Potentially, testing for CYP450 gene variations could provide benefit by guiding the initial choice or dose of SSRI for patients with depression. The U.S. Food and Drug Administration recently approved a CYP450 test that may help individualize drug treatment for a wide variety of commonly prescribed drugs, including SSRIs. Specific applications of this test, however, require validation.
The EGAPP Working Group based their recommendation on a commissioned systematic review of the research evidence on CYP450 gene testing by the U.S. Agency for Healthcare Research and Quality. Other factors considered included the quality of the evidence, gaps in current knowledge, and contextual issues related to the introduction of testing into clinical practice. Technical studies showed that the test was highly accurate in detecting common CYP450 gene variations, although less data was available for uncommon variations.
Further analysis focused on how well the test performed in predicting key clinical outcomes. The available data showed no consistent association between the results of CYP450 gene testing and the clinical response to SSRIs—that is, their effect on symptoms of depression. There was also no evidence that CYP450 testing predicted the risk of side effects, or that the results guided doctors' selection of SSRI drug or dosage.
In the absence of data that testing influences treatment or outcomes, there is a risk that the CYP450 test could increase costs without helping patients. There is also a possibility of harmful effects, such as less effective treatment or inappropriate use of genetic information.
The Working Group's findings don't mean that CYP450 testing is not potentially useful. Rather, there is currently "insufficient evidence" either for or against the use of CYP450 testing in patients beginning SSRI treatment for depression. The report includes some suggestions for future studies that might help to fill gaps in knowledge regarding the use of CYP450 testing for antidepressant treatment.
The recommendation is the first to be issued by the EGAPP initiative. "This first release from EGAPP has helped us understand some of the challenges we face in evaluating genomic innovations, such as the quality of research designs, dealing with data that are proprietary, scant evidence on benefits and harms, and the lack of comparisons with current practice, of testing in typical populations, and of information about cost and cost-effectiveness," said EGAPP Chair Alfred Berg, MD, MPH, of the University of Washington.
About the American College of Medical Genetics
Founded in 1991, the ACMG (http://www.acmg.net) provides education, resources and a voice for the medical genetics profession. To make genetic services available to and improve the health of the public, the ACMG promotes the development and implementation of methods to diagnose, treat and prevent genetic disease. Members include biochemical, clinical, cytogenetic, medical and molecular geneticists, genetic counselors, and other health care professionals committed to the practice of medical genetics. Genetics in Medicine, now published monthly, is the official journal of the ACMG.
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