For example, PAH concentrations in maternal serum have been reported to positively correlate with DNA methylation levels of several NTD-related genes, including CTNNA1, PAX3, and MYH2 (Wang et al., 2017; Lin et al., 2019); a pilot cross-sectional study conducted in Mexico found that urinary 1-hydroxypyrene, a PAH metabolite, was negatively associated with the methylation levels of interleukin 12 and p53 gene promoters (Alegria-Torres et al., 2013). This evidence concerns the gene CTNNA1 and pulmonary arterial hypertension.