Research designs for the study of gene-environment interactions in psychiatric disorders. Report of a Foundations Fund for Research in Psychiatry Panel.

Understanding the genetic and environmental contributions (and their interactions, which are likely to be complex) to the etiology of psychiatric disorders requires research designs incorporating many basic principles of genetics. Genetic variation is likely to contribute to psychiatric disorders and genetic heterogeneity is likely to exist for any single disorder, ie, completely different genetic variants may each be capable of increasing an individual's susceptibility to the disorder. Thus, it is important to define phenotypes that may more closely reflect each individual genetic variant rather than to rely solely on the psychiatric diagnosis. Research should be undertaken with the goal of testing specific hypotheses that can be excluded. Research designs can include studies of unrelated individuals, twins, separated relatives, nuclear families, or extended pedigrees. Not all hypotheses can be tested on one type of data, and appropriate analytic methods vary. Because genetic hypotheses cannot be tested on studies of unrelated individuals, it is important that data be collected on families instead of unrelated individual patients and/or controls. Studies should include traits that bridge the gap between the genotype and the diagnostic phenotype. Such studies should be multidisciplinary, and the best statistical-genetics methodology should be used for data analysis.