The small group of drug addicts in the United States who unwittingly injected a bad batch of synthetic narcotic around 1982 had no idea that some of their number would develop a Parkinson's disease-like illness within weeks.1 It transpired that the chemist who had made the offending drug had unwittingly synthesised 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which proved to be a potent and specific nigral toxin. A postmortem examination of one such affected patient showed prominent cell loss in the substantia nigra with a single eosinophilic inclusion similar to a Lewy body.

Not surprisingly, this discovery gave an enormous boost to the environmental theories of Parkinson's disease …