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In previous study, we have found the catechol-O-methyltransferase (COMT) Val158Met polymorphism may be associated with the risk of Parkinson's disease (PD) in Asians, especially Japanese population. In this study, we further evaluated the associations of PD wearing-off susceptibility with COMT polymorphisms. We carried out a retrieval of studies and included the relevant studies which met the criteria. After the data were extracted, the Stata software 11.0 was used to analyse the genotype frequencies. A total of five studies were included. The pooled result indicated that genotype AA was significantly associated with the wearing-off risk of PD (AA vs. others: OR = 2.52, 95 % CI 1.21-5.26, P = 0.013; AA vs. GA: OR = 2.51, 95 % CI 1.18-5.34, P = 0.017; AA vs. GG: OR = 2.17, 95 % CI 1.09-4.33, P = 0.027). The results also showed allele A was correlated with PD wearing-off risk (A vs. G: OR = 1.95, 95 % CI 1.18-3.22, P = 0.009). In conclusion, this study suggested that Val158Met polymorphisms in COMT may increase the risk of wearing-off. Further studies with larger sample sizes are needed to confirm our results.

In previous study, we have found the catechol-O-methyltransferase (COMT) Val158Met polymorphism as an associated risk factor for Parkinson's disease (PD) in Asian rather than Caucasian populations. The aim of this study was to further evaluate the associations of PD risk with COMT polymorphisms in different Asian populations. We carried out a retrieval of studies that investigated associations between COMT Val158Met polymorphism and PD risk in Asians, and included the study if it met the eligibility criteria. Stata version 12.0 was used to analyze the data. A total of 13 studies including 1,834 patients and 2,298 controls were included. The overall result indicated that COMT Val158Met polymorphism was significantly associated with the risk of PD in Asians (AA vs others: OR = 1.58, 95 % CI 1.26-1.97, p < 0.001; GG vs AA: OR = 0.63, 95 % CI 0.47-0.85, p = 0.002; AA vs GA: OR = 1.58, 95 % CI 1.24-2.00, p < 0.001). In Japanese population, the homozygote AA tends to increase the risk of PD (AA vs others: OR = 1.54, 95 % CI 1.10-2.15, p = 0.012; AA vs GA: OR = 1.61, 95 % CI 1.14-2.29, p = 0.008). This study showed that the Val158Met polymorphism of COMT gene may be associated with PD in Japanese rather than Chinese population. Further studies are needed to confirm this association in more ethnicities.