LRRK2 and Parkinson disease: The majority of PD cases are of sporadic origin; however, about 10% are familial and the most common monogenic forms of PD are pathogenic variants on the LRRK2 gene that encode leucine-rich repeat kinase 2 (LRRK2) [46], a multidomain protein with a catalytic core that can fulfill kinase and GTPase activity.