Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. For a discussion of genetic heterogeneity of visceral heterotaxy, see HTX1 (306955).

Neurocardiofaciodigital syndrome (NCFD) is characterized by severe developmental delay, variable brain anomalies, congenital heart defects, dysmorphic facial features, and a distinctive type of synpolydactyly with a supernumerary hypoplastic digit between the fourth and fifth digits of the hands and/or feet. Other features include eye abnormalities, hearing impairment, and electroencephalogram anomalies (summary by Horn et al., 2021).

Cardiac valvular dysplasia-1 (CVDP1) is characterized by congenital malformations of the pulmonic, tricuspid, and mitral valves. Structural cardiac defects, including atrial and ventricular septal defects, single left ventricle, and hypoplastic right ventricle have also been observed in affected individuals (Ta-Shma et al., 2017). Genetic Heterogeneity of Cardiac Valvular Dysplasia CVDP2 (620067) is caused by mutation in the ADAMTS19 gene (607513) on chromosome 5q23.