When children plunge into the darkness of depression, their growth hormone levels dip as well, researchers have discovered.

And now scientists have found something even more intriguing: Youngsters at familial risk of depression experience abnormally low growth hormone secretion, too.

This finding comes from scientists at the University of Pittsburgh School of Medicine’s department of psychiatry and at the Western Psychiatric Institute and Clinic in Pittsburgh. It is reported in the September Archives of General Psychiatry.

"The main implication, at least at this moment, is that this is more evidence that depression is a biological disorder, at least in part," Boris Birmaher, M.D., the study’s lead investigator, told Psychiatric News. "We think it is a combination of genetics and environment, like many illnesses. The implication is that these kids, even before they get depressed, already have a biological finding. . . .This helps the public, and actually insurance companies, know that we are talking about a biological disorder similar to other illnesses and that it should be treated as such."

Another of the study’s investigators, Neal Ryan, M.D., expressed a similar opinion in an interview: "We think this is a phenomenon that is . . .linked to something that is going on with the genetic liability or genetic and environmental liability for depression."

The finding makes one wonder whether there might be some cause-and-effect relationship between depression and growth hormone. However, this does not seem to be the case, Ryan said. For instance, he pointed out, it doesn’t look as though depression is stunting the growth of youngsters, and when depressed youngsters are given antidepressants, their growth hormone levels are not raised over the long term. Thus, there would be no sense in giving growth hormone therapy to youngsters who are depressed, he said.

The finding also makes one wonder whether suppressed growth hormone levels might be used to predict a bout of major depression or as a diagnostic tool. Yet when asked about this possibility, Birmaher replied: "We are very cautious about saying whether we will be able to use this as a test; it is too early to say."

Ryan expressed a similar outlook. "It is unlikely that this will be a clinical test." Whereas the growth hormone test is strong enough to separate depression-prone youngsters from nondepression-prone youngsters to be scientifically interesting, it is not powerful enough to separate the two groups to be clinically valuable, he said.

Sixty-four children and adolescents with at least one first-degree relative and at least one second-degree relative with a history of childhood-onset depression, recurrent depression, bipolar disorder, or psychotic depression were recruited for a study through advertisements or through parents who attended a mood disorders clinic. The 64 youngsters were then matched with 55 healthy children at low familial risk for depression.

Subjects then entered a child sleep lab where a catheter was placed in a vein in each child, but no blood was drawn. The next morning, blood samples were obtained from the subjects to measure their baseline levels of growth hormone. After that they were given intravenous injections of growth hormone–releasing hormone (GHRH), and once again blood samples were collected, this time to measure growth hormone response to GHRH stimulation. The researchers then compared growth hormone levels before GHRH stimulation in high-risk subjects with those in the low-risk subjects, and growth hormone levels after GHRH stimulation in the high-risk subjects with those in the low-risk subjects.

Growth hormone levels before GHRH stimulation were comparable in the high-risk group and in the low-risk group, the investigators found. However, whereas both high-risk subjects and low-risk subjects showed increased growth hormone secretion after GHRH administration, the magnitude of the increase was markedly less in the high-risk group. Even after adjusting the results for age, sex, and other factors that might have distorted the results, the high-risk group still showed significantly lower growth hormone levels than the low-risk group did.

"The results of this study," the researchers reported, "suggest that decreased growth hormone response to GHRH may be a trait marker for major depressive disorder, and the mechanisms that control the secretion of growth hormone may be already altered before the first depressive episode."

Birmaher and his team will next study these mechanisms in their high-risk subjects, and unmasking the mechanisms, he said, "will help us understand the biology of depression."