TWIST1 and Saethre-Chotzen syndrome: Such CV malformations were also observed in a more profound mouse model of Saethre-Chotzen syndrome, in which one Twist1 allele possesses a loss-of-function mutation and the other Twist1 allele is deleted in the periosteal dura and sutures (known as Twist1fl/–;Sm22a-Cre mice) (9).