The Johns Hopkins researchers looked at how a group of chemicals known as methyls affect the gene SKA2, which modifies how the brain reacts to stress hormones.

If the gene’s function is impaired by a chemical change, someone who is stressed won't be able to shut down the effect of the stress hormone, which would be like having a faulty brake pad in a car for the fear center of the brain, worsening the impact of even everyday stresses.

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Researchers studied about 150 postmortem brain samples of healthy people and those with mental illness, including some who had committed suicide. They found that those who died by suicide had significantly higher levels of the chemical that altered the SKA2 gene. As a result of the gene’s modification, it was not able to “switch off” the effect of the stress hormone.

The researchers then tested sets of blood samples from more than 325 participants in the Johns Hopkins Center for Prevention Research study to see whether they could determine those who were at greater risk of suicide by the same biomarker.

They were able to guess with 80 to 90 percent accuracy whether a person had thoughts of suicide or made an attempt by looking at the single gene, while accounting for age, gender and levels of stress or anxiety.

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Zachary Kaminsky, an assistant professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine who led the study, said that while the biomarker indicates a person’s vulnerability to stress and anxiety, it does not make a person destined to experience suicidal thoughts and could equally show a person’s resilience.

It’s like a person trying to cross the street, Kaminsky said. It doesn’t make you destined to be hit, but might encourage you to be a more aware pedestrian. The stress hormone cortisol has a role in performing both daily tasks and responding to extreme situations.

“It helps you get up in the morning, it helps you cross the road, and it helps you run away from a lion,” Kaminsky said.

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There are scales of severity and varying spectrums of contemplating, planning and attempting suicide, and Kaminsky said that the biomarker may not be a determining test for all cases. The study may have just determined the chemical marker of how a person is affected by stress and anxiety.

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Suicide is the 10th-leading cause of death for Americans, according to the National Action Alliance for Suicide Prevention. The organization aims to reduce the national suicide rate by 20 percent within five years through research and identifying those at greatest risk.

“Suicide is complex and many factors affect a person’s risk, including biological, psychological and social factors, as well as access to lethal means,” said Jill Harkavy-Friedman, vice president of research at the American Foundation for Suicide Prevention.

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She said suicide rates in the United States have remained stable over the past few decades, with slight increases and decreases.

She sees the Johns Hopkins study as part of an increasing body of research investigating genetics as a factor, helping to better assess long-term and immediate risk and to eventually reduce rates of suicide.

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The biomarker could help doctors determine a patient’s risk, but assessment still needs to be individually based, Harkavy-Friedman emphasized.

For example, “you wouldn't just look at one cholesterol level, you would look at diet, family history and what they ate that day,” she said. “It’s an important step on the right path.”