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In recent years, Pope John Paul II had been visibly weakened by Parkinson's disease. This ScienCentral News video reports on some of the new advances in treatments for the disease.
Pope John Paul II was one of the most vigorous, well-traveled popes in history. But in his last years, Parkinson's disease made him frail and weak. People with Parkinson's often experience muscle rigidity, trembling, difficulty walking, and problems with balance and coordination. There is no cure for this progressive neurological disorder.
Parkinson's disease is caused by a loss of the brain cells called neurons that produce a chemical called dopamine. Without enough of this important neurotransmitter, parts of the brain become overactive and sufferers lose control of their muscle activity. "We really don't understand what dopamine does in the normal situation," says Mark West, a psychology professor at Rutgers University. "We know what happens when dopamine's been lost — movement becomes very difficult. In some way then, dopamine helps the brain's motor system function smoothly.
"The typical drug given is L-Dopa, which the brain converts into dopamine, and thus, some of the dopamine that's been lost is replaced," says West. The drug, developed more than 30 years ago, remains the most effective treatment. But doctors admit L-Dopa is only a bandaid for the symptoms and for some patients, it works only temporarily.
"It was pretty clear over time," explains Michael Kaplitt, a professor of neurological surgery at New York Presbyterian-Weill-Cornell Medical Center. "Parkinson's disease patients will suffer with this disorder for a long period of time — for 15, 20, 30 years or more. And after they've taken these drugs for a long period of time, a lot of things can happen. For some patients, they can become increasingly resistant to the medication after years of taking it, so they will require increasing doses of the medication, or they'll require more numerous doses throughout the day. But even with that they continue to worsen." Kaplitt also says some patients develop side effects from the medication, like dyskinesia, which is an involuntary writhing movement.
Deep brain stimulation. image: Medtronic
A surgical treatment called deep brain stimulation can treat the symptoms in some patients. The tip of a very thin wire is put inside the brain in an area that controls movement. The wire then runs through a small hole in the skull and under the scalp, to a device called a neurostimulator, which is implanted under the collarbone. The neurostimulator sends tiny electrical impulses down the wire into the brain that can quiet the over-activity. But there are limitations to this treatment.
"You have to leave this hardware in the body," says Kaplitt. "There's a risk of infection whenever you put something foreign in the body. There's the possibility it could break over time. You have to change the batteries every few years, which requires another operation. So, for a lot of these reasons, it's not ideal."
In August, 2003,55-year-old Nathan Klein became the first patient to undergo gene therapy for Parkinson's. Surgeons at the New York Presbyterian-Weill-Cornell Medical Center injected billions of viruses into his brain, each carrying a gene for a chemical substance that will re-set the overactive brain cells.
"We can introduce a gene into an area of the brain that will change the function of cells in the brain," says Kaplitt, who published research on the efficacy of gene therapy for Parkinson's in the October 11, 2002 issue of Science. "So the gene itself becomes like a drug, except it's a fairly permanent drug. By putting the gene in, the cells can start making what they need and become their own little permanent factories to make what they need."
Researchers hope gene therapy will offer better treatment for Parkinson's disease and bring them closer to a cure. Nearly one and a half million Americans currently live with Parkinson's, and approximately 50,000 more receive a diagnosis of the disease every year.