Clustering of Parkinson disease: shared cause or coincidence?
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.
Kumar
Ajit
A
Pacific Parkinson's Research Centre, Vancouver Hospital and Health Sciences Centre, University of British Columbia, 2221 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5.
Calne
Susan M
SM
Schulzer
Michael
M
Mak
Edwin
E
Wszolek
Zbigniew
Z
Van Netten
Chris
C
Tsui
Joseph K C
JK
Stoessl
A Jon
AJ
Calne
Donald B
DB
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