Parkinson's disease is characterized by a decline in the functions of the central nervous system, such as motor skills and speech. Several studies have shown an increased risk of dementia in first-degree relatives of Parkinson's disease patients, while other studies have not confirmed the association, according to background information in the article. "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," the authors write.
Walter A. Rocca, M.D., M.P.H, of the Mayo Clinic College of Medicine, Rochester, Minn., and colleagues studied 1,019 first-degree relatives of 162 patients with Parkinson's disease, 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 and 2,716 relatives of 411 patients with Parkinson's disease who were referred to the Mayo Clinic. Dementia and cognitive impairment were determined by responses to a telephone questionnaire or cognitive test and a review of participants' medical records.
"This study provides evidence that relatives of patients with Parkinson's disease have an increased risk of cognitive impairment or dementia. 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 write. Relatives of patients who experienced the onset of the disease at age 66 or younger had a particularly increased risk of developing dementia or cognitive impairment.
"The observed associations suggest the action of shared familial susceptibility factors, genetic or non-genetic," they conclude.