The U.S. Food and Drug Administration has given the thumbs up to St. Jude Medical (NYSE: STJ) that allows the Minnesota medical device maker to expand a clinical study of a deep brain stimulation device to treat major depressive disorder.

St. Jude announced Monday that the Broaden severe depression study that is testing its Libra investigational device will now be conducted at 20 medical centers with a total of 125 patients. Before the FDA approval, the study was being conducted at three centers in Chicago, New York and Dallas.

Similar studies are being conducted outside the U.S., said Rohan Hoare, St. Jude's vice president, research and development. The company believes the market opportunity for deep brain stimulation to treat depression is more than $1 billion.

Deep brain stimulation works by sending mild pulses of current from an implanted device to stimulate the brain. DBS leads are surgically placed within a target area in the brain and connected to a neurostimulator that is usually implanted under the skin near the collarbone.

"We are committed to leading this important research in hopes of finding a solution for people who currently don't have a treatment option," said Chris Chavez, president of the St. Jude Medical Neuromodulation Division, in a statement. "By expanding the Broaden study, we are able to continue to add to the body of evidence that will determine if deep brain stimulation is indeed an option for managing major depressive disorder."

Patients who fit a specific profile can only be enrolled in the Broaden study. The criteria are that the patient has to have been clinically diagnosed with major depressive disorder (MDD), be between 21 and 70 years old, has experienced his first depressive episode before age 45 and has tried at least four treatments in his current episode such as different medications, different combinations of medications, and/or electroconvulsive therapy.

The National Institute of Mental Health (NIMH) estimates that there are 21 million adults in the U.S. who suffer from some kind of depressive disorder, and of these, about 4 million live with severe depression that cannot be controlled by medications, psychotherapy and in certain cases, ECT.

Deep brain stimulation can help to manage the condition and provide symptom relief, but it is not a cure, according to the Mayo Clinic's website,

St. Jude's Libra DBS treatment for depression is not approved in the U.S. But St. Jude has launched the Libra platform to manage Parkinson's disease in DBS in Europe and Australia. That is a $500 million market, according to company officials.

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