False Negative NIPT Results: Risk Figures for Chromosomes 13, 18 and 21 Based on Chorionic Villi Results in 5967 Cases and Literature Review.

Diane Van Opstal,Joke Polak,Maarten F C M Knapen,Femke De Vries,Karin E M Diderich,Marieke Joosten,Robert-Jan H Galjaard,Malgorzata I Srebniak,Attie T J I Go,Lutgarde C P Govaerts,Cardi Van Den Berg

doi:10.1371/journal.pone.0146794

Abstract

Non-invasive prenatal testing (NIPT) demonstrated a small chance for a false negative result. Since the “fetal” DNA in maternal blood originates from the cytotrophoblast of chorionic villi (CV), some false negative results will have a biological origin. Based on our experience with cytogenetic studies of CV, we tried to estimate this risk. 5967 CV samples of pregnancies at high risk for common aneuplodies were cytogenetically investigated in our centre between January 2000 and December 2011. All cases of fetal trisomy 13, 18 and 21 were retrospectively studied for the presence of a normal karyotype or mosaicism < 30% in short-term cultured (STC-) villi. 404 cases of trisomies 13, 18 and 21 were found amongst 5967 samples (6,8%). Of these 404 cases, 14 (3,7%) had a normal or low mosaic karyotype in STC-villi and therefore would potentially be missed with NIPT. It involved 2% (5/242) of all trisomy 21 cases and 7.3% (9/123) of all trisomy 18 cases. In 1:426 (14/5967) NIPT samples of patients at high risk for common aneuploidies, a trisomy 18 or 21 will potentially be missed due to the biological phenomenon of absence of the chromosome aberration in the cytotrophoblast.

Highlights

The validation of non-invasive prenatal testing (NIPT) for fetal trisomy detection revealed that there is a small chance of a false positive and false negative result [1]
In order to study the risk for a biological false negative NIPT result involving the chromosomes 13, 18 and 21, we retrospectively investigated all chorionic villi (CV) cases of fetal trisomy 13, 18 and 21 that were found in our centre during a 12-year period (January 2000-December 2011)
Trisomy 21 (Table 2): 242 cases of fetal trisomy 21 were encountered among 5967 CV samples of which 5 (2.0%) showed karyotypically normal STC results (N = 3) or low-level mosaicism (N = 2)

Summary

Introduction

The validation of non-invasive prenatal testing (NIPT) for fetal trisomy detection revealed that there is a small chance of a false positive and false negative result [1]. The fact that cell free ‘fetal’ DNA in the maternal plasma fraction originates from the cytotrophoblast of chorionic villi (CV) explains at least a part of the discrepancies between NIPT results and the actual fetal karyotype [2,3,4]. False Negative NIPT Results: Figures from Chorionic Villi Cytogenetics doi:10.1371/journal.pone.0146794.g001. In order to understand the biological origin of false positive and false negative NIPT results, it is important to understand the cytogenetics of chorionic villi. The origin of the cells that are investigated in the cytogenetic preparations are essentially different in both techniques: cells in STC-villi are derived from the cytotrophoblast, the outer cell layer of CV, and those of LTC-villi are predominantly from the inner cell layer, the mesenchymal core (Fig 1). With NIPT, only DNA from the cytotrophoblast is investigated and the results will be comparable to those from STC-villi

Methods

Results

Conclusion