22q11.2 deletion syndrome in Singapore (2000-2003): a case for active ascertainment

The 22q11 deletion syndrome (22q11DS) is associated with many congenital structural anomalies, notably cardiac defects (conotruncal anomalies) and velopharyngeal insufficiency, as well as neurodevelopmental and psychiatric findings in later life. Recent studies have tried to ascertain the true population incidence of this condition. However, this is difficult due to possible under-ascertainment from incomplete genetic testing in possible cases. The aim of this study is to investigate the local incidence and association of this deletion syndrome with other congenital structural anomalies, with emphasis on cardiac defects.

Data of 22q11 deletion cases born in 2000-2003 were retrieved from the Singapore National Birth Defects Registry (NBDR) and analysed. Data of congenital cardiac defect cases notified to NBDR in the same period were also retrieved and compared with the deletion cases.

There were a total of 17 cases of 22q11DS in the four-year period 2000-2003, giving an overall incidence of 1.02 per 10,000 live-births or one in 9,804 births. 94 percent (16/17 cases) were associated with other structural anomalies, and of these, 68.8 percent (11/16 cases) had single system anomalies. Cardiac anomalies were the most common (100 percent). The deletion contributed to 0.86 percent (one in 116 cases) of all cardiac defects born during the same period. A higher contribution of this deletion was noted for interrupted aortic arch (10 percent), pulmonary atresia (12.7 percent) and truncus arteriosus (11.1 percent).

In view of the high proportion of this deletion among certain cardiac defects, genetic testing should be made available to investigate the true burden and contribution of this deletion. As more genetic testing is done for this deletion, we are likely to see an increase in incidence, reflecting the true prevalence of this condition.