DNA methylation are closely related to environmental factors, such as stress, lifestyle, and occupational environment. The case group in our research came from compulsory detoxification centers, while the control group came from common living environments, which might affect the results. Secondly, this study could only match the factors of age and gender between the control group and the case group, however, there might be other factors influencing the results. In addition, the samples selected for this study were all male, and the methylation levels of CHN2 gene promoter may have differences between genders. Therefore, the interpretation of the results may not apply for women as well.
