January 2, 2008
Relatives of patients with Parkinson's disease may have an increased risk of developing dementia or memory problems, researchers report. And the younger the age at which Parkinson's appears, the greater the likelihood that family member will develop dementia. The findings appeared in the October issue of the Archives of Neurology, one of the journals from the American Medical Association.
Doctors have long sought clues that may link Alzheimer's disease, the most common form of dementia, and Parkinson's, a distinct neurologic ailment. Parkinson's disease is characterized by a decline in the functions of the central nervous system, including the ability to walk, move and speak. Several clinical and population studies have shown an increased risk of dementia in first-degree relatives of people with Parkinson's disease. However, other studies have not confirmed a link between the two.
In the current study, researchers at the Mayo Clinic in Rochester, Minnesota, looked at various subsets of patients with and without Parkinson's, as well as their close relatives. The study included 1,019 first-degree relatives of 162 patients with Parkinson's disease who were living near the Mayo Clinic. As controls, they included 858 relatives of 147 people in the same geographic area who were approximately the same age and sex makeup as people in the Parkinson's disease group but did not have the condition. In addition, the researchers evaluated 2,716 relatives of 411 patients with Parkinson's disease who were referred to the Mayo Clinic from a wider geographic area.
The study group surveyed the participants with a telephone questionnaire as well as cognitive tests and a review of medical histories to assess the occurrence of memory problems. These would include conditions like mild cognitive impairment, as well as more serious conditions like Alzheimer's and other forms of dementia. They found that relatives of patients with Parkinson's disease were at increased risk of cognitive impairment or dementia.
Relatives of patients who experienced the onset of the disease at age 66 or younger were at particularly high risk of developing dementia or cognitive impairment. "This association is primarily driven by families of patients with younger age at onset of Parkinson's disease, but the risk does not vary across relatives of patients with different clinical characteristics of Parkinson's disease," the authors wrote.
Although this study did not determine whether cognitively impaired or demented participants had Alzheimer's or some other condition, it is likely that at least some of the study participants had Alzheimer's. Both Alzheimer's and Parkinson's affect the brain, though the two disorders are distinct. However, as this study shows, there may be genetic links between Parkinson's and other neurological diseases. It is possible that Parkinson's and certain forms of dementia share common genes that predispose family members to one or both conditions. There may also be undiscovered environmental factors that lie at the root of these diseases.
Nobody is sure what causes Alzheimer's, although advancing age, genetic factors, and a host of additional risk factors may play a role. Just because someone in your family has Parkinson's disease doesn't mean you'll get the disease or get Alzheimer's or another form of dementia. Still, it is important that researchers continue to delve into the root causes of brain disorders like Alzheimer's and Parkinson's. Only through basic research will medical scientists be able to uncover the underlying mechanisms of disease and develop new and effective treatments.
The Fisher Center for Alzheimer's Research Foundation continues to fund critical research into the root causes of Alzheimer's disease. To learn more, visit www.ALZinfo.org, The Alzheimer's Information Site.
Walter A. Rocca; James H. Bower; J. Eric Ahlskog; Alexis Elbaz; Brandon R. Grossardt; Shannon K. McDonnell; Daniel J. Schaid; Demetrius M. Maraganore; "Risk of Cognitive Impairment or Dementia in Relatives of Patients With Parkinson Disease," Archives of Neurology, October 2007; Volume 64(10): pages 1458-1464.