Genetic Factors

Genetic Factors

The familial nature of mood disorders has long been observed. It has been established that bipolar I disorder is more heritable than the other mood disorders, that an early age of onset is associated with greater heritability, and that heritable risk decreases in proportion to the amount of genetic material shared by members of a pedigree (Kelsoe, 2000). Genetic factors can interact with environmental factors to influence the vulnerability to mood disorders in different ways. For example, Kendler (1998) explored two such mechanisms: “genetic control of sensitivity to environment”, and “genetic control of exposure to the environment”. “Genetic control of sensitivity to the environment” suggests that genes, in part, render individuals relatively vulnerable or relatively invulnerable to the pathogenic ef-fects of environmental stress. The depressogenic effect of stressful life events is substantially greater in those at high versus low genetic risk to the mood disorders. “Genetic control of exposure to the envi-ronment” suggests that genetic factors influence the probability that individuals will select themselves into high versus low risk environ-ments. The genetic risk factors for major depression in part express themselves by influencing the probability that individuals will expe-rience stressful life events, particularly of an interpersonal nature.