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Nature, Nurture Team up in Depression Equation
> 1/17/2008 10:04:26 AM

Nearly every one of the endless set of human variables has been drawn into the nature vs. nurture debate. Trends in academic performance, physical prowess, subtance abuse, personal relationships, political affiliations: are these inborn, immutable properties that can only be further magnified and coaxed along their natural way by life experience, or can our environments actually create them where they wouldn't otherwise exist?

Drawing on fascinating data to make conclusions, researchers have observed that neglectful or abusive home lives do more than their share of the work in creating states of chronic depression, especially when combined with a physiological propensity toward the disorder. The two compliment each other in very fundamental ways. Perhaps most interestingly, recent studies seem to contradict the general assumption that genetics trump environmental factors in determining the prevalence of depressive disorders, suggesting that stressful life events may play a larger role than brain chemistry in some cases.

Genetic predispositons (which occur in at least 20% of the general population) almost always exist, and cases of deep chronic depression (as opposed to post-traumatic stress disorder) arising explicitly from major life events are the exception to the general rule. But they do exist. In fact, researchers have devised a simple formula to estimate the risk of depression in those fitting the genetic model: in long-term studies, 8 in 10 patients with genetic dopamine deficiencies developed depression if they experienced three or more negative life events within a year's time. A more revelatory fact applies to the 25% of the population who carry opposing genes that foster a resilience to depression: when faced with the same string of three or more negative events, 30% will develop clinical depression. This observation furthers the argument that "nurture," or at least the presence of confounding life circumstances, can create depression even when the patient's genetic makeup does not leave them particularly sensitive to it.

The subjects of the most recent related study were drawn from perhaps the likeliest source of horror stories regarding mental illness and family dysfunction: adolescent males in juvenile detention. After interviewing the 177 subjects, researchers determined that the two factors most likely, in combination, to produce a depressive adolescent were inherited dopamine transporter gene irregularities and a sense of maternal rejection. Unreciprocrated love for one's mother has also been coincidentally linked to drug use, violent crime and abusive parenting. Researchers have long drawn links between dopamine deficiencies, ADHD, alcoholism and nearly every mood disorder, but this study highlights how three particular polymorphisms of the dopamine transmitter gene facilitate depression and suicidal ideation and intensify the resentment born of perceived mistreatment at the hands of one's parents.

The larger point: certain genotype variations appear to leave patients predisposed to depressive disorders, and they lead to depression in a majority of cases when combined with problematic environments. In identifying at-risk individuals as early as possible, experts could help to minimize the risks they face through either social interventions or medical procedures designed to counter dopamine transporter irregularities. Abusive and neglectful parents would most likely not dramatically modify their own behaviors on the advice of experimental psychiatrists, but a knowledge of the problem's roots is the first step on the way to more viable solutions.

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