Genotype–environment correlations: implications for determining the relationship between environmental exposures and psychiatric illness

Psychosocial risk factors for psychiatric illness are moderately heritable. This has two implications: first, that individuals actively shape their environments through heritable behaviour; second, that the relationship between environmental exposure and psychopathology may be confounded by genotype. We define three types of genotype–environment correlation (passive, evocative, and active), describe the evidence from quantitative and molecular genetic studies for their existence, and discuss the implications of genotype–environment correlations for the prevention and treatment of psychiatric disorder. Research designs are needed that can test which exposures have truly causal effects on mental illness and which are confounded by genotype, so that clinicians can make informed decisions about when modifying exposures will be likely to result in reductions in mental illness. By considering bi-directional and reciprocal relations between risk exposures and patients’ behaviour, clinicians may develop a fuller picture of the causes of disorder and develop more effective treatment methods.