H19 and type 2 diabetes mellitus: Metformin-exposed mouse fetuses were shown to elevate H19 expression (Deng et al., 2017), a lncRNA reported to be related to T2DM and influence DNA methylation (Ding et al., 2012), which induces hypomethylation and the overexpression of HNF-4α, thus efficiently repressing hepatic gluconeogenesis (Figure 2).