title: Familial aggregation of Parkinson disease: a comparative study of early-onset and late-onset disease.
abstract: BACKGROUND
  It is unclear whether late-onset Parkinson disease (PD), which is the most typical and most common form of the disease, has a familial component. Evidence for familial aggregation is key to whether research should focus on gene discovery or search for environmental factors.
  
  
  OBJECTIVE
  To investigate familial aggregation of early-onset and late-onset PD separately.
  
  
  METHODS
  Using survival methods, age-specific risk of PD was calculated and compared for 525 parents and siblings of 117 patients with early-onset PD, 1642 parents and siblings of 343 patients with late-onset PD, and 522 parents and siblings of 114 controls. The index patients were ascertained from a movement disorder clinic. Spouses and friends served as controls.
  
  
  RESULTS
  Compared with the relatives of controls, age-specific risk of PD was increased 7.76-fold in the relatives of patients with early-onset disease (P<.001) and 2.95-fold in the relatives of those with late-onset disease (P =.02).
  
  
  CONCLUSIONS
  Late-onset PD has a significant familial component. The magnitude of recurrence risk to relatives suggests a genetic etiology, without ruling out the possibility of a coexisting environmental component.
authors.affiliation: Department of Neurology, CR131, Oregon Health Sciences University, 3181 SW Sam Jackson Park Rd, Portland, OR 97201, USA. payamih@ohsu.edu
authors.forename: Haydeh
authors.initials: H
authors.lastname: Payami
authors.forename: Sepideh
authors.initials: S
authors.lastname: Zareparsi
authors.forename: Dora
authors.initials: D
authors.lastname: James
authors.forename: John
authors.initials: J
authors.lastname: Nutt
mesh_terms: D000328:Adult; D017677:Age Distribution; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009679:Nuclear Family; D010290:Parents; D010300:Parkinson Disease / Q000235:genetics* / Q000401:mortality*; D017678:Sex Distribution; D016019:Survival Analysis