Noninvasive prenatal screening and diagnosis of two fetuses with Williams syndrome in a cohort of 19,607 pregnancies.

Background: This study aimed to evaluate the efficiency of noninvasive prenatal screening (NIPS) technology in screening for microdeletions in the 7q11.23 region.
Methods: 19,607 pregnant women underwent NIPS in our hospital. Maternal peripheral cell-free foetal DNA (cffDNA) was routinely screened for aneuploidy by cffDNA enrichment and simultaneously analyzed for pathogenic copy number variants (CNVs). The Williams syndrome (WS) 7q11.23 region was targeted in this study. Chromosomal microarray analysis (CMA) was used to verify the screen-positive samples.
Results: The mean concentration of cffDNA before and after enrichment increased from 9.44% to 19.32%, with a statistically significant difference. Two out of 19,607 samples tested for CNVs were found to have a heterozygous deletion at the 7q11.23 region, indicating a high risk for WS. CMA results confirmed the 1.5 megabase (Mb) deletions at the 7q11.23 region in amniotic fluid samples. One of the two WS foetuses had a small left ventricle by ultrasound screening, and the other did not have a significant cardiovascular abnormality phenotype.
Conclusions: NIPS screening for Williams syndrome can be achieved by enriching cell-free foetal DNA and improving bioinformatic analysis algorithms.