Suicides always leave behind sad and tough questions. One big one is whether those who commit suicide have faulty genes.
It turns out that although they may have normal genes, child abuse may still have left its mark on the DNA in the brains of some, new research suggests.
About 30,000 people die by suicide each year in America. While scientists also think other factors are involved with suicide, this new finding raises the possibility that detecting or even wiping out these markings could help prevent people from killing themselves.
The researchers investigated the brains of 13 men who committed suicide. All of them had experienced child abuse. These were compared with the brains of 11 men who died of sudden unexpected causes and had no history of child abuse.
The scientists focused on a set of genes that are the blueprints for ribosomal RNA, or rRNA. These molecules help synthesize proteins in cells. Protein synthesis is critical for learning, memory and the building of new connections in the brain, among other things.
The genetic sequences for the rRNA were identical in both groups of men. However, there were differences when it came to molecules latched onto these genes. These so-called "epigenetic markings" can bind up a gene, essentially turning it off.
In the hippocampus, a brain region key to controlling responses to stress, the researchers found the rRNA genes in suicides were "hypermethylated," possessing far higher levels of these markings than normal. This in turn would have reduced levels of protein synthesis.
"Protein synthesis is required for many brain functions, and subtle differences at times of distress might affect connections in the brain that normally protect us from suicidal behavior," said researcher Moshe Szyf, an epigeneticist at McGill University in Montreal.
While genes remain unchanged throughout a person's life save for exceptional circumstances, epigenetic markings can be influenced by the environment, especially early in life. It is possible that after traumatic events, chemicals released by pain or strong emotion could trigger a cascade of events that change these markings in the brain, as witnessed in these suicides.
Neuroscientist Yogesh Dwivedi at the University of Illinois at Chicago, who did not participate in this study, said, "This is the very first time anyone has reported that genes in the brain can be regulated by environmental factors in cases of suicide. This is very exciting work and promises a new era of research in suicide."
Of course, there are many other factors linked with suicide.
"The presence of mental illness plays by far the largest role in risk for suicide, in more than 90 percent of cases," said researcher Gustavo Turecki, a psychiatrist and neuroscientist at McGill. "And males die by suicides much more frequently than women — here in Canada, it's about a 4 to 1 ratio. Then you have personality traits such as impulsivity and aggression playing a role, as well as substance abuse, and recent traumatic events, and social factors such as the level of access to support services, and of course genetic factors that may increase an individual's predisposition to suicide."
"What's nice about our new work is that it helps understand how the environment interacts with a person's biology to increase the risk for suicide," Turecki added.
Dwivedi added that while many factors can play a role in suicide, "so far you cannot directly relate any of those factors to how likely [it is that] a person will commit suicide. It will be very important to see whether this epigenetic work can help answer such a question."
The big questions now, Szyf said, "are whether scientists could detect similar changes in blood DNA — which could lead to diagnostic tests — and whether we could design interventions to erase these differences in epigenetic markings."
"Epigenetic marks are reversible even in adults," Szyf told LiveScience.
In light of this preliminary research, far more brains need to be analyzed, the researchers acknowledged. In addition to also investigating women who killed themselves, Szyf noted, it would be especially interesting to look for any brain differences among suicides who had a documented history of child abuse and others who did not.
"It would also be very interesting to look at populations with a high incidence of suicide, such as the aboriginal population in Canada," he added. Investigating other genes or different regions of the brain for epigenetic marks could prove vital as well.
The scientists detailed their findings in the May 6 issue of the online journal PLoS ONE.
The researchers were funded by grants from the National Institutes of Health, the Human Frontier Science Program and the Canadian Institutes for Health Research.