TBX1 and coronary artery disorder: At 8% oxygen, there was no significant difference in the incidence and severity of CHDs in Tbx1+/− or Nkx2.5+/− fetuses compared with Tbx1+/+ or Nkx2.5+/+ fetuses, respectively [140], whereas at 5.5% oxygen, a significantly higher CHD risk was observed in Tbx1+/− compared with Tbx1+/+ of the same litter exposed to low oxygen levels.