Rearing Environment has Large Impact on Major Depression Risk

Kenneth Kendler, MD

If an adoptive parent suffers from major depression, the adopted child has a higher risk for developing depression, according to a new study based in Sweden.

A team, led by Kenneth S. Kendler, MD, Virginia Institute for Psychiatric and Behavioral Genetics at Virginia Commonwealth University, attempted to clarify the role of rearing environment in the etiology of major depression.

In the study, the investigators identified 666 high-risk full sibships and 2596 half sibships containing at least 1 home-reared and 1 adopted-away sibling in a Swedish National Sample.

The investigators defined individuals as high risk for major depression if they had at least 1 biological parent with major depression. Major depression was assessed from national medical registries.

After controlling for sex, parental age at birth, and, for half siblings, history of major depression in the nonshared parent, the investigators found the risk of major depression in the matched adopted compared with home-reared full and half siblings was reduced by 23% (95% CI, 7-36) and 19% (95% CI, 10-38), respectively.

The protective rearing effect was not influenced by the relative education status of either the biological parents or the adoptive parents.

However, for both full and half sibships, the protective effect of adoptions disappeared when an adoptive parent or stepsibling had major depression, or the adoptive home was disrupted by parental death or divorce.

In a separate study, investigators from the UK discovered perinatal depression in mothers is associated with a greater risk of their offspring reporting psychotic experiences by 18 years old.

The study, believed to be the first to associate maternal perinatal depressive symptoms and adult offspring psychosis, indicates common development mechanisms might be driving genetic psychiatric risk—and stresses the need for increased mental health monitoring of pregnant and postnatal women.

A team, led by Ramya Srinivasan, BMBCh, of the University College London, conducted a longitudinal study of data from the Avon Longitudinal Study of Parents and Children (ASPLAC), a 14,541-participant birth cohort of pregnant women with an estimated delivery date between April 1991 and December 1992.

In the ASPLAC study, investigators had measured depression through the Edinburgh Postnatal Depression Scale (EPDS). Srinivasan and colleagues gauged observed participants’ offspring for psychotic experiences at 18 years with the Psychosis-Like Symptom Interview. They used logistic regression to assess the link between maternal depression—both antenatal and postnatal—and early adult offspring psychotic experiences.

Maternal antenatal depressive symptoms were associated with an unadjusted 38% increased risk of offspring adult psychotic experiences (uOR, 1.38; 95% CI, 1.18-1.61; P = .0001), and a 26% increased risk when adjusted for confounders (OR, 1.26; 95% CI, 1.06-1.49; P = .0074).

Both offspring depression (OR 1.18; 95% CI, 1.03-1.34; P = .016) and psychotic experiences (OR, 1.32; 95% CI, 1.16-1.51; P <.0001) at 18 years were associated with maternal antenatal depressive symptoms, per five-point increase in EPDS scores. That said, investigators found no evidence of differing strength in either’s association with maternal antenatal depression.

Ultimately, the rearing environment has a meaningful impact reducing the risk of major depression, with the effect likely mediated both by parental depression and the continuity or disruption of the home environment.

“In matched full and half sibships at high risk for major depression, compared with individuals raised in their home environment, those reared in adoptive homes (homes selected in Sweden for their high-quality rearing environment) had a significantly reduced risk for major depression,” the authors wrote. “This protective effect disappeared if an adoptive parent had major depression or if the adoptive home experienced parental death or divorce during childhood/adolescence.”

The study, “The Rearing Environment and Risk for Major Depression: A Swedish National High-Risk Home-Reared and Adopted-Away Co-Sibling Control Study,” was published online in The American Journal of Psychiatry.