These findings are strikingly to similar to the observations of Ratner and colleagues 2014 who also observed a younger age at onset of sporadic PD among subjects occupationally exposed to metals and pesticides.
Both studies used the same exposure history questionnaire and the Ward and Gibb diagnostic criteria for selection of subjects for research in PD. While the Ratner study looked at duration of exposure, the Gamache study looked at proximity and frequency. These two complimentary studies provide important insight into the role of chemical exposure duration and intensity in the age at onset of PD. Another related study using the same inclusion criteria by Wilk and colleagues (2006) found a younger age at onset of PD among subjects with familial PD exposed to herbicides who also had a single nucleotide polymorphism in a gene that codes for the enzyme glutathione-S-transferase (GST). Future studies designed to further elucidate the relationships between genetic factors that influence drug metabolism and exposure history are needed.
Dr. Ratner's commissioned work for the Workplace Safety Insurance Board (WSIB) of Ontario, Canada (a.k.a. "the Ratner Paper") set the standard used by the Workplace Safety Insurance Appeals Tribunal (WSIAT) for occupational chemical exposure claims related to age at onset of PD.
Link to Gamache article.
Link to Ratner article.
Link to Wilk article.
LInk to WSIAT