NEW YORK (Reuters Health) - Relatives of patients with Parkinson's disease appear to be at increased risk for impaired thinking and dementia, suggesting the presence of shared susceptibility factors, new research indicates. Whether these factors are genetic or whether they relate to a shared lifestyle will require further study.

The association is primarily seen among families of patients who are younger when the develop Parkinson's disease, "but the risk does not vary across relatives of patients with different (symptoms) of Parkinson's disease," Dr. Walter A. Rocca, from the Mayo Clinic College of Medicine in Rochester, Minnesota, and colleagues report in the Archives of Neurology.

Rocca's team conducted a study involving 1019 first-degree relatives of 162 Parkinson's disease patients and 858 relatives of 147 similar subjects without the disease. Thinking ability was measured via telephone questionnaire or, in demented subjects, by interviewing close associates. In addition, the medical records of demented subjects were reviewed to confirm the diagnosis.

Relatives of Parkinson's disease patients were 37 percent more likely to show thinking deficits or dementia than were relatives of unaffected subjects, the report indicates.

As noted, the heightened risk in relatives was most apparent if Parkinson's disease developed at 66 years of age or younger. Relatives of patients with Parkinson's at a younger age were 73 percent more likely to have thinking impairments or dementia than were relative of unaffected subjects.

To confirm their findings, the researchers also examined the risk of thinking impairments in 2,716 first-degree relatives of 411 Parkinson's disease patients referred to the Mayo Clinic. This analysis showed that the association was confined to relatives of patients with younger age at onset.

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