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ObjectiveTo test the relationship between clinically relevant types of GBA mutations (none, risk variants, mild mutations, severe mutations) and β-glucocerebrosidase activity in patients with Parkinson disease (PD) in cross-sectional and longitudinal case-control studies.MethodsA total of 481 participants from the Harvard Biomarkers Study (HBS) and the NIH Parkinson's Disease Biomarkers Program (PDBP) were analyzed, including 47 patients with PD carrying GBA variants (GBA-PD), 247 without a GBA variant (idiopathic PD), and 187 healthy controls. Longitudinal analysis comprised 195 participants with 548 longitudinal measurements over a median follow-up period of 2.0 years (interquartile range, 1–2 years).Resultsβ-Glucocerebrosidase activity was low in blood of patients with GBA-PD compared to healthy controls and patients with idiopathic PD, respectively, in HBS (p < 0.001) and PDBP (p < 0.05) in multivariate analyses adjusting for age, sex, blood storage time, and batch. Enzyme activity in patients with idiopathic PD was unchanged. Innovative enzymatic quantitative trait locus (xQTL) analysis revealed a negative linear association between residual β-glucocerebrosidase activity and mutation type with p < 0.0001. For each increment in the severity of mutation type, a reduction of mean β-glucocerebrosidase activity by 0.85 μmol/L/h (95% confidence interval, −1.17, −0.54) was predicted. In a first longitudinal analysis, increasing mutation severity types were prospectively associated with steeper declines in β-glucocerebrosidase activity during a median 2 years of follow-up (p = 0.02).ConclusionsResidual activity of the β-glucocerebrosidase enzyme measured in blood inversely correlates with clinical severity types of GBA mutations in PD. β-Glucocerebrosidase activity is a quantitative endophenotype that can be monitored noninvasively and targeted therapeutically.

This Danish study1 “confirmed (β2-adrenoreceptor [β2AR]) agonist use to be associated with reduced Parkinson disease (PD) risk…,” replicating larger studies in Israel2 and Norway.3 However, the authors' speculations regarding causality, and that smoking may confound the association, conflict with their own study. First, they did not collect smoking data. In Israel,2 the association remained significant after directly adjusting for smoking (which was collected) and smoking-related covariates. Second, even after adjusting for COPD diagnosis, inhaled corticosteroids, and inhaled anticholinergics (their “markers of smoking”), β2AR agonists were significantly associated with reduced PD risk with an OR of 0.64 (0.42–0.98) compared with 0.66 (0.52–0.85) without adjusting (table 4).1 Adjusting for the smoking markers did not attenuate the OR. Once these covariates are statistically controlled, any remaining significant relation between β2AR agonists and reduced PD risk cannot be due to their mediating effects. Whether covariates themselves are related to PD risk is not directly relevant. Third, the beta-blocker propranolol, which increased neuronal SNCA,3 was associated with increased PD risk in Denmark (excluding essential tremor),1 Norway (restricted to cardiovascular indications),3 and Israel (5–8 years lag).2 Finally, β2AR agonists, associated with reduced PD risk after adjusting for smoking-related covariates in Norway,3 Israel,2 and Denmark,1 offered neuroprotection in 3 rodent models.3–5 Thankfully, rodents don't smoke.

OBJECTIVE: To test the relationship between clinically relevant types of GBA mutations (none, risk variants, mild mutations, severe mutations) and β-glucocerebrosidase activity in patients with Parkinson disease (PD) in cross-sectional and longitudinal case-control studies. METHODS: A total of 481 participants from the Harvard Biomarkers Study (HBS) and the NIH Parkinson's Disease Biomarkers Program (PDBP) were analyzed, including 47 patients with PD carrying GBA variants (GBA-PD), 247 without a GBA variant (idiopathic PD), and 187 healthy controls. Longitudinal analysis comprised 195 participants with 548 longitudinal measurements over a median follow-up period of 2.0 years (interquartile range, 1–2 years). RESULTS: β-Glucocerebrosidase activity was low in blood of patients with GBA-PD compared to healthy controls and patients with idiopathic PD, respectively, in HBS (p < 0.001) and PDBP (p < 0.05) in multivariate analyses adjusting for age, sex, blood storage time, and batch. Enzyme activity in patients with idiopathic PD was unchanged. Innovative enzymatic quantitative trait locus (xQTL) analysis revealed a negative linear association between residual β-glucocerebrosidase activity and mutation type with p < 0.0001. For each increment in the severity of mutation type, a reduction of mean β-glucocerebrosidase activity by 0.85 μmol/L/h (95% confidence interval, −1.17, −0.54) was predicted. In a first longitudinal analysis, increasing mutation severity types were prospectively associated with steeper declines in β-glucocerebrosidase activity during a median 2 years of follow-up (p = 0.02). CONCLUSIONS: Residual activity of the β-glucocerebrosidase enzyme measured in blood inversely correlates with clinical severity types of GBA mutations in PD. β-Glucocerebrosidase activity is a quantitative endophenotype that can be monitored noninvasively and targeted therapeutically.

Objective: To better understand cross-sectional relationships between CSF and PET measures of tau pathology, we compared regional and global measures of 18 F-T807 (AV-1451) PET to CSF protein levels of total tau (t-tau), phosphorylated tau (p-tau), and β-amyloid 1–42 (Aβ42). Methods: T-tau, p-tau, and Aβ42 levels were assessed using INNOTEST xMAP immunoassays. Linear regression was used to compare regional and global measures of 18 F-T807 standardized uptake value ratios (SUVR) to CSF protein levels using data from 31 cognitively unimpaired elderly participants in the Harvard Aging Brain study. Results: After controlling for sex and age, total cortical 18 F-T807 binding was significantly correlated with p-tau (partial r = 0.48; p r = 0.30; p = 0.12). Regional 18 F-T807 measures were more strongly correlated with CSF protein levels than the global measure, with both t-tau and p-tau significantly correlated with 18 F-T807 SUVR in entorhinal, parahippocampal, and inferior temporal cortical regions (partial r = 0.53–0.73). Peak correlations between CSF and PET measures of tau were similar to those between CSF and PET measures of amyloid burden. Finally, we observed significantly higher temporal T807 SUVR in individuals with high amyloid burden. Conclusions: These data support the link between 18 F-T807 PET and CSF measures of tau pathology. In these cognitively normal individuals with 18 F-T807 binding largely restricted to the temporal lobe, 18 F-T807 SUVR in temporal regions appeared more reflective of CSF t-tau and p-tau than a total cortical measure.