Issue date: 3/25/08 Section: News
A worse night's sleep, due to nerve damage
For sleep apnea patients, nerve-cell loss causes weak muscles, makes treatment difficult
Julia Harte

Penn researchers have discovered that sleep apnea - a disorder characterized by periodic lapses in breathing while asleep, usually due to an obstructed airway - results in probably irreversible muscle weakness, which can make the condition even worse.

The findings are a "major breakthrough," according to Jerry Siegel, a professor at UCLA's Center for Sleep Research.

The Penn research explains why previous treatments were not entirely successful - the nerve damage that researchers see "is probably irreversible and makes breathing harder and impairs alertness," Siegel said.

Sleep apnea causes its patients to lose motor neurons, which are the cells that transmit impulses from a person's central nervous system to muscles throughout the body.

Losing these cells can weaken muscles and aggravate the usual symptoms of sleep apnea, such as trouble breathing or a decrease in overall alertness.

"You no longer have enough neurons to keep the muscles excited," said Sigrid Veasey, associate professor at Penn's School of Medicine and the leader of the research team.

Most researchers in the past tried to physically expand the blocked airway of their patients with surgery or masks that pumped pressurized air through patients' noses, oblivious to the damage that sleep apnea was wreaking on nerve cells.

Until now, nobody knew why expanding the airway did not completely restore sleep apnea patients to full health.

The damage that motor neurons sustain from sleep apnea depends on their original state of health.

Motor neurons that are healthy when challenged with low or fluctuating oxygen levels can clean up abnormal proteins that otherwise clog the cell. Unhealthy cells, however, may simply self-destruct.

Surprisingly, what makes a cell healthy or unhealthy has a lot to do with diet, according to Veasey.

"A diet of high fried foods or meat at high temperatures really sets up the motor neurons for a problem," she said. "An obese person stuck with sleep apnea is going to have a lot more muscle weakness than a healthier person."

Loss of motor neurons is also behind other degenerative diseases such as Alzheimer's, Lou Gehrig's disease and Parkinson's.

While sleep apnea does not cause any of these diseases, it may accelerate their destructive course in patients.

Veasey's team is now researching ways to treat sleep apnea in light of its findings. Although they have not yet come up with a specific drug, Veasey noted that the best treatments will likely combine several techniques for protecting cells against varying oxygen levels - ranging from a healthier diet to actual gene therapy.

"At least we now have a target, so we know which directions to look in," she said.

According to Siegel, almost no researchers had examined the cellular processes of nerve damage in sleep apnea patients before. Their research "has the potential to help millions of people," he said.

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