The high prevalence and susceptibility of these mice to cleft lip is thought to be caused by a mutation in Wnt9b, which is also on the list of top clefting genes from human GWAS data (Juriloff et al., 2006; Yu et al., 2017) Wnt9b knockout mice exhibit cleft lip and, importantly, the expression of Fgf8, Fgf10, and Fgf17 is down-regulated in the tissue of facial processes forming the future lip in these mice. Here, FGF17 is linked to cleft lip.