ABCA2 and Alzheimer disease: The cause for most AD cases is still largely unknown, although attempts have been made to explain AD by using the hypotheses based on acetylcholine [5], amyloid [6], [7], tau [7] and etc. In the present study, we performed meta-analyses for the variants on 6 protein encoding genes, including choline O-acetyltransferase (CHAT), catechol-O-methyltransferase (COMT), alpha-2-macroglobulin (A2M), 5-hydroxytryptamine receptor 6 (HTR6), ATP-binding cassette, sub-family A, member 2 (ABCA2), lipoprotein lipase (LPL).