title: Familial Aggregation and Co-Aggregation of Essential Tremor and Parkinson's Disease.
abstract: BACKGROUND
  Current data suggest that the 2 common tremor disorders, essential tremor (ET) and Parkinson's disease (PD), may be associated with one another. Familial aggregation studies allow one to further explore their relatedness.
  
  
  METHODS
  Probands with ET (n = 110), PD (n = 130) or both ET and PD (n = 27) and control probands (n = 177) reported whether they had relatives with these diseases or with non-specific tremor.
  
  
  RESULTS
  A greater proportion of ET probands than control probands reported relatives with ET (30.0 vs. 2.8%, p < 0.001), non-specific tremor (38.2 vs. 13.6%, p < 0.001) and both ET and PD in different relatives (6.4 vs. 0.6%, p = 0.004). A greater proportion of PD probands than control probands reported relatives with PD (20.0 vs. 8.5%, p = 0.003), ET (11.5 vs. 2.8%, p = 0.002) and both ET and PD in different relatives (6.9 vs. 0.6%, p = 0.002).
  
  
  CONCLUSIONS
  This study provides evidence for the aggregation of ET in ET families and PD in PD families, and the familial co-aggregation of ET and PD.
authors.affiliation: Department of Neurology, Yale School of Medicine, Yale University, New Haven, Conn., USA.
authors.forename: Elan D
authors.initials: ED
authors.lastname: Louis
authors.forename: Lorraine
authors.initials: L
authors.lastname: Clark
authors.forename: Ruth
authors.initials: R
authors.lastname: Ottman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D020329:Essential Tremor / Q000453:epidemiology* / Q000235:genetics; D005190:Family; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000453:epidemiology* / Q000235:genetics