Though we have mainly focused on the relative severity of Efnb1+/Δ mutant phenotypes, it is important to stress that Efnb1Δ/Y and Ephb1; Ephb2; Ephb3 compound mutant mouse embryos exhibit significant craniofacial dysmorphogenesis that includes hypertelorism, frontonasal dysplasia, and cleft secondary palate [8,41,58–60]. This evidence concerns the gene EFNB1 and frontonasal dysplasia.