GBA1 and Parkinson disease: However, GCase appears to play a more general role in the pathogenesis of PD, as suggested by the decreased GCase activity detected in brain samples with increased α-syn levels and in CSF from sporadic PD patients without GBA1 mutations (Murphy and Halliday, 2014; Chiasserini et al., 2015; Rocha et al., 2015; Parnetti et al., 2017).