Over the past two decades, genes have clearly been linked to monogenic PD, including three autosomal dominantly inherited ones (alpha-synuclein (SNCA), leucine-rich repeat kinase 2 (LRRK2), and vacuolar protein sorting-associated protein 35 (VPS35)) and three recessively transmitted ones (E3 ubiquitin ligase Parkin (Parkin), PTEN-induced putative kinase 1 (PINK1), and protein deglycase DJ-1 (DJ-1)). This evidence concerns the gene SNCA and Parkinson disease.