While most PD cases are idiopathic, a familial form of the disease has been associated with mutations in > 20 genes, including parkin RBR E3 ubiquitin protein ligase (PRKN), PTEN-induced kinase 1 (PINK1), both of which encode component of the molecular apparatus that removes dysfunctional mitochondria (so-called mitophagy)94, leucine-rich repeat kinase 2 (LRRK2), encoding a multifunctional kinase, and synuclein alpha (SNCA)95. This evidence concerns the gene LRRK2 and Parkinson disease.