1,3 butadiene 1 1,3-butadiene 1 5 methyltetrahydrofolic acid 1 5,10 methylenetetrahydrofolate reductase (FADH2) 1 Article 1 China 1 Chromosomal damage 1 DNA methylation 1 DNA methylation age 1 Folate metabolism 1 MTHFR 1 Polymorphism 1 adult 1 butadiene diepoxide cell culture 1 cell nucleus 1 chromosome damage 1 clinical article 1 controlled study 1 female 1 folate metabolism 1 gene frequency 1 genetic damage 1 genomic DNA 1 genotoxicity 1 genotype 1 human 1 human cell 1 in vitro study 1 lymphoblastoid cell 1