Researchers have provided evidence that may explain why some people respond better to depression drugs (search) than others.

If confirmed, the finding could help patients get prescriptions for antidepressant medications (search) that suit them best.

Depression is extremely common. In the U.S., it affects almost 19 million adults annually, according to the National Institute of Mental Health.

A serious illness, depression is also considered to be highly treatable. However, it can take some experimentation to find the right prescription for each patient, since people may respond differently to the drugs.

To streamline the process, researchers are studying the role of genetics in the response of patients to antidepressant drugs. Their goal is to find gene patterns that predict which drugs work best for different groups of patients.

For instance, it was reported earlier this month that a gene mutation prevented some people from responding well to antidepressants known as selective serotonin reuptake inhibitors (SSRIs), such as Prozac. (search)

Now, researchers are providing details of more genetic insights.

A new study focuses on genes that govern production of corticotrophin-releasing hormone (CRH), which affects depression and anxiety. Variants of the CRH gene were studied by researchers including Julio Licinio, a psychiatry and biobehavioral sciences professor at UCLA's medical school.

Licinio and colleagues analyzed the genes of 80 Mexican-American adults in the Los Angeles area. Of that group, 54 had test scores that indicated symptoms of high anxiety. All the subjects had major depression.

Participants were assigned to take Prozac or another depression drug, Norpramin, for eight weeks. In response to the treatment, those with a certain variant of the CRH gene had 70 percent less anxiety and 31 percent less depression than those without the gene variant.

However, those results were only true for participants who were highly anxious as well as depressed. The findings need to be confirmed and tested in a larger, more diverse study, say the researchers.

Their study appears in Molecular Psychiatry's December edition.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Licinio, J. Molecular Psychiatry, December 2004; vol 9: pp 1075-1082. National Institute of Mental Health. WebMD Medical News: "Gene Mutation Linked to Risk of Depression." News release, UCLA.