necessary to conduct a GWAS study with sufficient statistical power. In GWAS studies of psychopathology phenotypes conducted to date, this problem is further exacerbated by small effect sizes necessitating further increase in sample size in order to detect a significant effect. Although there is some hope that effect sizes for “brain-based” phenotypes may be larger, for the study of psychophysiology phenotypes the GWAS approach remains cost-prohibitive, though not impossible, especially if multi-center collaboration using a standardized set of measures is established. A compromise approach would be an extended version of the candidate gene design, with multiple genes selected based on bioinformatics evidence for their involvement in the biological pathway relevant to the studied phenotype. A sufficiently dense coverage of these genes may reduce the number of markers to thousands or perhaps even hundreds, which may be a realistic number for a study involving hundreds, rather than thousands, of subjects. For a more detailed description of genetic concepts and methods, as well a thorough discussion of the strengths and weaknesses of different approaches to the study of genetic association, the reader is referred to appropriate review articles (Attia et al., 2009a, b, c; Hardy and Singleton, 2009; Hirschhorn and Daly, 2005;
