A variety of study designs have been employed to identify genes influencing the vulnerability to AD. Genome-wide association studies (GWAS) are a potentially more comprehensive way to study a complex, common disease like AD where we have little knowledge of disease pathophysiology. Several GWAS have sought to identify variants associated with the risk for AD using case-control designs, including treatment seeking subjects with AD9, individuals selected from densely affected families with AD10, a case-control series drawn from treatment and community-based samples from several diseases11, subjects ascertained from large unselected sibships as well as individuals selected for heavier alcohol use12. GWAS using quantitative traits derived from alcohol consumption and AD symptomatology have also been examined in a population-based sample13 and an Australian sample of related individuals12. Results thus far have identified interesting candidate genes for AD, although the overlap of the top genetic signals across studies has been limited.
