From the Gbx2+/−;Pax9+/− intercross only three Gbx2−/−;Pax9−/− mice were recovered from a total of 172 offspring, one each at P0, E15.5 and E10.5, and these mice displayed the typical Pax9−/− phenotypes, as well as AVSD and full CAT (with an isolated right subclavian artery), both of which are defects not previously seen in either Gbx2−/− or Pax9−/− embryos (Figure 6; Table 1 and Table 2). This evidence concerns the gene PAX9 and familial atrioventricular septal defect.