ABCA1 and Alzheimer disease: We suggest three possible reasons for the differing results: 1) the ABCA1 rs2230806 SNP does affect risk for AD, but the effect is small so that the association cannot be reproduced regularly in samples of ~2500 subjects; or 2) the population we examined was genetically different from the populations in the other studies assessed; or 3) the ABCA1 rs2230806 SNP does not affect risk for AD.