A rare Down syndrome foetus with de novo 21q;21q rearrangements causing false negative results in non-invasive prenatal testing: a case report

Two cases of placental trisomy 21 mosaicism causing false-negative NIPT results

BACKGROUND

Non-invasive prenatal testing (NIPT) using cell-free DNA has been widely used for prenatal screening to detect the common fetal aneuploidies (such as trisomy 21, 18, and 13). NIPT has been shown to be highly sensitive and specific in previous studies, but false positives (FPs) and false negatives (FNs) occur. Although the prevalence of FN NIPT results for Down syndrome is rare, the impact on families and society is significant.

CASE PRESENTATION

This article described two cases of foetuses that tested "negative" for trisomy 21 by NIPT technology using the semiconductor sequencing platform. However, the fetal karyotypes of amniotic fluid were 46,XY, + 21 der(21;21)(q10;q10) and 47,XY, + 21 karyotypes, respectively. Placental biopsies confirmed that, in the first case, the chromosome 21 placenta chimerism ratio ranged from 13 to 88% with the 46,XX, + 21,der(21;21)(q10;q10)[86]/46,XX[14] karyotype of placental chorionic cells (middle of fetal-side placental tissue). However, in the second case, of all the placental biopsies, percentage of total chimerism was less than 30%; and placental biopsies taken at the middle of maternal side and middle of fetal side, also had variable trisomy 2 mosaicism levels of 10% and 8%, respectively. Ultimately, the pregnancies were interrupted at 30 gestational age (GA) and 27GA, respectively.

CONCLUSIONS

In this study, we present two cases of FN NIPT results that might have been caused by biological mechanisms, as opposed to poor quality, technical errors, or negligence. Clinical geneticists and their patients must understand that NIPT is a screening procedure.

Parental Psychological Distress of Missed Diagnosis of Down Syndrome at Antenatal Screening: A Rare, but Still Real Occurrence - A Case Report and Review of Literature

INTRODUCTION

Prenatal screening programs are important components for pregnant women care and are often linked with grief and shock based on gestational age or the diagnosis. Lower/no sensitivity is also associated with these screening programs leading to providing false-negative outputs.

CASE PRESENTATION

Present work shows a case of missed antenatal diagnosis of Down syndrome and its persistant medical and psychological impact on the family members. We have also discussed the relevant economic and medical-legal issues related to the context and aimed to maintain an adequate awareness among healthcare to discuss properly these investigations (difference between screening and diagnostic testing), their possible outcome (chances of false results) and enabled the pregnant women/couple to take informed decision on early pregnancy.

CONCLUSION

These programs are considered as routine clinical practice in many countries from last few years and are necessary to assess the pros and cons of these programs. One of the prime cons involves the likeliness of obtaining a false-negative result due to lack of 100% sensitivity and specificity.

The application of expanded noninvasive prenatal screening for genome-wide chromosomal abnormalities and genetic counseling

OBJECTIVE

To evaluate the clinical application of expanded noninvasive prenatal screening (eNIPS) for genome-wide large copy number variation (CNV), i.e. chromosomal deletion/duplication >5 Mb, and aneuploidy; also to provide practical information for counseling eNIPS positive cases.

METHOD

We recruited 34,620 women with singleton pregnancy for genome-wide cell-free plasma DNA sequencing. Screening positive cases were verified by karyotyping and/or SNP array.

RESULT

A total of 461 (1.33%) positive cases were identified through our cfDNA screening including 209 cases of common trisomies (0.60%), 124 cases of sex chromosomal abnormalities (SCA) (0.36%), 71 cases of other autosomal anueploidies (OAA) (0.21%), and 57 CNVs larger than 5 Mb (0.16%). The predictive positive values (PPV) were 70.06% in general for common trisomies with as high as 91.67% for Trisomy21 (T21), 40.22% in general for SCAs with as high as 100% for Jacob Syndrome (XYY). The PPV for OAAs was 5.45%, and T7/T8/T16/T22 were the most frequent OAAs (n = 15, 9, 9, 8, respectively). The PPV for CNVs larger than 5 Mb was 51.22% (n = 57) with the CNV mostly detected on Chr5/Chr4/Chr2/Chr7 (n = 10, 8, 5, 5, respectively).

CONCLUSION

The expanded NIPS had shown promising PPVs for CNVs (large than 5 Mb), SCAs and common trisomies, yet this method required higher efficacy in screening for OAAs. The post-test genetic counseling for expanded NIPS should be tailored to the types of positive cases and also address the origin of abnormal signals (fetal vs. maternal).