LRRK2 and Parkinson disease: While early candidate gene studies and subsequent meta-analyses provided conclusive evidence showing that polymorphisms in SNCA[6] (encoding alpha-synuclein), LRRK2[7] (leucine-rich repeat kinase 2), MAPT[8] (microtubule-associated protein tau), and GBA[9] (acid beta-glucosidase) significantly impact PD susceptibility, most association studies in the field provided inconclusive or even conflicting results.