RISK OF PARKINSONS-DISEASE AMONG FIRST-DEGREE RELATIVES - A COMMUNITY-BASED STUDY

Objective: To determine the relative risk (RR) and cumulative incidenc e of idiopathic Parkinson's disease (PD) in first-degree relatives of PD patients compared with relatives of controls from the same geograph ic region. Design: A family history questionnaire was used to obtain i nformation on all first-degree relatives of cases and controls. A subs et of these first-degree relatives was also examined. A Cox proportion al hazards model with double-censoring techniques for missing informat ion was used to model the RR for PD, adjusting for gender, ethnicity, and relationship to proband. Results. A total of 1,458 first-degree re latives of 233 PD patients were 2.3 times as likely (95% CI = 1.3 to 4 .0) as 7,834 relatives of 1,172 controls to develop PD. The cumulative incidence of PD to age 75 among first-degree relatives of PD patients was 2% compared with 1% among first-degree relatives of controls. The risk in male first-degree relatives was higher than in female relativ es (RR = 2.0, 95% CI = 1.1 to 3.4) and the risk in relatives of Caucas ians was higher than in African-Americans and Hispanics (RR = 2.4, 95% CI = 1.4 to 4.1). Risk for siblings and parents of probands was simil ar. Conclusions: Susceptibility to PD is increased in first-degree rel atives of both sporadic and familial cases. The pattern of inheritance and the relationship between genetic and environmental risk factors w arrant further study.