Cono-truncal defects represent an anatomically heterogeneous group of CHDs affecting the outflow tract of the ventricles and the arterial pole of the heart. The most common malformations of this group are tetralogy of Fallot, pulmonary atresia with ventricular septal defect, truncus arteriosus and interrupted aortic arch. These CHDs are associated with genetic syndromes in 25-40% of cases and even in non-syndromic forms show a high incidence of mono-genic abnormalities.
Atrio-ventricular canal is a complex malformation due to abnormal septation of the “crux cordis” resulting in ostium primum atrial septal defect, inlet ventricular septal defect and common atrio-ventricular valve. It is almost always associated with genetic syndromes, being non-syndromic in only 25% of cases. However, septal defects other than atrio-ventricular canal are rarely due to genetic syndromes, ranging from 3% to 25% of cases, yet with a high rate of segregation in some families.
Valvular or vascular-elicited right sided obstructions, are due to genetic syndromes in about 10% of cases and this association results in difficult treatment due to the ineffectiveness of any percutaneous treatment and extent of the lesions along the pulmonary trunk.
Among left heart obstructions, supra-valvular stenosis is a well-know malformation due to disruption of the elastin gene associated with Williams syndrome in many cases.
Conversely, aortic coarctation and other left-sided heart stenosis or hypoplastic malformation are often non-syndromic, being associated with genetic syndromes in less than 10% of cases.
In conclusion, improved molecular genetic technologies has led to the discovery of several causes of syndromic and non-syndromic CHDs. Nevertheless, much work remains in identifying in etiology of non-syndromic CHDs, since the number of genes known to be involved is still limited.
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