GBA1 and Parkinson disease: GBA1-PD patients tend to present symptoms at earlier age and develop more severe non-motor symptoms (olfactory dysfunction, dysautonomia, cognitive decline, and psychiatric symptoms), particularly those carrying complex or severe pathogenic variants as compared to those carrying mild pathogenic or risk variants (the latter increasing PD risk but not being pathogenic for GD), supporting a genotype–phenotype association [8, 9].