GBA1 and Parkinson disease: Some have demonstrated a higher odds ratio of developing PD, as well as an earlier age of PD onset, than in dual carriers vs those of only a LRRK2 G2019S or GBA variant.14,15 If these penetrance and age at onset findings are replicated, one explanation that may reconcile these with the finding of less severe nonmotor progression in carriers of dual LRRK2/GBA variations is that LRRK2 and GBA may differentially be associated with the development of PD (penetrance and onset) and the PD disease course (clinical course).