SNCA and Parkinson disease: In addition to PD-causative mutations, classical candidate gene association approaches or more recently large genome-wide association studies (GWAS) have identified common genetic variants in genes such as SNCA, LRRK2, microtubule-associated protein tau gene (MAPT) or glucosylceramidase beta (GBA) which contribute to increase PD susceptibility (Lill, 2016).