GBA p.T369M substitution in Parkinson disease: Polymorphism or association? A meta-analysis

Abstract

The lysosomal enzyme glucocerebrosidase (GCase), encoded by GBA, has an important role in Parkinson disease (PD). GBA mutation carriers have an increased risk for PD, earlier age at onset, faster progression, and various nonmotor symptoms including cognitive decline, REM sleep behavior disorder, hyposmia, and autonomic dysfunction.(1) Furthermore, GCase enzymatic activity is reduced in the peripheral blood(2) and brain(3) of noncarrier, sporadic PD patients. Biallelic GBA mutations, which have been classified as "severe" or "mild," may cause Gaucher disease (GD), a lysosomal storage disorder. Mild mutations may lead to GD type 1, and 2 severe mutations result in neuronopathic GD (type 2 and type 3).(4) There are 2 GBA variants, p.E326K and p.T369M, which do not cause GD in homozygous carriers, but may modify GCase activity and GD phenotype. It is now clear that p.E326K is a risk factor for PD,(5) but whether p.T369M is associated with PD is still controversial. In some studies, the p.T369M substitution was associated with PD,(6) while in others it had similar or increased frequency in controls. Of interest, it was recently demonstrated that the GBA p.T369M substitution was associated with reduced enzymatic activity in patients with PD and controls compared with that in noncarriers (7.64 vs 11.93 μmol/L/h, p < 0.001).(2) Of interest, it was even lower than the average enzymatic activity of the p.E326K substitution, which was 9.81 μmol/L/h. Because clinical trials on GBA-associated PD are ongoing, and because treatment specifically targeting GBA is likely to be available in the future, it is important to determine whether the GBA p.T369M substitution is associated with PD.

Figure 1.. Meta-analysis of the GBA p.T369M substitution in Parkinson disease

(A) Forest plot of meta-analysis of 14 case-control cohorts including 4,920 patients with Parkinson disease and 3,500 controls with data on the GBA p.T369M substitution (references and details on the cohorts are in the supplemental data). The Cochran-Mantel-Haenszel test was performed, and the pooled odds ratio (OR) was 1.78 (95% confidence interval [CI] = 1.25–2.53, Cochran-Mantel-Haenszel = 9.63, df = 1, p = 0.002). Heterogeneity is statistically significant (Tarone test, χ² = 26.84, df = 12, p = 0.01). (B) Forest plot of meta-analysis of 12 case-control cohorts including a total of 4,320 patients and 2,925 controls with data on the GBA p.T369M substitution, after excluding the 2 outliers cohorts that introduced the heterogeneity (see supplemental data for details). The Cochran-Mantel-Haenszel test OR was 1.74 (95% CI = 1.19–2.55, Cochran-Mantel-Haenszel = 7.58, df = 1, p = 0.0059), and the heterogeneity was not statistically significant (Tarone test, χ² = 13.88, df = 11, p = 0.28).