A handful of genes may be responsible for causing major depressive disorder, according to a first-of-its-kind study by psychiatrists at the University of Miami Leonard M. Miller School of Medicine. The findings, published in the Proceedings of the National Academy of Sciences, promise to help lift the stigma associated with clinical depression and open the door to finding targeted ways to treat it.
"This is a totally new area of research, this is a very novel finding," said Ma-Li Wong, M.D., professor and vice chair for translational research in the Department of Psychiatry and Behavioral Sciences. "This gene and this family of genes have not been looked at as a source for depression."
Dr. Wong and Julio Licinio, M.D., professor and chairman of the Department of Psychiatry and Behavioral Sciences at UM, and their colleagues, studied 284 patients diagnosed with depression. The researchers then genotyped the patients and examined a family of enzymes called cyclic nucleotide phosphodiesterases (PDEs), which are already therapeutic targets for a variety of illnesses. PDE inhibitors are medications known to be useful for treating several conditions such as heart disease, asthma, inflammation, and erectile dysfunction.
When the researchers compared PDE genes between the patient population and 331 people without depression, they identified several genes with key differences. There was an especially strong correlation between PDE9A and PDE11A and patients with depression. "Primarily, the strongest findings are on one gene, PDE11A, which is important for both susceptibility and also drug response," said Wong. "The PDE9A is also important, although not as significant, and there are other genes that offered preliminary data that needs to be confirmed. So there is a whole family of genes there that potentially are important for susceptibility and also treatment response."
The clinical work for this study was done at the David Geffen School of Medicine at UCLA, with the genotyping handled by the Sanger Institute in England. Licinio and Wong left UCLA to join the faculty of the UM Miller School of Medicine May 1. They are considered national leaders in the treatment of depression, and Licinio says the UM Miller School is now the only center currently involved in the study of these genes in depression.
This finding is particularly exciting for the researchers and for patients because it opens a whole new arena of study - and possibly a new way to treat depression. "The patients much prefer this idea of a genetic link, because for them the worst thing is to think it's their fault that they are depressed," said Licinio.
This work also holds the promise of much better diagnosis and treatment of major depressive disorder in the future. "We're trying to identify who is more likely to have depression and to respond to antidepressants, and the other thing is that this family of genes could become a new therapeutic target," he said.
Targeting these new genes could both improve and accelerate how patients respond to antidepressants. "Right now it's a guessing game, so there is no test or no marker that tells you which person is more likely to respond to a specific drug," said Licinio. And because of that, a physician may keep a patient on a single medication for a month or more waiting to see if they'll respond before trying another medication. But if psychiatrists can identify antidepressants that can effectively inhibit the effect of PDE11A or PDE9A, patients with those genes can expect both a better and faster response to medications.
Wong M, Whelan F, Deloukas P, Whittaker P, Delgado M, Cantor RM, McCann SM, Julio Licinio J.
Phosphodiesterase genes are associated with susceptibility to major depression and antidepressant treatment response
PNAS 2006, Sep 28; 0.1073/pnas.0602795103
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