SMAD6 and coronary artery disorder: The CHD disease genes, which have been identified to date, suggest that all aspects of developmental signaling pathways may be involved in human CHD: from ligands (e.g. JAG1) and receptors (e.g. NOTCH, PDGFRA), across down-stream signaling effectors (e.g. PTPN11, SMAD6), to transcription factors (e.g. GATA4, NKX2-5) and targets (e.g. ACTC1, MYH6) (Fig. 1).