Parkinson's Puzzle: Study Shows Genetic Link
Dec. 13, 2000 -- For some time, researchers have realized that patients who get the first symptoms of Parkinson's disease before age 50 may have inherited a predisposition to the disease. The more typical form of Parkinson's, where symptoms appear after the age of 50, may also have a genetic basis, according to new research published in the Dec. 14 issue of TheNew England Journal of Medicine.
The disease is thought to result from a lack of the brain chemical dopamine. Symptoms may include stiff, slow movement, and tremor or shaking involving mostly the hands.
Researchers of the new study reached their conclusions by examining Iceland's health care database and found that patients who did develop Parkinson's later in life were much more likely to also have relatives with the disease.
"Iceland is a great place to study ... common diseases," says Bogi Andersen, MD. Anderson, who was not involved in the study, is assistant professor of medicine at the University of California, San Diego.
The computerized Icelandic Healthcare Database is a unique resource, containing information on the more than 600,000 individuals who have lived in Iceland over the past 11 centuries and includes all 270,000 individuals still living. Thanks to limited immigration, Iceland's population represents a relatively pure genetic pool with roots tracing back to the Vikings.
The researchers, from the National University Hospital in Reykjavic, reviewed database records for more than 750 patients with Parkinson's disease, including more than 550 who developed the disease after age 50. The risk of having Parkinson's disease was more than six times higher for siblings, three times higher for children, and more than two times higher for nieces or nephews of individuals with the disease.
Previous studies have found toxic chemicals and other environmental factors that may be responsible for causing Parkinson's disease in older individuals. Although this study looked for genetic factors, it did uncover some evidence that environmental factors also play a role. The researchers say that because they did not find an increased risk of the disease in spouses, environmental factors later in life were unlikely to play a significant role.
On the other hand, they note that siblings of Parkinson's patients were much more likely to have the disease than the patients' children. This could suggest that an environmental factor early in life might contribute to the development of Parkinson's later on. The researchers conclude that this -- combined with the fact that the pattern of affected relatives was similar in both early- and late-onset forms of Parkinson's disease -- means that both genetic and environmental factors are important.
The researchers add that more research is needed in both areas. Andersen agrees and adds that unraveling the genetic puzzle of the disease "is a difficult undertaking and unlikely to be just around the corner."