TNNT2 and Myocardial fibrosis: The B1KO died before E11.5 (see Supplementary material online, Table S2), a more severe phenotype than the published transgenic Cre line Nkx2.5Cre mediated Itgb1 knockouts,23 in which Itgb1fl/fl was deleted at a later developmental stage, the Mlc-2vCre mediated knockout, which results in myocardial fibrosis and cardiac failure in the adult heart,20 and the cTnT-Cre or Xmlc2Cre/+ mediated knockouts, which display defects in myocardial integrity and died around E14.5.21,22 The B1KO hearts display an abnormal OFT morphogenesis with a significantly large angle of Dog-Leg bend (Figure 1G–I).