Some carry genes that magnify parenting’s influence

Why do some children of mean, neglectful or downright toxic parents become rotten human beings themselves, while their siblings thrive cheerfully? And why do certain offspring of loving, attentive parents grow into well-adjusted adulthood while their siblings become sour misanthropes? In short, why does good parenting only sometimes produce good kids, and bad parenting only sometimes produce bad kids?

The answer may lie in the genes. Specifically, the almost-famous 5-HTTLPR serotonin transporter-promoter gene, which governs the activity of the mood chemical serotonin in the brain and essentially comes in three varieties. About 1 in 5 children are born with a variant that, according to past studies, makes them highly sensitive to the effects of neglectful, insensitive or abusive parents.

A study published this week in the journal Translational Psychiatry breaks new ground in asking whether those same children might also be super-sensitive to the effects of good parenting. In three different experiments, researchers tested 1,874 children between the ages of 8 and 16 to determine which variation of the 5-HTTLPR allele they had, what their overall mood state was, and what quality of parenting they had.

After crunching the numbers, researchers found that, when blessed with especially warm and supportive parents, the kids with the same 5-HTTLPR variation that predisposed them to be sensitive to poor parenting were disproportionately likely to be very happy and well-adjusted.

In other words, most kids are equipped with genes that make them somewhat impervious to the quality of the parenting they get. But the roughly 1 in 5 kids with the homozygous short allele of the 5-HTTLPR serotonin transporter gene? They are far more captive--for better or worse--to the quality of parenting they get.

In the long-running nature-nurture debate, genetic research is bringing the contributions of nature into clearer focus. But that same research is making clear that victory will be possible for neither side: When it comes to shaping a person’s behavior and personality, genes interact with environment. For certain behavioral traits--including vulnerability to mental illness--nature can be a powerful primer, but environmental factors--including childhood adversity--must ignite the spark that makes it happen.

Just as some parents are especially bad--or good--some genes make a kid especially sensitive--or not--to them.