Long Term Smoking Significantly Reduces the Risk of Parkinson's Disease
A greater than 40% decrease in Parkinson's if you smoke more than 30 years? So it seems from this huge NIEHS study of 305,468 Americans. "Smoking Duration, Intensity, and Risk of Parkinson Disease".
Obviously the risk of getting lung cancer, emphysema, etc from smoking is much higher. Still, if you knew you had the genes that protects you from lung disease (whatever they are) but not the ones that protect you from Parkinson's (whatever they are) would you smoke?