It seems that, in addition to the age-related decrease of P-gp expression, Aβ1–42 itself downregulates the expression of P-gp and other Aβ transporters, which could exacerbate the intracerebral accumulation of Aβ and thereby accelerate neurodegeneration in AD and cerebral Aβ angiopathy. The gene discussed is PGP; the disease is Alzheimer disease.