LRRK2 and Parkinson disease: Familial monogenic forms of PD have been identified, with the most common of these attributed to mutations in the leucine-rich repeat kinase 2 (LRRK2) [2], Parkin (PARK2) [3] and Glucosidase, Beta, Acid (GBA) [4] genes, and with several rare monogenic forms recognized, including rare mutations in the alpha-synuclein gene (SNCA) [1, 5].