Research advances in the biology of Alzheimer's disease.

Research on AD has shed light on the biochemical composition and mechanisms of the formation of amyloid deposits and PHFs, the structural hallmarks of the disease. Amyloid is composed of a 4-kd peptide, beta P, that originates in the metabolism of a 130-kd transmembrane precursor protein. Soluble beta P accumulates in the AD brain until it polymerizes in amyloid fibers. Paired helical filaments are composed of hyperphosphorylated tau, a microtubule-associated protein that normally acts as a tubulin assembly factor. Future research must clarify why beta P accumulates in extracellular spaces of AD tissue and focus on the relation between amyloid deposition and neuronal degeneration.