New Clues About a Depression Gene
Study: Brain's Wiring for Mood Regulation May Be Affected
May 9, 2005 -- Hot on the trail of the genetic influences on depression, researchers may have found a new clue about one particular gene.
The gene -- called 5-HTT (the serotonin transporter gene) -- may be one of several genes that affect susceptibility to depression. Serotonin, a brain chemical messenger, has been implicated in depression. When levels get too low, you get depressed.
However, a variation in this gene doesn't seem to doom anyone to depression by itself. If it did, Daniel Weinberger, MD, and colleagues might have had a harder time with their study. The results appear in Nature Neuroscience's online edition.
The exact causes of depression are not known. Both genetic and environmental factors may play a role.
For the public, perhaps the most important thing to know about depression is that it's treatable. It's also a serious, widespread illness tied to other health risks. Nearly 19 million American adults per year have depression, according to the National Institute of Mental Health (NIMH).
Weinberger's study only included people who were not mentally ill; some had a different version of the 5-HTT gene, which has been linked to increased vulnerability to depression in response to life's stresses.
A total of 114 people got brain scans with magnetic resonance imaging (MRI). Then, 94 participants got a brain scan while viewing images of angry or fearful faces. That scan was intended to show the brain's fear circuitry in action.
People with short versions of the 5-HTT gene had decreased brain regions critical for the extinction of negative emotions, says the study. They also had weaker connections in this region; the altered circuitry may increase their susceptibility for depression.
Key Brain Areas for Depression
The difference in brain regions was seen in two parts of the brain. One was the amygdala, a fear-processing center deep inside the brain. The other was the cingulate, an emotion-dampening center located near the front of the brain.
"The brain handles information much like an orchestra," says Weinberger in a news release. "So we asked questions akin to, 'Are the violin and the clarinet playing the same tune and to what extent might this gene account for it?'"
Almost 30% of the variation in participants' scores for harm avoidance -- an inherited temperamental trait associated with depression and anxiety -- was explained by how well the mood-regulating circuitry was connected, says an NIHM news release.