Environmental pollutants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a prototypic AHR ligand, have been shown to interfere with embryonic development in an Ahr-dependent manner, causing teratogenic effects such as cleft palate and hydronephrosis (Mimura et al., 1997). This evidence concerns the gene AHR and cleft palate.