with only a genetic predisposition (Cadoret et al. 1990). In an adoption study of Swedish men, mild and severe alcohol abuse were more prevalent only among men who had both a genetic predisposition and more disadvantaged adoptive environments (Cloninger et al. 1981). The Finnish Adoptive Family Study of Schizophrenia found that high genetic risk was associated with increased risk of schizophrenic thought disorder only when combined with communication deviance in the adoptive family (Wahlberg et al. 1997). Additionally, the adoptees had a greater risk of psychological disturbance, defined as neuroticism, personality disorders, and psychoticism, when the adoptive family environment was disturbed (Tienari et al. 1990). These studies have demonstrated that genetic predispositions for a number of psychiatric disorders interact with environmental influences to manifest disorder.
