A protein that initiates Alzheimer's disease has been identified by researchers at Harvard Medical School and Brigham and Women's Hospital in Boston.

The chemical, called presenilin, plays a major role in producing the waxy plaques that rob the brains of Alzheimer's victims of memory and cognition. Its identification provides a specific target for new drugs that might treat, or even prevent, the disease.

"Our evidence that presenilin is the long-sought key in the initiation of Alzheimer's now allows the scientific community to . . . try to design potent inhibitors to treat the disease," notes Dennis Selkoe, a professor of neurology. He and his colleagues report their work in the April 8 issue of the journal Nature.

Presenilin enhances production of a substance known as amyloid beta, which congeals into starchy clumps involved in inflammation and other changes in brain cells that cause their death. To date, no way has been found to control these marauding plaques.

"Since we know Alzheimer's develops when amyloid beta accumulates in the brain . . . ,I believe that in the future it may be possible to detect and treat it the same way we currently detect and treat high cholesterol, with routine screening tests and preventive drug therapy," Selkoe says. "To accomplish this, the next goal will be for academic and pharmaceutical scientists to find a drug that can inhibit amyloid-beta production and prevent the progression of the disease, the same way statin drugs currently lower cholesterol levels and slow hardening of the arteries for millions of people."

The Alzheimer's Association and other organizations say that 4 million people in the United States today have the disease. That figure is probably a minimum number because the malady cannot be positively identified until an autopsy is performed. Alzheimer's strikes about 10 percent of Americans older than 65 years, and almost half of those older than age 85. With the present rapid aging of the U.S. population, forecasts call for between 10 million and 14 million cases by the year 2050.