Using Alzgene-like approaches to investigate susceptibility genes for vascular cognitive impairment.

Vascular cognitive impairment (VCI), including vascular dementia, is the second most common dementia after Alzheimer's disease. Despite its prevalence, the genetic etiology of sporadic VCI is largely unknown. We conducted a systematic review of all published genetic association studies of forms of sporadic VCI prior to 6 July 2012. An initial pool of 229 gene association studies yielded 104 papers (72 polymorphisms from 47 genes) that met inclusion criteria for analysis. Systematic meta-analysis was conducted on 6 polymorphisms (which had 3 or more published case-control cohorts from 69 papers) in the APOE, ACT, ACE, MTHFR, PON1, and PSEN-1 genes. Associations of increased risk for VCI were found for APOE ε4 (1.818 (95% CI = 1.611-2.053), p < 0.001; n = 3,554 cases, n = 12,277 controls) and MTHFR rs1801133 (1.323 (95% CI = 1.061-1.650) p = 0.013); n = 659 cases, n = 981 controls). There was marginal evidence of a protective effect for APOE ε2 (0.885 (95% CI = 0.783-0.999), p = 0.048; n = 3,320 cases, n = 10,786 controls). This systematic study of all published genetic association studies of sporadic VCI supports MTHFR and APOE as susceptibility genes for VCI. It also shows the utility of meta-analysis as a tool to identify potential candidate genes from numerous individual small-scale studies of diseases where sample recruitment may be limited for a variety of practical reasons.