Prevalence of recurrent pathogenic microdeletions and microduplications in over 9500 pregnancies

Objectives: The implementation of chromosomal microarray analysis (CMA) in prenatal testing for all patients has not achieved a consensus. Technical alternatives such as Prenatal BACs-on-BeadsTM (PNBoBsTM) have thus been applied. The aim of this study was to provide the frequencies of the submicroscopic defects detectable by PNBoBsTM under different prenatal indications. Methods: A total of 9648 prenatal samples were prospectively analyzed by karyotyping plus PNBoBsTM and classified by prenatal indication. The frequencies of the genomic defects and their 95%CIs were calculated for each indication. Results: The overall incidence of cryptic imbalances was 0.7%. The majority involved the DiGeorge syndrome critical region (DGS). The additional diagnostic yield of PNBoBsTM in the population with a low a priori risk was 1/298. The prevalences of DGS microdeletion and microduplication in the low-risk population were 1/992 and 1/850, respectively. Conclusions: The constant a priori risk for common pathogenic cryptic imbalances detected by this technology is estimated to be ~0.3%. A prevalence higher than that previously estimated was found for the 22q11.2 microdeletion. Their frequencies were independent of maternal age. These data have implications for cell-free DNA screening tests design and justify prenatal screening for 22q11 deletion, as early recognition of DGS improves its prognosis.