title: Increased risk of essential tremor in first-degree relatives of patients with Parkinson's disease.
abstract: We conducted a historical cohort study of 981 first-degree relatives of 162 patients with Parkinson's disease (PD) and of 838 first-degree relatives of 147 controls representative of the population of Olmsted County, Minnesota. In addition, we studied 2,684 first-degree relatives of 411 patients with PD referred to the Mayo Clinic. Relatives were interviewed and screened for tremor either directly or through a proxy, and those who screened positive were examined or copies of their medical records were obtained to confirm the diagnosis of essential tremor (ET). We also obtained ET information from a medical records-linkage system (family study method). In the population-based sample, the risk of ET was significantly increased for relatives of patients with onset of PD<or=66 years (first tertile; hazard ratio [HR]=2.24; 95% confidence interval [95% CI]=1.26-3.98; P=0.006). In the referral-based sample, the risk of ET among relatives increased with younger onset of PD in patients (linear trend; P=0.001), and was higher in relatives of PD patients with the tremor-predominant or mixed form when compared with relatives of patients with the akinetic-rigid form, and in men compared with women. These findings suggest that PD and ET may share familial susceptibility factors.
authors.affiliation: Division of Epidemiology, Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA. rocca@mayo.edu
authors.forename: Walter A
authors.initials: WA
authors.lastname: Rocca
authors.forename: James H
authors.initials: JH
authors.lastname: Bower
authors.forename: J Eric
authors.initials: JE
authors.lastname: Ahlskog
authors.forename: Alexis
authors.initials: A
authors.lastname: Elbaz
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Grossardt
authors.forename: Shannon K
authors.initials: SK
authors.lastname: McDonnell
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Schaid
authors.forename: Demetrius M
authors.initials: DM
authors.lastname: Maraganore
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D016001:Confidence Intervals; D020329:Essential Tremor / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics*; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications / Q000453:epidemiology / Q000235:genetics; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012306:Risk; D012737:Sex Factors