The risk of PD is inversely correlated with smoking, according to research from INSERM, U708 Neuroepidemiology, and University Pierre et Marie Curie, Paris, France, Groupe hospitalier Pitié Salpêtrière, Paris Cedex, France. Overall, the research found that the NOS1 gene contributes to PD susceptibility. The gene discussed is NOS1; the disease is Parkinson disease.