LRRK2 and Parkinson disease: The effect of mutations in PD-associated genes range from being “fully penetrant” (like SNCA triplications or missense variants causing monogenic PD forms), to conferring a “strong predisposition” to the disease (as SNCA duplications, or variants in LRRK2, VPS35, and CHCHD2), or to variants causing “medium predisposition”6.