Models for the joint effect of genotype and environment on liability to psychiatric illness.

The authors present three major models for the joint effect of genes and environment on liability to psychiatric illness: additive effects of genotype and environment, genetic control of sensitivity to the environment, and genetic control of exposure to the environment. Each model is illustrated by several examples, including a quantitative one. The authors attempt to demonstrate that genes and the environment can interact in several interesting and potentially subtle ways, that these interactions can be expressed in simple models from which clear empirical predictions can be generated, and that elucidation of the etiology of psychiatric disorders will require the consideration of both genetic and environmental risk factors.