In an α-synuclein PFF-based transmission assay, where human α-synuclein PFFs trigger the aggregation of endogenous α-synuclein, α-synuclein aggregation was enhanced by LRRK2 G2019S compared to WT, but was decreased by the loss of LRRK2 in PD patient-derived neurons differentiated from induced pluripotent stem cells [136]. This evidence concerns the gene LRRK2 and Parkinson disease.