"Having both this variant and a previously discovered gene means a person is 23 percent more likely to respond to the drug than people without either variation. Celexa (citalopram) is one of a widely used class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs), which also include Paxil, Prozac and Zoloft. "

"While these medications do appear to reduce depression for many who use them, their benefits vary widely among patients. The reasons behind that variance have remained unclear, experts say."

"But the new finding "suggests that we're going down the right path, although we're not there yet," said Dr. Gonzalo Laje, co-author of the study, which is published in the August issue of the "

". "We are better able to see how genetic variations help determine how a person may or may not respond to a certain medication. This is an advancement toward personalized medicine." "

"Laje is associate clinical investigator at the U.S. National Institute of Mental Health, which conducted the study. "

"However, the increased likelihood of response for people carrying the gene was relatively modest, indicating that only the sum of many genes -- most yet to be discovered -- will give scientists the whole story, experts said. "

""There's no one marker that's going to tell you whether you respond or not. It's a lot of markers, each one having a small effect," said Dr. Julio Licinio, chairman of psychiatry and behavioral sciences at the University of Miami Miller School of Medicine. "This is another building block, but it's not the whole story. In the future, as we put all these markers together, we may be able to develop a genetic panel to tell us whether a person is likely to respond to an SSRI or not.""

"Different people respond differently to different medications, and that's true for a wide variety of drugs, not just antidepressants. But with depression, especially, some patients respond happily to the first medication they try, while others have to go through a frustrating trial-and-error process before finding the right solution for their illness, if they find a solution at all."

"The Sequenced Treatment Alternatives to Relieve Depression (STAR*D) trial, the largest effectiveness study ever done on depression, examined the benefits of antidepressants in "real world" settings. "

"SSRIs are considered
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