Risk of Cognitive Impairment or Dementia in Relatives of Patients with Parkinson Disease

Background: The evidence for increased risk of dementia in relatives of patients with Parkinson disease (PD) remains conflicting.

Objective: To study the risk of cognitive impairment or dementia in first-degree relatives of patients with PD.

Design, Setting, And Participants: We conducted a historical cohort study of 1019 first-degree relatives of 162 patients with PD and of 858 relatives of 147 matched controls representative of the population of Olmsted County, Minnesota. In addition, we studied 2716 first-degree relatives of 411 patients with PD referred to Mayo Clinic.

Main Outcome Measures: We administered via telephone a cognitive test directly to relatives or a dementia questionnaire to proxies. For relatives reported by proxies to have dementia, we obtained copies of their medical records to confirm the diagnosis. We also obtained dementia information from a medical records-linkage system.

Results: In the overall population-based sample, the risk of cognitive impairment or dementia was increased in relatives of patients with PD compared with relatives of controls (hazard ratio, 1.37; 95% confidence interval, 1.03-1.81; P = .03) and was particularly increased in relatives of patients with onset of PD at age 66 years or younger (youngest tertile; hazard ratio, 1.73; 95% confidence interval, 1.21-2.46; P = .003). The findings were consistent in several sensitivity analyses. In the referral-based sample, the risk of cognitive impairment or dementia in relatives increased with younger age at onset of PD but did not vary by other clinical characteristics.

Conclusion: Cognitive impairment or dementia may share familial susceptibility factors with PD (genetic or nongenetic).