Why do some people sail through life's difficulties, while others get mired in depression? A certain gene may explain such differences between people, a new study suggests.
Among the people in the study who had experienced highly stressful life events, those who had variants of the genes for a brain chemical called galanin were more likely to develop depression than those with similar experiences and normal galanin.
Galanin is a peptide widely found in the human nervous system, and is thought to be involved in regulating pain, waking and sleep, feeding, blood pressure and mood. A handful of studies have suggested that galanin has a role in stress and anxiety.
The findings suggest that brain's galanin system plays a significant role in the development of depression by making people more vulnerable to psychological stress, the researchers said in their study published today (March 24) in the journal Proceedings of the National Academy of Sciences. [Top 10 Controversial Psychiatric Disorders]
Exactly what causes people to develop depression is unknown, but it is believed that both environmental and genetic factors are involved in the condition.
Environmental factors include psychological stress, such as traumatic events and maltreatment early in childhood, or stress later in adulthood. Both have been shown to put people at high risk for depression.
"Nevertheless, not all people who suffer from these will be depressed," the researchers said. "The resilience or vulnerability to these stressors and thus depression, is likely to reside in our genes."
In the study, the researchers also found that the effects of the galanin system in the development of depression were greater among the people who were exposed to the most life stress. Among people with galanin gene variants, which should have put them at higher risk for depression, those who experienced a less stressful life fared better than those who led a stressful one.
This bolsters the idea that an interaction between the environment and genes is stronger than the effect of genes or the environment alone.
Most of the brain systems that have been studied in people with depression involve the neurotransmitters serotonin and noradrenalin, and it is thought that variations in the genes that code for these neurotransmitters and their receptors are partly involved in depression.
Most antidepressants today target these neurotransmitters, but the drugs are ineffective for many patients, suggesting that other brain mechanisms may be involved in this disease.
In the study, the researchers found the effect of the galanin system genes was stronger than the effect of the serotonin gene variants.
It's not clear how the galanin system fit in the development of depression, the researchers said, but the new results suggest that the galanin system should be explored as a target for developing new antidepressants.