Some youngsters suffer from depression 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.

Having a depressed father does not increase depression susceptibility in either adopted or non-adopted teens, Tully and her colleagues report in the September American Journal of Psychiatry.

Two other investigations, both published in the same journal, further emphasize nurture’s role in depression. They show that successful treatment of depressed mothers — either with medication or psychotherapy — 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, Tully suggests.

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

Tully and her coworkers studied 568 adopted adolescents, most from Asian countries, 416 non-adopted adolescents and one or both parents of all 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 of 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 were even more likely to become depressed themselves. For non-adopted teens, genetic influences may amplify as the detrimental effects of environmental factors, the researchers suggest.

Having a depressed mother also increased the rate of delinquency and other behavior problems in both adopted and non-adopted teens.

Neither adopted nor non-adopted teens’ emotional problems triggered depression in their parents, in Tully’s view. Depression in mothers initially appeared around the time a child was born and about one year before a child’s birth for fathers. Still, the researchers note that teens’ travails may have influenced further bouts of depression in their parents.

Mental-health backgrounds of adoptees’ birth parents were unavailable. But based on the results, Tully doubts that adoptees with depressed adoptive mothers face any greater genetic risk of depression from their biological parents than do adoptees with non-depressed adoptive mothers.

Another new study of parents and non-adopted children further elaborates on the role of family environment in depression. Children dealing with symptoms of depression and anxiety showed noticeable emotional advances after their mothers’ depression had cleared up with antidepressant medication, reports a team led by psychologist Myrna Weissman of Columbia University.

Children benefited most if their mothers had responded to treatment within three months. Considerable improvement also occurred in children whose mothers’ depression eased within one year of starting treatment.

In Weissman’s study, 70 of 123 depressed women recovered from the mood disorder within one year of starting treatment. Most received antidepressant medication until they met criteria for remission. A few who did not respond to medication received cognitive-behavioral psychotherapy.

At the start of treatment, about one-third of participants had a child with depression, anxiety or behavior problems.

Successful psychotherapy for depressed mothers also aids children’s emotional health, say psychiatrist Holly Swartz of the University of Pittsburgh and her colleagues. Her team studied 26 depressed mothers who received nine weekly sessions of interpersonal psychotherapy, and 21 depressed mothers who received referrals to local mental-health clinics. At three- and nine-month follow-ups, the depression had declined much more sharply in the mothers who had received interpersonal psychotherapy.

Interpersonal psychotherapy focuses on motivating patients to participate in treatment and on identifying strategies that they can use to interact more effectively with family members.

All mothers were recruited from a psychiatric center where their school-age children were receiving treatment for depression.

Most women assigned to interpersonal psychotherapy improved within three months. Their children’s depression substantially lifted at the nine-month follow-up, suggesting that maternal changes had sparked kids’ improvement.

Since mothers often take primary responsibility for child rearing, depressed fathers may influence depression in their non-adopted children mainly through shared genes, Tully suggests. This possibility deserves further scientific scrutiny, she says.

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