicates a greater amyloid burden in the brain, a higher phosphorylated tau (p-tau) level indicates a greater tangle pathology in the brain, and a higher phosphorylated tau/amyloid-β 42 ratio (p-tau/Aβ42 ratio) indicates a greater Alzheimer’s disease pathology. The gene discussed is MAPT; the disease is early-onset autosomal dominant Alzheimer disease.