Mom Can Increase Her Child's Risk of Depression via Nurture Alone

Science News - October 18, 2008

Some youngsters get depressed in the absence of any genetic legacy, a new investigation finds.

Researchers report that having a depressed mother substantially ups a teenager's likelihood of becoming depressed, even if he or she was adopted and shares no genes with the mother.

This finding provides the first direct evidence that purely environmental factors can promote depression in the children of depressed women, says a team led by psychologist Erin Tully of the University of Minnesota in Minneapolis.

A depressed father does not increase the risk of depression in adopted or nonadopted teens, the team reports in the September American Journal of Psychiatry.

Two other investigations, both published in the same journal, further emphasize nurture's role in depression, showing that successful treatment of depressed mothers spurs emotional gains in their depressed children.

"There is an environmental liability of maternal depression that cannot be accounted for by genes but that almost certainly interacts with genetic factors to create depression risk in children," Tully says.

Depression can impair a mother's parenting skills, cause marital conflict and disrupt a youngster's ties to peers and school - and these outcomes can in turn spread depression from mother to child, she suggests.

A growing number of studies demonstrate difficulties that depressed mothers have in interacting with their children, remarks psychiatrist John Markowitz of Columbia University. Tally's study "bolsters the evidence that maternal, more than paternal, depression meaningfully affects children through home life, not just heritability," he says.

Tully and her coworkers studied 568 adopted adolescents, most from Asian countries, 416 non-adopted adolescents and one or both parents of all the children. Nearly all parents and non-adopted kids were white, and all the families lived in Minnesota. Most adoptions occurred before age 1.

Psychiatric interviews with the parents and teenagers probed for current and past symptoms of major depression and other psychological conditions.

While living with a depressed mother boosted the mood disorder's prevalence in adopted teens, non-adopted teens with depressed mothers were even more likely to become depressed. Having a depressed mother also increased the rate of behavior problems in both groups.