Risk of 22q11.2 deletion in fetuses with right aortic arch and without intracardiac anomalies

Objective: To assess the risk of 22q11.2 deletion in fetuses with a prenatal diagnosis of right aortic arch without intracardiac anomalies (RAA-no ICA). Methods: This was a retrospective study of all fetuses with RAA-no ICA diagnosed prenatally at three referral centers, between 2004 and 2014. A detailed sonographic examination was performed in each case, including visualization of the thymus and of the head and neck vessels to identify the presence of an aberrant left subclavian artery (ALSA). Karyotyping and fluorescence in situ hybridization analysis for diagnosis of 22q11.2 deletion were always offered either prenatally or postnatally. Clinical and echocardiographic examinations were performed in livebirths and a postmortem examination in cases of termination of pregnancy. Results: During the study period, 85 fetuses were diagnosed prenatally with RAA-no ICA. Genetic or clinical data were not available for three cases and these were excluded from analysis. 22q11.2 deletion was found in 7/82 cases (8.5% (95% CI, 3.8-17.3%)). The thymus was small or non-visualized in all seven cases and additional abnormal sonographic findings were present in four. Conclusion: 22q11.2 deletion is present in a clinically significant proportion of fetuses with a prenatal diagnosis of RAA-no ICA. In such cases, a detailed sonographic examination, with assessment of the thymus in particular, may be useful to further define the level of risk for 22q11.2 deletion.