TUESDAY, Feb. 7, 2006 (HealthDay News) -- Genes may play a much bigger role in Alzheimer's disease than previously thought, a new study involving twins suggests.
In fact, Alzheimer's disease may have a genetic cause in up to 80 percent of cases, according to the report published in the February issue of the Archives of General Psychiatry.
"Our finding confirms the higher estimates that have been suggested previously," said lead researcher Margaret Gatz, a professor of psychology at the University of Southern California, in Los Angeles.
The study, which involves data on nearly 12,000 elderly participants in the Swedish Twin Registry, is 10 times larger than any previously done, Gatz said.
"This doesn't mean that environment is not important," Gatz stressed. "Environment may be relevant not only for whether, but also for when one gets the disease. Also, you can't go from these results to any one individual."
It's a study "that had to be done in Sweden, where everyone is in the health-care system," added William Thies, vice president for medical and scientific affairs of the Alzheimer's Association. "What they're measuring is whether both twins get Alzheimer's disease or not -- and they find a pretty high correlation."
The study doesn't have all the information Thies would like to see, however.
"What we don't see much of in here are data on the different ages of onset, on whether people get it at 65 or 85," he said. "If you had the choice, you would much more like to have it later."
Right now, doctors have nothing to offer patients in terms of slowing the disease's progression, Thies noted. However, in the future, when hoped-for treatments for Alzheimer's emerge, people with a family history of the illness may routinely go in for brain scans to detect early disease onset. Early detection would mean early intervention and a better chance of slowing or stopping the illness, Thies said.
"The equation is open to future adjustment as we get medications that affect the progression of the disease," Thies said. "Brain scans will offer information about who gets treated and who doesn't."
Two other studies in the same issue of the journal addressed another continuing debate: Whether depression increases the risk of developing Alzheimer's disease. And they seemed to arrive at conflicting results.
One study, led by Dr. Michael A. Rapp, a researcher at the Alzheimer's Research Center of Mount Sinai School of Medicine in New York City, included 95 Alzheimer's patients in nursing homes. It found that those with a history of depression had a higher number of Alzheimer-associated plaques and tangles in their brains.
"We found that depression might affect cognitive decline over time, but further studies are needed," Rapp said.
The other study followed nearly 1,300 adults over the age of 67 for 12 to 15 years. Every two years, the researchers looked for evidence of depression as well as any decline in mental function.
Having depression at the start of the study did not predict the onset of Alzheimer's disease, the researchers found.
"What we concluded is that if a clinician sees a patient who is both depressed and cognitively impaired, the impairment may be related to the depression, [but] if the person's impairment continues to progress over time, it is not due to the depression," said lead researcher Dr. Mary Ganguli, a professor of psychiatry and epidemiology at the University of Pittsburgh.
The study did show that depression is associated with poor mental function, "but we've known that for some time," Thies said. "People with poor memories tend to be depressed."
More information
For more on Alzheimer's, visit the Alzheimer's Association.
