One possibility that has not been extensively researched is that people with a genetic predisposition to internalizing psychopathology (i.e., a higher loading on the spectrum) will express that pathology in the face of difficult or troubling circumstances in their lives. This is a question of gene × environment interaction (G×E), also known as biometrical moderation, or genetic susceptibility to environmental stressors. In one example of this type of model, Heath, Eaves, and Martin (1998) found smaller effects of genetic influence on depression in married vs. unmarried women. Using a sample of female Australian twin pairs, they divided the sample into pairs concordant for a marriage-like partnership, concordant for no relationship, and discordant. The proportion of total variance in depression due to genetic influences increased from 29% in married twins to 51% in unmarried twins over 31 years of age. Marriage, therefore, acted as a protective factor by reducing the genetic liability to depressive symptoms. Surprisingly, there have been no studies since Heath et al. (1998) to expand on this interesting notion of the marital relationship as a protective factor in diminishing genetic influences.
