title: Clustering of Parkinson disease: shared cause or coincidence?
abstract: BACKGROUND
  The spatial and temporal pattern of excessive disease occurrence, termed clustering, may provide clues about the underlying etiology.
  
  
  OBJECTIVE
  To report the occurrence of 3 clusters of Parkinson disease (PD) in Canada.
  
  
  METHODS
  We determined the population groups containing the clusters, geographical limits, and duration of exposure to the specific environments. We tested whether there was an excessive presence of Parkinson disease by calculating the probability of the observed cases occurring under the null hypothesis that the disease developed independently and at random in cluster subjects. Results of genetic testing for mutations in the alpha-synuclein, parkin, tau genes, and spinocerebellar ataxia genes (SCA2 and SCA3) were negative.
  
  
  RESULTS
  The probabilities of random occurrence (P values) in the 3 clusters were P = 7.9 x 10 (-7)for cluster 1, P = 2.6 x 10 (-7)for cluster 2, and P = 1.5 x 10 (-7)for cluster 3.
  
  
  CONCLUSIONS
  Our findings indicate an important role for environmental causation in Parkinson disease. A possible role exists for environmental factors such as viral infection and toxins in the light of current evidence.
authors.affiliation: Pacific Parkinson's Research Centre, Vancouver Hospital and Health Sciences Centre, University of British Columbia, 2221 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5.
authors.forename: Ajit
authors.initials: A
authors.lastname: Kumar
authors.forename: Susan M
authors.initials: SM
authors.lastname: Calne
authors.forename: Michael
authors.initials: M
authors.lastname: Schulzer
authors.forename: Edwin
authors.initials: E
authors.lastname: Mak
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Wszolek
authors.forename: Chris
authors.initials: C
authors.lastname: Van Netten
authors.forename: Joseph K C
authors.initials: JK
authors.lastname: Tsui
authors.forename: A Jon
authors.initials: AJ
authors.lastname: Stoessl
authors.forename: Donald B
authors.initials: DB
authors.lastname: Calne
mesh_terms: D000328:Adult; D000368:Aged; D016000:Cluster Analysis; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010300:Parkinson Disease / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics