NKX2-5 and Abnormal cardiac septum morphology: Various forms of progressive familial heart block (PFHB), progressive cardiac conduction defects (PCCD), and atrial septal defect with atrioventricular conduction defects have been described in families with dominant inheritance, implicating the genes SCN5A, NKX2.5, and TRPM4 [Benson et al., 1999; Kruse et al., 2009; Schott et al., 1999], but a recessive modes of inheritance has not been reported.