Glucocerebrosidase Activity is not Associated with Parkinson's Disease Risk or Severity

BACKGROUND: Mutations in the GBA gene, which encodes the lysosomal enzyme glucocerebrosidase (GCase), are risk factors for Parkinson's disease (PD). OBJECTIVE: To explore the association between GCase activity, PD phenotype, and probability for prodromal PD among carriers of mutations in the GBA and LRRK2 genes. METHODS: Participants were genotyped for the G2019S-LRRK2 and nine GBA mutations common in Ashkenazi Jews. Performance-based measures enabling the calculation of the Movement Disorder Society (MDS) prodromal probability score were collected. RESULTS: One hundred and seventy PD patients (102 GBA-PD, 38 LRRK2-PD, and 30 idiopathic PD) and 221 non-manifesting carriers (NMC) (129 GBA-NMC, 45 LRRK2-NMC, 15 GBA-LRRK2-NMC, and 32 healthy controls) participated in this study. GCase activity was lower among GBA-PD (3.15 ± 0.85 μmol/L/h), GBA-NMC (3.23 ± 0.91 μmol/L/h), and GBA-LRRK2-NMC (3.20 ± 0.93 μmol/L/h) compared to the other groups of participants, with no correlation to clinical phenotype. CONCLUSIONS: Low GCase activity does not explain the clinical phenotype or risk for prodromal PD in this cohort.