Major depression is more likely to be a heterogeneous group of disorders rather than a single condition, Dr. Sidney Kennedy, professor of psychiatry at the University of Toronto, told Benefits Canada’s Mental Health Summit in Toronto.
In fact, research has identified more than 200 different combinations of symptoms that qualify for the diagnosis of a major depressive episode. “For example, you could have a sad mood and four of the physical symptoms . . . or you could have loss of interest and pleasure with four additional symptoms relating to negative thinking and pain. So why would you think treatment would be the same when you have such different pathways to depression?” said Kennedy.
Since it’s virtually impossible to predict which cluster of symptoms will respond best to which type of therapy, biomarkers may provide answers, he said. “Biomarkers can be biological characteristics to predict response to a specific treatment or they may signal an imminent relapse.”
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Potential biomarkers include genes, proteins, neurotransmitters, hormones, brain activity and pharmacogenetic tests. When it comes to measuring treatment outcomes, pharmacogenetic tests can identify variations in the enzymes that metabolize psychiatric medications. Patients who are slow metabolizers for a specific enzyme may experience greater side-effects and require a lower dose or a different medication. Quick metabolizers, on the other hand, may require higher doses to achieve good results. Since about 90 per cent of people are normal metabolizers, the majority of patients don’t require pharmacogenetic testing at the outset of treatment.
Although Kennedy said there are no good studies yet to show better outcomes in terms of improving the response to a medication or characterizing side-effect risk, he thinks the tests are coming. “I think pharmacogenetic testing is a promising and interesting field, but it’s not yet ready for prime time.”