"I'm scared," said Jackie Lustig, 52, of Sudbury, Mass., whose father died of Alzheimer's and whose mother is living it. "I'm hoping to heck that the pharmaceutical companies come up with something better than there is now. It's not a nice way to go."

The study, appearing in March's Archives of Neurology, found more than 22 percent of the adult children of 111 couples with Alzheimer's had the disease themselves. Risk grew with age. Among offspring older than 60, more than 30 percent were affected. In those older than 70, nearly 42 percent had the disease.

Prior studies have found a 6 to 13 percent prevalence of the disease in the U.S. population older than 65.

At age 62, Gayle Dorman worries every time she misplaces her car keys. "Is this the day I'm going to start losing it?" she wonders.

The suburban Tacoma, Wash., woman spent eight years caring for her parents, who died of Alzheimer's, and in a cruel coincidence, her husband's mother, who also died of the illness.

She said she was surprised to learn "a lot of other people have a double whammy like I do." No one knows how many people have two afflicted parents, but experts say that as baby boomers age, there are likely to be more.

For now, there's no cure for the more than 26 million people worldwide estimated to have Alzheimer's, which gradually destroys memory and other mental abilities.

Dorman took part in the University of Washington study to find out more about her risk and to help researchers identify culprit genes that could lead to new treatments. Families were recruited through the university's Alzheimer's research center.

In the study, diagnoses were confirmed through medical records, autopsies and examination by researchers. The parents with Alzheimer's had 297 children who lived to adulthood and 67 of those children had Alzheimer's.

Senior author Dr. Thomas Bird of the University of Washington said he was uncomfortable saying the normal risk tripled or quadrupled in people with two affected parents because the study was small and had no comparison group.

"What I'm comfortable saying is that risk is increased and we're working on trying to find out what the magnitude is," Bird said.