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Question: What is the role of genetics in mood disorders?

Keh-Ming Lin, M.D., M.P.H.: A person’s psychological and behavioral characteristics are significantly influenced by genetic factors, similar to many physical traits, such as height, weight, and hair and eye color. These influences, however, are strongly affected by environmental forces – even identical twins will show significant differences in their temperaments, behaviors and risks for psychiatric problems such as mood disorders. Genetic factors generally account for approximately half of these differences, according to family and twin studies.

With the completion of the Human Genome Project (the mapping of human DNA), science is rapidly moving toward identifying specific variations in the genes that help to make each one of us different and unique. Some of these variations occur in genes that affect the function of the brain (and the production of chemicals related to mood such as serotonin and norepinephrine), and are likely to be associated with risks for mood disorders.

It’s important to keep in mind that there are no specific “disease genes” for mood disorders. Rather, all genes contain variations, and only some of them might prove to be relevant. Each variation increases a person’s disease risk only a small amount. Typically, the combined effects of a person’s multiple genes and his or her interaction with the environment determine the risk for a mood disorder. This is also the case with illnesses such as hypertension, diabetes and asthma. It is believed that in the near future, a better understanding of these interactions will allow us to use genetic and psychosocial information to determine who is at a greater risk for mood disorders, and which treatment methods are likely to be most effective for each individual.