CTSB and Parkinson disease: Lastly, given the genetic interaction between variants in CTSB and GBA1 in PD risk [10] and that catB has been found to regulate glucocerebrosidase (GCase) activity in HEK293 cells [60], we assessed the impact of catB inhibition on lysosomal GCase activity in DA neurons using the fluorogenic probe PFB-FDGlu (Fig. 3I-K).