Adoption may significantly decrease major depression risk among high-risk youth
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Among matched full and half siblings at high risk for major depression, those raised in adoptive homes had a significantly reduced risk compared with those raised in their home environment, according to findings of a high-risk home-reared and adopted-away co-sibling control study published in American Journal of Psychiatry.
“Major depression has recently been the subject of an intensive search to find the specific DNA variants that underlie genetic risk,” Kenneth S. Kendler, MD, of the Virginia Institute for Psychiatric and Behavioral Genetics and department of psychiatry at Virginia Commonwealth University, and colleagues wrote. “It has often been claimed that the familiality of major depression — which is substantial — results largely from genetic factors. Although this is an accurate summary of the twin studies of major depression, these studies only examine sources of resemblance among siblings and cannot provide insight into the causes of the equally important cross-generational transmission.”
Adoption studies have proved central in this area of psychiatric genetics. Four classic adoption studies of major depression found no evidence for environmental transmission of major depression risk from adoptive parents to adoptees; however, other studies suggested that growing up with parents who are depressed may be associated with numerous psychiatric effects.
Kendler and colleagues sought to determine the role of rearing environment in major depression etiology. They identified a Swedish national sample of 666 high-risk full sibships and 2,596 high-risk half sibships that contained at least one adopted-away sibling and one home-reared sibling and used national medical registries to assess major depression. They defined high risk as having at least one biological parent with major depression.
The researchers reported that after controlling for parental age at birth, sex and, for half siblings, history of major depression in the nonshared parent, major depression risk among the matched adopted compared with home-reared half and full siblings was reduced by 19% (95% CI, 10-38) and 23% (95% CI, 7-36), respectively. Relative educational status of the biological and adoptive parents did not influence the protective rearing effect; however, in both and full sibships, adoption’s protective effect disappeared when a stepsibling or adoptive parent had major depression or the adoptive home was disrupted by divorce or parental death.
“Our results further strengthen the evidence that high-quality rearing environments can meaningfully reduce rates of major depression in individuals at high familial risk,” the researchers wrote. “This finding supports efforts to improve the rearing environment in high-risk families as an approach to the primary prevention of major depression.”
In a related editorial, Myrna M. Weissman, PhD, of the departments of epidemiology and psychiatry at Vagelos College of Physicians and Surgeons and Mailman School of Public Health at Columbia University, commented on the nature vs. nurture debate that surrounds the etiology of depression.
“The answer remains ‘yes’: depression is nature and nurture, and the relative proportions, for which types of depression, are under study,” Weissman wrote. “In the meantime, there are actions to take that will improve both medical and psychiatric health. This latest study by Kendler and colleagues clearly points to the role of the nurturing environment.” – by Joe Gramigna
Disclosures: The study authors report no relevant financial disclosures. Weissman reports research funds from NIMH, the Sackler Foundation and the Templeton Foundation, as well as royalties from American Psychiatric Association Publishing, Oxford University Press and Perseus Press and royalties on the Social Adjustment Scale from Multihealth Systems.