GBA1 and Parkinson disease: Importantly, not only a rare mutation in the GBA1 gene increases the risk of developing PD/DLB, but also a decrease in GCase activity has been reported in the biofluid or brains of sporadic PD patients (Balducci et al., 2007; Gegg et al., 2012; Parnetti et al., 2014; Chiasserini et al., 2015; Rocha et al., 2015; Moors et al., 2019).