Studies of G × E in humans are not confined to the study of multifactorial liability and the structural modeling of the patterns of covariance between relatives but extend to the detection and analysis of interaction between candidate genes and environmental covariates. Such studies enjoy a high profile and the generated enthusiasm influences the direction and funding of subsequent research in psychiatric and behavioral genetics. With this in mind, and knowing the inherent problems of interpreting interactions in twin and family studies, this paper explores the extent to which the same uncertainties attend apparent demonstrations of interaction between candidate genes and covariates in psychiatric genetics.
