GBA1 and Parkinson disease: Furthermore, α‐synuclein, in turn, may further reduce the availability of functional glucocerebrosidase,45, 49 and GCase activity is low even in PD patients without a GBA mutation, although to a lesser extent than those with a mutation.45 Thus, it is possible that therapeutics effective in GBA‐PD could also be of benefit for PD patients without a GBA mutation.