Hi Soccertese,
I don't neccesarily agree with the paper, I call it "a suggestion" which I find interesting, and posted it for information. Are you correct when you say there are no clusters of PD in the UK/USA? Have you any data or links? Is there any data on zinc clusters?
I accept that this is not a peer reviewed article, but it sounds feasible to me, and I will search around it to see can I find any confirmation. A brief look turned up the ref.

http://content.karger.com/ProdukteDB...oduktNr=224263

"Conclusions: Parkinson disease is substantially more common in Whites, and is nonrandomly distributed in the Midwest and Northeastern US",

Thanks for your input, it is only by bouncing these suggestions off each other that we will make progress.
best wishes
Ron