A combination of genetic predisposition and environmental factors is the most intriguing topic to understand the basis of PD early-onset; the chronic interaction with toxic substances in the living environment certainly increases the possibility to develop damages to the mitochondria, which are responsible for the increase of Reactive Oxygen Species (ROS) in the body, and which are closely associated with the production of misfolded α-Synuclein 14. The gene discussed is SNCA; the disease is Parkinson disease.