The MR26F8 mice had both striking craniofacial defects (Fig. 2A-F, Fig. S3A,B, Fig. S4) as well as limb defects including sirenomelia and post-axial polydactyly (Fig. S3C-L), the latter phenotypes consistent with the expression of the Msx2-Cre transgene in the limb bud ectoderm (Sun et al., 2000). The gene discussed is MSX2; the disease is sirenomelia.