The risk of developing PD in smokers was greater compared to non-smokers and men with genotype G. In women, the odds ratio was 0.62 for smokers compared to non-smokers with genotype GG/GA, and 0.64 for those with genotype A. These results suggested the existence of gender differences with regard to the modifying effect of the MAO-B genotype on the association of smoking with PD [22]. The gene discussed is MAOB; the disease is Parkinson disease.