Comparative analysis of methods for measuring glucocerebrosidase enzyme activity in patients with Parkinson's disease with the GBA1 variant.

GBA1 variants are significant genetic risk factors for Parkinson's disease (PD). Accurately measuring glucocerebrosidase (GCase) activity is crucial for understanding disease progression and developing targeted therapies. This study aimed to validate strategies for measuring blood GCase activity in patients with GBA1-associated PD (GBA-PD). We recruited 25 GBA-PD patients and 27 matched PD patients without GBA1 variants (non-GBA-PD). GCase activity from fresh blood was quantified using the 4-methylumbelliferyl β-D-glucopyranoside leukocyte assay (GCaseRaw). The GCase patient/normal control ratio (GCase ratio) was calculated for consistency. GCase activity in dried blood spot (DBS) specimens (GCaseDBS) and plasma glucosylsphingosine (GluSph) levels were measured using LC-MS/MS. The diagnostic accuracy was assessed using area under the curve (AUC) values. No significant differences in demographics or disease characteristics were found between GBA-PD and non-GBA-PD patients. GCase activity was significantly lower in patients with GBA-PD (p < 0.001). The GCase ratio exhibited a higher diagnostic accuracy (AUC, 0.93) than GCaseRaw (AUC, 0.88) or GCaseDBS (AUC, 0.78). Plasma GluSph levels were higher in GBA-PD patients and were negatively correlated with the GCase ratio (r = -0.326; p < 0.01). The relative ratio of GCase activity showed a strong discriminatory potential, distinguishing between GBA-PD and non-GBA-PD.