September 30, 2007
Genetic Variants Increase Suicide Risk On SSRI Antidepressant

There's been controversy on whether those who take selective serotonin reuptake inhibitor (SSRI) antidepressants are at greater risk of thinking suicidal thoughts. It is a difficult effect to tease out since people depressed enough to take SSRIs are already at greater risk of depression and some of them probably become less at risk of suicide because SSRIs brighten their mood. But maybe others react to SSRIs by becoming more suicidal. Well, genetic testing might have allowed some scientists to discover who will be at greater risk of suicidal thoughts as a result of taking an SSRI. People taking the SSRI drug citalopram who have certain variants of glutamate receptor genes are at much higher risk of suicide thoughts.

Specific variations in two genes are linked to suicidal thinking that sometimes occurs in people taking the most commonly prescribed class of antidepressants, according to a large study led by scientists at the National Institutes of Health’s (NIH) National Institute of Mental Health (NIMH). Depending on the particular mix inherited, these versions increased the likelihood of such thoughts from 2- to15-fold, the study found. About 1 percent of adult patients were deemed to be at high genetic risk, 41 percent at elevated risk and 58 percent at lower risk.

If confirmed, the findings may hold promise for genetic testing, as more such markers are identified.

The "If confirmed" is important. They looked at many genes and so a false positive just by chance is possible.

Risk increased proportionately if a participant had two, as opposed to just one of the suspect versions. Both genes code for components of the brain’s glutamate chemical messenger system, which recent studies suggest is involved in the antidepressant response.

Overall, about 6 percent of 1,915 patients with depression reported that they started to have suicidal thoughts while taking an antidepressant. This rate soared to 36 percent among the few patients with both of the suspect gene versions; 59 percent of the patients who had suicidal thoughts had at least one of the versions.

Francis J. McMahon, M.D., Gonzalo Laje, M.D., NIMH Mood and Anxiety Disorders Program, and colleagues at the National Human Genome Research Institute (NHGRI), Mount Sinai School of Medicine, and the University of Texas Southwestern Medical Center, report on their findings in the October, 2007 issue of The American Journal of Psychiatry.

We are well within 10 years of widespread use of genetic testing when choosing between drugs and making other treatment decisions. Clinical practice will take a big turn when genetic tests can predict which drugs will cause which side effects in each patient.

The researchers found that certain versions of two genes that code for glutamate receptors – the receiving stations for the neurotransmitter’s chemical messages – were more prevalent in patients with suicidal thinking. How the newly identified versions affect the workings of glutamate receptors to confer increased risk remains to be discovered. It’s also not yet known whether the findings generalize to other antidepressants.

One percent of the study participants had a version of the kainate receptor gene, GRIK2, that increased the odds for suicidal thinking more than 8-fold. Forty-one percent of participants had a version of the AMPA receptor gene, GRIA3, that raised the odds nearly 2-fold. About one-half of 1 percent of participants had both high risk gene versions, boosting the odds 15 fold – but this was the case for only 11 participants, of whom four developed suicidal thinking.

The size of the observed effects makes it likely that their finding is real. It is the sort of result that could be confirmed pretty quickly with sufficient funding.

A discovery like this one is not just useful for making drug choices. It also provides clues about what causes people to become suicidal. A better understanding of the mechanisms which cause suicidal thoughts will lead to ways to stop suicidal thoughts.

Share |      Randall Parker, 2007 September 30 09:52 PM  Brain Depression

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