LRRK2 and Parkinson disease: Although the majority of PD cases are caused by environmental factors or unknown factors (termed idiopathic or sporadic cases), approximately 10% of PD cases are caused by mutations in over 12 different genes involved in the regulation of proteasomal degradation pathways (Parkin, UCHL-1), mitochondrial homeostasis (PINK1, Omi/Htra, DJ-1, LRRK2), antioxidant response pathways (DJ1), lysosome function (ATP13A2), and mitophagy (PINK1 and Parkin) [25,26].