March 17, 2006 — Scientists may have a new clue about why some people respond better to a particular antidepressant than others.

A variation on a specific gene may make a difference, according to a study in The American Journal of Human Genetics‘ early online edition.

“Many patients can expect their condition to improve with antidepressant treatment,” write the researchers. “But only a minority experience full remission, and individual outcomes differ across medications,” they continue.

Genetics could contribute to those differences, write the researchers. They included Francis McMahon, MD, of the National Institute of Mental Health (NIMH). But McMahon and colleagues haven’t totally solved the riddle — at least, not yet.

Digging Through DNA

McMahon’s team focused on 68 genes tied to serotonin, a brain chemical targeted by several antidepressants.

Then, the scientists dug deeper. They analyzed variations of those genes and screened the genes of 1,953 depression patients who took the antidepressant Celexa in a study.

One particular gene variation on a single gene was more common in study participants who responded to Celexa. People with that gene variation were 18% less likely not to respond to Celexa — a “modest” difference, write McMahon and colleagues.

The gene variation was also six times more common in whites than in blacks in the study. Whites — who accounted for most study participants — were more likely to respond to Celexa than blacks, the researchers also note.

Complexity of Genes

Other genes could be involved, and more research is needed, the researchers note.

A person’s genetic coding is long and complicated. Imagine it as a lengthy book, flipped open to the section you think has the content you’re seeking. Then imagine checking for subtle differences in the fine print of a few paragraphs — without analyzing earlier or later pages — in nearly 2,000 unique editions of the book.

On top of that, genetic coding is just part of the picture. Social and personal influences may also play a role, the researchers note.

Depression is common and often treatable. In any given year, 19 million U.S. adults have depression, according to the National Institute of Mental Health.

A variety of depression treatments are available, including antidepressants and counseling. Asking for help is the first step to finding a solution.