A Japanese drug that protects laboratory rats from the kind of nerve damage seen in people with Huntington's disease is now being tested in humans with the disorder, according to researchers at the Johns Hopkins School of Medicine.

For the past two years, doctors in Japan and parts of Europe have used the drug -- idebenone -- to treat strokes. When injected into animals who exhibit symptoms similar to those of Huntington's, it prevented brain cell degeneration.

Huntington's disease is an incurable and untreatable neurological disorder that is hereditary; its sufferers gradually lose cells in two areas of the brain: the basal ganglia and the cerebral cortex. The lost cells affect patients' intellect, eventually resulting in dementia and psychosis. Victims also suffer from uncontrollable spasms.

An estimated 25,000 Americans have the disease, which strikes those over 30. And 100,000 more whose parents had it are at risk.

Scientists suspect that Huntington's disease is caused by overstimulated brain receptors.

Joseph Coyle, a professor of neuroscience at Hopkins who is investigating idebenone said, "Right now, we haven't pinpointed the agent that causes the excessive activation."

Although Huntington's is unique to humans, Coyle developed an animal model for the disease in 1975. He found that kainic acid, a derivative of seaweed, affects a certain type of brain cell, causing symptoms similar to Huntington's in rats.

Coyle discovered that idebenone counteracted the damage caused by kainic acid and was effective in limiting nerve cell degeneration in rat brains.