TUCSON, Ariz., Feb 18, 2002 (United Press International via COMTEX) -- A University of Arizona study released Monday supports current belief that serotonin closely regulates mood and the notion people with certain genetic markers may be more vulnerable to depression.
"It's been assumed that depression has a genetic component and the study says there are genetic vulnerabilities to experiencing depression, although we don't know what exactly causes depression," Dr. Francisco Moreno, of the Department of Psychiatry in the College of Medicine at the University of Arizona Health Sciences Center in Tucson, told United Press International.
"The study also found that a temporary alteration of serotonin activity can be obtained by lowering the blood levels of tryptophan -- an amino acid needed for the synthesis of serotonin."
The study is published in Molecular Psychiatry & Pharmacogenomies Journal. In several studies, acute depletion of tryptophan causes depressive symptoms in some but not all patients who had at least one episode of major depression, Moreno said.
This study investigated the relationship between depressive symptoms during tryptophan depletion and the presence of a variation of the gene encoding for a protein that transports sertonin into neurons.
"We looked at the gene that blocks the transporter of serotonin into the nerve cells and found it happens when a person is more depressive," Moreno said. "While we used one gene marker there probably are a number of genes involved with depression vulnerabilities."
Forty-three subjects who had improved from a major depressive episode underwent tryptophan depletion and were invited to participate in the genetic testing. Depressive symptoms were measured with the 25-item Hamilton Depression Rating Scale.
During tryptopan depletion, subjects experienced different degrees of depressive responses, but there was a clear indication that people whose genes predicted increased serotonin transporter activity had a lot more depression than people whose genes predicted less activity.
"It's like smoking, some people have a genetic predisposition to cancer and some don't, but those who smoke and have the genetic trait will have a better chance of getting cancer," Moreno said. "There are also different variables for depression besides genes, for example, there can be previous environmental exposures to trauma."
In the future, we might be able to identify people with a potential or a vector to experience depression, Moreno said.
"We would be able to tell who is at a higher risk for depression, if we knew who to treat, whether it's treating sertonin levels or something else, we could see the red flags for depression better," he said.
Serotonin acts as a chemical messenger or neurotransmitter in the central nervous system and appears to affect sleep, appetite and mood. Serotonin levels in the brain can be increased by the ingestion of tryptophan, found most in milk and turkey.
"It's an interesting study -- combining the genetic marker with diet or the use of tryptopan -- but a limitation of the study, which it mentions, is the small number of subjects," Dr. Frederick Moeller, an associate professor of psychiatry at the University of Texas Medical School at Houston, told UPI. "But it's a good preliminary study that should be followed up with a larger sample."
Moeller warned the study should not be interpreted that increasing amounts of tryptophan via supplements could be used to avoid depression. There is no scientific link between tryptophan and depression and the U.S. Food and Drug Administration has removed it from power drinks and other supplements.
In 1973, Canada reported 11 cases of eosinophilia-myalgia syndrome, 10 of which were among victims who purchased supplements in the United States that contained L-tryptophan.
"EMS is a serious and often fatal disorder linked to L-tryptophan use and, in one case, possibly to use of the amino acid supplement lysine," said Dr. Timothy Gorski, associate clinical professor of obstetrics and gynecology at the University of North Texas Health Science Center and an associate editor for the Scientific Review of Alternative Medicine.
"In 1990, after a 1989 outbreak of EMS in the United States in which at least 27 died and some 1,500 were affected, the FDA pulled L-tryptophan off of store shelves," Gorski said. "The lesson in this story is that, while L-tryptophan is an essential amino acid, it is certainly not ordinarily ingested in the amounts provided by some supplements."
A paper released by the FDA in February 2001 said: "Numerous trace level impurities have been identified in the L-tryptophan implicated in many of the EMS cases." The report added the role, if any, of these impurities in EMS was unclear.
FDA said: "At the present time, an import alert remains in force which limits the importation of L-tryptophan into the United States, except if it is intended for an exempted use. FDA has provided for the use of manufactured L-tryptophan for special dietary purposes."
L-tryptophan is legally used in such things as infant formulas, enteral products and parenteral drug products. It also may be added as a nutrient to special dietary foods, which are intended for use under medical supervision.
(Reporting by Alex Cukan in Albany, N.Y.)
Copyright 2002 by United Press International.