When it comes to genetic tests for mental illness, there is still no solid evidence that these tests do anything but give consumers a false sense of control. Dr. Doug Levinson, the director of the Program on the Genetics of Brain Function... at Stanford University, which studies the genetic basis of psychiatric disorders, said in an interview that there is a scientific consensus based on the study of twins that manic depression is 80 percent-85 percent genetic and schizophrenia is 70 percent-80 percent genetic. But most scientists in the field, he also explained, have concluded that we don’t simply carry one gene for depression. Instead, depression and other mental illnesses are the result of many genes interacting in a delicate balance with life experience.
It would be difficult for one test to capture this kind of information, and Levinson has counseled patients to skip genetic testing. Another expert, Harvard's Michael Miller, MD, told writer Rachel Lehmann-Haupt that test results, even if accurate, might yield little practical information for patients:
“People want information for all sorts of reasons-out of desperation, hope,” said Miller. “It’s overly simplistic to think that by learning that the switch in your genetic code is in this position and not in that position is ultimately going to have a lot of practical impact. If a person feels depressed, they’re still going to have to go through the trial and error process of psychotherapy to determine whether they need a drug, a change of job, or to spend more time at the gym.”