A complex etiology is exemplified in the digenic inheritance (SAP130, PCDHA9) of left heart hypoplasia with a ventricular septal defect in the Ohia mouse57 and reinforced by the occurrence of right heart rather than left heart disease (tricuspid valve dysplasia/atresia) and extra-cardiac abnormalities in pigs edited to be SAP130 deficient58. The gene discussed is SAP130; the disease is heart disorder.