MONDAY, Oct. 8, 2007 (HealthDay News) -- Relatives of people with Parkinson's disease face up to a 73 percent increased risk for developing Alzheimer's disease, suggests a new study that says genetics could be to blame.
Parkinson's disease causes declines in functions of the central nervous system, such as impaired motor skills and speech.
"The co-occurrence of Alzheimer's disease and Parkinson's disease in families and in individuals may be due to the sharing of susceptibility genetic variants," according to the report in the October issue of the Archives of Neurology.
In the study, Dr. Walter A. Rocca, of the Mayo Clinic College of Medicine in Rochester, Minn., and colleagues collected data on 1,019 first-degree relatives of 162 patients with Parkinson's disease, and on 858 relatives of 147 people who were the same age and sex as someone in the Parkinson's disease group but did not have the condition. Also included were 2,716 relatives of 411 patients with Parkinson's disease who were referred to the Mayo Clinic.
The researchers found that relatives of those with Parkinson's had a 37 percent increased risk of developing Alzheimer's, compared to those with relatives who didn't have the disease. Moreover, relatives of people who developed Parkinson's before the age of 66 were 73 percent more likely to develop Alzheimer's, the study found.
"We studied brothers, sisters, parents and children of patients with Parkinson's diseases and looked at how many developed dementia or cognitive impairment," said study co-author Dr. James H. Bower, also of the Mayo Clinic. "We found that if you had a first-degree relative with Parkinson's disease, you are more likely to develop cognitive impairment or dementia than if you didn't have a first-degree relative with Parkinson's disease.
"These are different diseases," Bower said, "but there looks to be some shared risk factors for both diseases. We don't know what these shared risk factors are. One could be genetic, but it could be environmental. We have to start looking at neurodegenerative diseases as having a common mechanism. If we could find the cause of one, it could lead to cures and understanding of others."
One expert sees a potential connection between a mechanism at work in both diseases.
"This study provides strong evidence for some increase in risk for cognitive decline and dementia in relatives of Parkinson's disease victims," said Greg M. Cole, a neuroscientist at the Greater Los Angeles VA Healthcare System and the associate director of the Alzheimer's Disease Research Center at UCLA's David Geffen School of Medicine. "The authors conclude with the logical inference that Parkinson and Alzheimer diseases share some genetic or environmental risk factors."
Likely common risk factors for both diseases could be oxidative damage and inflammation, Cole said.
More information
To learn more about Parkinson's disease, visit the U.S. National Institute of Neurological Disorders and Stroke.
