LRRK2 and Parkinson disease: Leucine-rich repeat kinase 2 (LRRK2), the most commonly mutated gene in both familial and sporadic Parkinson’s disease (PD), is a large (2527 amino acids, 286 kDa) multidomain protein and is widely expressed in many tissues and cells, especially in the brain (Islam and Moore, 2017; Kang and Marto, 2017).