al., 2001; Hata et al., 2002). Active demethylation of DNA can occur through hydroxymethylation, with the formation of 5-hydroxymethylcytosine (5-hmC) catalyzed by the ten-eleven translocation methylcytosine dioxygenase (TET) family of enzymes (Guibert and Weber, 2013). It should be noted that the majority of studies discussed in this review do not distinguish between 5mC and 5hmC. Methylation patterns are highly dynamic across development and methylation is a critical part of stage-dependent gene regulation (Guibert and Weber, 2013; Monk et al., 2016; Monk et al., 1987). Thus, disruption of methylation patterns during gestation or postnatally by teratogens would have lasting ramifications on ongoing developmental processes. In addition, environmentally-driven alterations to methylation status can remain stable across the lifespan and even be perpetuated across generations (Laird, 2003; Meaney and Szyf, 2005).
