SNCA and Parkinson disease: Familial monogenic forms defined by rare and pathogenic variants in autosomal dominant (e.g., SNCA, LRRK2, VPS35) or recessive (PRKN, PINK1, PARK7) PD-related genes, account for less than 10% of Mendelian cases (Lesage and Brice, 2009; Karimi-Moghadam et al., 2018).