**2.4. 22q11 deletion syndrome (DiGeorge syndrome, velocardiofacial syndrome, conotruncal anomaly face syndrome)**

Molecular studies demonstrate that the vast majority of patients with clinical diagnosis of DiGeorge, velocardiofacial, conotruncal anomaly face syndromes share a common genetic cause, namely a 22q11.2 deletion [43–45]. The prevalence is 1 in 4000 to 6000 live births, but the severity of the phenotype is variable and in some the features may go unrecognized [46]. CHD are estimated to occur in 75–80% of patients with a 22q11.2 deletion. The most common CHDs associated with 22q11.2 deletion include tetralogy of Fallot (TOF) and aortic arch anomalies. Other conotruncal lesions include pulmonary atresia with ventricular septal defect (VSD), and truncus arteriosus [47, 48]. In cases of truncus arteriosus, the truncal valve tends to be more dysplastic when the 22q11 deletion is present [49].

Identifying the cardiac patient with a 22q11.2 deletion early in life can provide substantial benefits to the child and family. Currently, it is recommended that infant with interrupted aortic arch type B, truncus arteriosus, TOF and isolated aortic arch anomalies undergo testing for a 22q11.2 deletion [22]. Prenatal diagnosis can be performed using FISH technology on samples obtained from chorionic villus sampling or amniocentesis if cardiac defects are present. Non-cardiac lesions are not easily diagnosed but, absent fetal thymus has been reported [50]. Many children initially present without cardiac symptoms in the form of recurrent infections. This may point to an underlying immunodeficiency associated with 22q11.2 deletion [51]. The risk of recurrence is in 50% as this is transmitted in an autosomal dominant inheritance if either parent carries the deletion. If neither parent carries the deletion, there may still be germline mosaicism, but the risk of recurrence is small (1%) [22, 48].
