Although most cases are idiopathic, approximately 10% of PD cases are familial, and more than 20 causative genes with high penetrance have been identified including synuclein alpha (SNCA), parkin RBR E3 ubiquitin protein ligase (PRKN), and leucine rich repeat kinase 2 (LRRK2).3–6. This evidence concerns the gene LRRK2 and Parkinson disease.