While mutations of the PS-1, PS-2,11 and APP genes (resulting in increased production and elevated plasma levels of Aβ protein) on chromosomes 1, 14, and 21, respectively, have been associated with the rare form of familial AD, the only consistent marker for the late-onset non-familial form of AD is the apo-E allele on chromosome 19. This evidence concerns the gene APP and Alzheimer disease.