Rick,
Your post came though while I was posting mine so I did not see it until after mine posted.
Very interesting also on the zinc comments, seems to be a connection.

I can't help feeling that the clusters idea is a red herring, since I feel sure the distribution of zinc and also PD is bound to have some clusters, whatever the mechanism of PD. If clusters are identified of both PD and zinc, the crucial question is do they occur together?

http://www.ncbi.nlm.nih.gov/pubmed/10100031
Evidence of functional zinc deficiency in Parkinson's disease.

http://www.jacn.org/cgi/content/full/20/2/106
Zinc deficiency has been suggested to occur in Parkinson's disease and may be specifically related to the vision, olfactory and taste loss in these patients

http://lpi.oregonstate.edu/ss03/zinc.html
The Antioxidant Function of Dietary Zinc and Protection Against Neural Disorders


There seems to be a lot of literature on the role of zinc in PD.

Ron