It is now clear that genomewide association studies (GWAS) can be a successful tool in the genetic dissection of complex biomedical disorders (17, 18). The goal of this report is to describe a GWAS for MDD that was systematically designed to remediate a set of methodological issues common to genetic studies of MDD. Examples of these issues include small sample sizes, inhomogeneous samples in terms of ancestry and phenotyping, convenience sampling, and controls that are unaffected but not at low liability for MDD. Moreover, large-scale replication was integral to our design.
