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Calming the tremors of Parkinson's disease remains a challenge for patients and doctors alike, but new research suggests that future therapies for the condition may emerge from an unlikely place: people's sleep habits.

Scientists at Sacre-Coeur Hospital at the University of Montreal report in the journal Neurology that Parkinson's can be predicted relatively accurately up to 12 years before the first muscle tremors appear. People diagnosed with an unusual sleep condition called REM sleep disorder, in which they physically act out their dreams by kicking, screaming and even harming themselves and others lying next to them, are 18% more likely to develop a neurodegenerative disease like dementia or Parkinson's within five years of their diagnosis, and 52% more likely after 12 years. "We have been aware of the potential connection between REM sleep disorder and these diseases for some time, but this is the largest and longest study to estimate the true risk of getting Parkinson's and other neurodegenerative diseases if someone has the sleep disorder," says Dr. Ron Postuma, the study's author and a neurologist at Montreal General Hospital. (See the top 10 medical breakthroughs of 2008.)

The trial involved nearly 100 men and women with an average age of 65, all diagnosed with REM sleep disorder. During normal sleep, our muscles become paralyzed when we enter the REM, or dream state, which explains why inside our dreams, we occasionally feel as if we can't move or are operating in slow motion. People with REM sleep disorder, however, never achieve this muscle relaxation, and researchers now believe that this could be the first sign of Parkinson's. The latest thinking on the disease holds that the uncontrolled movements that are the hallmark of Parkinson's are only the latest and most advanced sign of the disease, the final stage of a 10- or 20-year gradual decline in nerve function. In fact, experts believe that the condition actually begins with a loss of smell and a degeneration of nerves in the olfactory tract, then proceeds to the gut and brain stem. At some point along this march, the nerve damage hits the pons, a region in the brain that regulates sleep. "So in Parkinson's, there is a period that we don't know how long it lasts, in which the neurons are dying in the brain, just not in the motor areas," says Postuma. "And sleep is an area where this degeneration occurs, indicating that the process of Parkinson's has started."

Postuma stresses that REM sleep disorder is a rare condition not to be confused with the tossing and turning that most of us do every night. People with the condition have vivid movements nearly every night, and unlike those who sleepwalk or sleeptalk and remain confused for a bit after they awake, these patients are completely alert and oriented once they wake up.

REM sleep disorder itself can be treated with medications, but those drugs won't slow the decline in nerve function that's responsible for Parkinson's. But identifying the disease at this earlier stage may help scientists come up with newer ways of protecting the motor neurons from further damage. "We don't have agents now to stop the degeneration of Parkinson's," says Postuma. "But once we have those agents, as far as I'm concerned, every patient with REM sleep disorder should be taking it."

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• Scientists say a rare sleep disorder may be a precursor to the eventual onset of severe symptoms of the disease