PITX2 and atrial septal defect: Additionally, we noted an enrichment in genes from the semaphorin-plexin signaling pathway for ASD+VSD: knockdown of semaphorin3D reduces the size of the primary heart field [46], and semaphorin3C appears to be regulated by Tbx1, Pitx2, and Gata6—critical regulators of secondary heart field development [47]; PlexinA1-SemaD6 interaction are involved in myocardial organization and growth [48].