The penetrance of LRRK2 variations (specifically G2019S), or the chance that a carrier of this variation will manifest PD by late adulthood, has been estimated at 26% to 43% and is lower in individuals with GBA variations, ranging from 9% to 19%.5,6,7,8 Therefore, additional risk factors are clearly at play.9,10,11 One potential critical interaction is the association of GBA and LRRK2 variations in carriers of both variations (hereafter, LRRKR2/GBA). This evidence concerns the gene LRRK2 and Parkinson disease.