A few studies have focused on the activity of the lysosomal hydrolase ß-glucocerebrosidase (GCase) in alpha-synucleinopathies, with a significant decrease of GCase activity in the CSF of patients with PD compared to controls (Parnetti et al., 2014a; Lerche et al., 2021). Here, GBA1 is linked to Parkinson disease.