Epigenetics is the study of heritable changes in gene function that may occur without modifying the gene sequence, often as a consequence of environmental exposures.
There are an increasing variety of epigenetic mechanisms that have been described, including the regulation of gene function via the methylation or demethylation of DNA.
Led by Drs. Michael Poulter and Hymie Anisman, the research team compared the brain tissues of those who had major depressive disorder and committed suicide to those from a control group who died suddenly, from heart attacks and other causes.
The researchers discovered that the genome was being chemically modified in individuals who have committed suicide as a result of major depression.
A process that is normally involved in regulating cell development did the chemical modification.
Poulter explained: "We have about 40,000 genes in every cell and the only reason a skin cell becomes a skin cell as opposed to a heart cell is because only a fraction of the genes are being expressed, and the other genes not being expressed are shut down by this genetic process of DNA methylation."
The researchers discovered that the rate of methylation in the suicide brains was almost ten times that of the control group.
They also found that the gene being shut down was a neurotransmitter receptor that plays a major role in regulating behavior.
Dr. John H. Krystal, Editor of Biological Psychiatry and affiliated with both Yale University School of Medicine and the VA Connecticut Healthcare System, said: "This is exciting new evidence that genetic and environmental factors may interact to produce specific and long-lasting modifications in brain circuits. Further, these modifications may shape the course of one's life in extremely important ways, including increasing the risk for major depressive disorder and perhaps suicide."
"The whole idea that the genome is so malleable in the brain is surprising, because brain cells don't divide. You get dealt your neurons at the start of life, so the idea that there are still epigenetic mechanisms going on is pretty unusual," added Poulter.
The authors indicated that the above findings open an entirely new avenue of research and potential therapeutic interventions.
The study was published in a recent issue of Biological Psychiatry.