Secondary findings from non-invasive prenatal testing for common fetal aneuploidies by whole genome sequencing as a clinical service.

OBJECTIVE To report secondary or additional findings arising from introduction of non-invasive prenatal testing (NIPT) for aneuploidy by whole genome sequencing as a clinical service. METHODS Five cases with secondary findings were reviewed. RESULTS In Case 1, NIPT revealed a large duplication in chromosome 18p, which was supported by arrayCGH of amniocyte DNA, with final karyotype showing mosaic tetrasomy 18p. In Case 2, a deletion in the proximal long arm of chromosome 18 of maternal origin was suspected and confirmed by arrayCGH of maternal white cell DNA. In Case 3, NIPT was negative for trisomies 21 and 18. In-depth analysis for deletions/duplications was requested when fetal structural anomalies were detected at routine scan. A deletion in the proximal long arm of chromosome 3 was found and confirmed by karyotyping. In Case 4, NIPT correctly predicted confined placental mosaicism with triple trisomy involving chromosomes X, 7 and 21. In Case 5, NIPT correctly detected a previously unknown maternal mosaicism for 45X. CONCLUSION Non-invasive prenatal testing is able to detect a wide range of fetal, placental and maternal chromosomal abnormalities. This has important implications on patient counseling when an abnormality is detected by NIPT.