Modelling Tetralogy of Fallot: insights and limitations of animal models

Abstract

Tetralogy of Fallot (TOF) is the commonest cyanotic congenital heart disease, arising from antero-cephalad deviation of the outlet septum during outflow tract (OFT) morphogenesis, producing a ventricular septal defect, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. Despite advances in surgical correction, the developmental origins of TOF remain incompletely understood, and the genetic architecture of the majority of non-syndromic cases is yet to be resolved. Experimental models have been central to progress in this field, yet each model may capture only part of the disease. This review evaluates animal and genetic models of TOF across species, discussed in order of increasing cardiovascular similarity to humans. Zebrafish and Xenopus enable rapid in vivo interrogation of candidate genes and conserved developmental pathways, despite fundamental differences in cardiac anatomy. Avian models have been instrumental in defining the contributions of the second heart field and cardiac neural crest cells to OFT elongation and septation. Mouse models, with their four-chambered heart and amenability to precise genetic modification, have provided the most detailed mechanistic insights, and we examine key models across the multiple signalling pathways in depth. A recurring finding is that individual models reproduce discrete components of the TOF tetrad rather than its complete set of defects, frequently producing double outlet right ventricle or persistent truncus arteriosus rather than classical TOF. No single model fully recapitulates all four features with complete penetrance. Continued integration of human genomic data with targeted experimental perturbations will be essential for closing this gap.