APP and Alzheimer disease: Concerning the two other human proteins that have a high degree of homology to APP but do not contain the Aβ sequence: APLP1 and APLP2, and in regard to the pathology of AD, although APLP1 and APLP2 do not produce the toxic Aβ peptide, their roles in functioning separately from, but in support of, APP suggest that they may play a role in the development of the disease.