In the underlying white matter, increasedfibrinogen correlated with reduced oxygenation, but PDGFRB level was unchanged.The level of platelet-derived growth factor-ββ (PDGF-BB), important for pericytemaintenance, was increased in AD but mainly in the insoluble tissue fraction,correlating with insoluble Aβ level. The gene discussed is PDGFRB; the disease is Alzheimer disease.