Canadian researchers say a specific gene -- brain-derived neurotrophic factor -- is linked to suicidal behavior. Dr. James Kennedy, director of Centre for Addiction and Mental Health Neuroscience Research Department in Canada, said brain-derived neurotrophic factor is involved in the development of the nervous system. The scientists confirmed that among people with a psychiatric diagnosis, those with the methionine variation of the gene had a higher risk of suicidal behavior than those with the valine variation. The findings, published in the International Journal of Neuropsychopharmacology, included data from 3,352 people, of whom 1,202 had a history of suicidal behavior. About 90 percent of people who have died by suicide have at least one mental health disorder, the researchers noted. Of the studies reviewed, participants had schizophrenia, depression, bipolar disorder or general mood disorders. In each case, the researchers compared the genotypes of people who had attempted or completed suicide with those who were non-suicidal, Kennedy said. \"Our findings provide a small piece of the puzzle on what causes suicidal behavior,\" Kennedy said in a statement. \"When assessing a person\'s suicide risk, it\'s also important to consider environmental risk factors, such as early childhood or recent trauma, the use of addictive drugs or medications and other factors.\"