Background/Purpose: Microsomal epoxide hydrolase (EPHX) is an important enzyme that metabolizes harmful reactive epoxides from smoking. Genetic variations of this enzyme are thought to increase the risk of developing chronic obstructive pulmonary disease (COPD). The aim of this study was to confirm and advance our knowledge of the role of this genetic variation in COPD. In addition, the association between this gene and important COPD-related phenotype bronchodilator responses (BDRs) was studied. Methods: This was a hospital-based case-control study. The EPHX1 genetic mutations of 105 smokers with COPD and 103 control smokers without COPD were evaluated by polymerase chain reaction, followed by restriction fragment length polymorphism analysis. The association of genetic mutations and COPD phenotypes was also studied. Results: Subjects with EPHX1 113 (His 113/His 113) homozygote mutation had a strong correlation with COPD (odds ratio: 2.7, 95% confidence interval: 1.5-5.2). In addition, compared with other genotypes, the His 113 homozygote mutation patients had significantly lower BDRs, as shown by the absolute and percentage changes from baseline, in COPD patients (91.7 ± 12.5 mL vs. 141.6 ± 15.1 mL, p = 0.01 and 8.3 ± 1.2% vs. 13.4 ± 1.4%, p = 0.006). Conclusion: A strong correlation between the EPHX1 113 mutant homozygote and smoking-related COPD was noted. This genetic polymorphism was also associated with lower BDRs in COPD patients.
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