The amyloid precursor protein (APP) gene codes for the precursor to the beta-protein found in the amyloid deposits of Alzheimer disease (AD). Recently Goate et al. identified in codon 717 of this gene a missense mutation which segregates with AD in a familial AD (FAD) kindred. The same mutation was also found in affected subjects from a second FAD family but not in other FAD families or in normal controls. The following work was undertaken to determine the frequency of the codon 717 mutation in FAD and nonfamilial AD cases and in normal controls. We tested 76 FAD families, 127 "sporadic" AD subjects, 16 Down syndrome cases, and 256 normal controls for this mutation, and none were positive. We also tested for the APP codon 693 mutation associated with hereditary cerebral hemorrhage with amyloidosis-Dutch type, for PRIP gene missense mutations at codons 102, 117, and 200, and for the PRIP insertion mutations which are associated with Creutzfeld-Jakob disease and Gerstmann-Straussler Scheinker syndrome. No examples of these mutations were found in our population. Thus these APP and PRIP mutations are rare in both FAD and nonfamilial AD.