GBA1 and Parkinson disease: The ‘pathogenic’ mutations associated with GD result in significant reduction in glucocerebrosidase enzyme activity, which underlies its clinical manifestations.5 33 However, polymorphisms such as E326K result in a relatively minimal reduction in enzyme activity,22 and the fact that these predispose to PD without being associated with GD, supports the concept that the pathogenic mechanisms of GBA1-PD are distinct from those of GD.