that African Americans displayed a lower degree of methylation between cases and controls (Nielsen et al., 2010). Taken together, at this time, the results of association studies do not support the Asn40Asp SNP as a risk factor for alcoholism and other substance use disorders. Nevertheless, it remains puzzling that some studies found support for an association while others did not. Further elucidation of additional moderating variables, such as sex, environmental differences, ethnicity, and epistatic effects, may allow us to reconcile these disparate findings.
