(Reuters)
Updated: 2007-08-01 18:43

Ideally, Laje would like to be able to find enough gene variants to predict when a patient is 95 percent more likely to benefit.

Celexa is in a class of drugs called SSRIs, or selective serotonin reuptake inhibitors.

Researchers studied DNA samples collected in the $35 million, seven-year Sequenced Treatment Alternatives to Relative Depression, or STAR*D, a study paid for by the National Institute of Mental Health.

Earlier findings from this study found Celexa sent 37 percent of patients who took it into remission.

In the latest study, researchers examined genetic material from 1,816 patients, comparing data from those who responded to Celexa and those who didn't.

They found people with a variation in the GRIK4 gene were more likely to respond to the drug, especially when they also had a variation of the HTR2A gene.

Prior studies have shown variations in the HTR2A gene -- which makes a protein related to the chemical messenger serotonin -- play a role in a patient's response to Celexa.

The GRIK4 gene makes a protein that is involved with the glutamate system, which also has been linked with depression.

Researchers said the findings are building a better picture of the biological mechanisms that underlie depression, a disease that affects about 121 million people worldwide, according to the World Health Organization.

In the United States, an estimated 21 million adults, or 9.5 percent of the population, have depression at some point. It is the leading cause of suicide.

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