WEDNESDAY, Feb. 16 (HealthDay News) -- Children who carry a variant of a so-called "resilience gene" get along much better with their troubled parents -- those who have substance abuse, mental health or criminal problems -- than those without the gene, a new study suggests.

Assessing 226 children aged 9 to 17, researchers at Duke University Medical Center said the findings could explain genetically why some children in problematic families manage to maintain enjoyable relationships with their parents while others are blighted by the experience.

The scientists tested the premise that opioids -- naturally occurring "feel-good" brain chemicals -- help moderate social interactions in humans. Youngsters with the variant of the mu-opioid gene receptor were more influenced by the opioids than typical children, prodding them to create better parent-child relationships despite strife, lead author William Copeland said.

"Part of the reason we find relationships so positive and reinforcing is there are endogenous opioids released that affect that," said Copeland, associate professor of psychiatry and behavioral sciences at Duke. "People who have that variant experience more of that reward."

When these children are in a negative home environment, "there's almost a withdrawal effect -- so they do what they can to elicit positive interactions from their parents," Copeland said. "It's like the brain is saying, 'I used to feel this very positive state, now I'm not experiencing that anymore and I'd like to get back to that.'"

The study is reported in the Feb. 16 online issue of the journal Neuropsychopharmacology.

The mu-opioid receptor gene, known as OPRM1, has previously been associated with social behaviors in mice and rhesus monkeys. In Copeland's study, participants underwent DNA tests and answered questions about their enjoyment of parent-child activities, arguments and separation anxiety symptoms over the prior three months.

A measurement of "parental impairment" was derived by choosing difficulties such as substance abuse, mental health conditions or criminal problems that would predispose parents to be inconsistent, impaired or unavailable for relationships with their children.

More than 59 percent of the children had a parent reporting at least one of these difficulties, according to the study. About one-third carried the OPRM1 gene variant.

Over a three-month period, children with the variant who lived in problematic households reported significantly fewer arguments and far more enjoyable interactions with their parents than did children without it, although no such association was found in children who came from stable homes.

"I am generally a skeptic about being able to find these [genetic] markers," Copeland said, noting surprise at his results. "When we make a hypothesis, by no means do we know what the answer is going to be. Otherwise we wouldn't have asked the question."

Robert Plomin, a research professor and deputy director of the Social, Genetic and Developmental Psychiatry Center at King's College London in England, said it was interesting to learn that the opioid gene variant is associated with parent-child relationships only when parents have problems.

"Although it's a plausible finding, we need to be wary because the [study] sample is relatively small, especially when the sample is divided by whether or not parents had problems," Plomin said. "Reports of simple associations such as a gene variant associated with parent-child relations have been notoriously difficult to replicate and this is especially the case when an interaction is reported . . . only for a particular subsample."

More information

Learn more about behavioral genetics from the Human Genome Project.