Sleep disorders may be caused by an imbalance of brain chemicals, two studies published today say.

The findings may help researchers better understand the causes of sleep problems, which affect millions of Americans, including those with brain diseases like Parkinson's.

The University of Michigan studies, reported in today's edition of Neurology, compared 13 people with multiple-system atrophy, a rare but fatal degenerative brain disease, with 27 healthy people. The 13 had both sleep disorders being studied: rapid eye movement (REM) sleep behavior disorder and obstructive sleep apnea. Researchers monitored the patients' movements, brain waves and breathing.

REM sleep behavior disorder was associated with a deficiency of dopamine and obstructive sleep apnea was linked to a deficiency of acetylcholine. Researchers used a brain scan to measure both chemicals that the brain uses to transmit information from one cell to the next.

A local sleep expert said the studies make a significant contribution to understanding the nature of the sleeping disorders and multiple system atrophy. "These are two very important complementary articles," said Dr. Thomas Roth, director of the sleep center at Henry Ford Hospital.

Lead researcher Sid Gilman described REM sleep behavior disorder as "instead of becoming paralyzed in the night when they dream, people thrash in their beds, sit up, speak. They often will pummel their bed partner."

People can get out of their beds and injure themselves without knowing.

Medication used to treat the disorder stimulates the production of dopamine. "We found a very strong correlation between the severity of the sleeping disorder and the level of decrease of dopamine," Gilman said.

The obstructive sleep apnea study yielded similar results with the brain chemical acetylcholine. People with sleep apnea snore, often quite loudly, Gilman said. They suddenly stop breathing because the tissues at the back of the mouth -- including the tongue -- become lax and fall over the airway opening. A person may experience total loss of breathing for a minute or longer until the pressure in the chest becomes so great that the person coughs or snorts, then resumes breathing normally.

Sleep apnea often occurs with people who are overweight or who have a short neck.

"It really seriously decreases the amount of oxygen in the blood," Gilman said. This can cause daytime drowsiness and affect reaction time while driving. Sleep apnea may also be associated with high blood pressure, stroke and heart attack.

Researchers found that patients with the lowest levels of acetylcholine had the most severe cases of sleep apnea.

More research is being conducted to further investigate these links. If a causal relationship is found, medicines can be developed to treat these disorders, Gilman said.

The next step is studying more patients with sleeping disorders, and patients with other neurological diseases, such as Parkinson's.

Many people with Parkinson's disease have REM sleep behavior disorder. Gilman said he suspects they also might have sleep apnea.

One-third of people with Parkinson's have memory loss. "It's possible that with the decrease of oxygen saturation in the blood, there can be increased damage in the brain, which can only make this situation worse." If a link to dopamine levels is found, medication alleviating Parkinson's can be advanced.

A Cornell sleep researcher touted these findings as "a major step forward in identifying the precipitating factors in many sleep disorders." Dr. James Maas, professor of psychology, noted that sleep apnea affects 18 million people and can be life-threatening.

"Isolating the biochemistry of that disorder can mean saving literally millions of lives," Maas said.

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Last updated: 07/10/2003 - 06:00 PM