Molecular genetic analysis reveals atypical confined placental mosaicism with a small supernumerary marker chromosome derived from chromosome 18: A clinical report of discordant results from three prenatal tests

Prenatal Identification of Confined Placental Mosaicism in Pregnant Women with Fetal Growth Restriction

We examined the influence of confined placental mosaicism (CPM) as a cause of fetal growth restriction (FGR), and whether CPM can be screened using cell-free DNA (cfDNA) analysis of the maternal plasma. We analyzed cfDNA in the maternal plasma of 40 FGR cases with an estimated fetal weight of less than - 2.0 SD using massively parallel sequencing to detect chromosomal aberrations. Fetal and placental genotyping was performed to confirm CPM cases. cfDNA analyses of maternal plasma detected suspected CPM cases with chromosomal aneuploidy or copy number variations in 5 of 40 cases (12.5%). For 4 cases in which the entire placenta consisted of cells with chromosomal abnormalities, fetal growth was severely restricted. CPM can be screened by cfDNA analysis in maternal plasma, accounting for approximately 10% of the causes of moderate or severe FGR, and the higher the proportion of abnormal karyotype cells in the placenta, the more severe the placental dysfunction and FGR.

Direct Assessment of Single-Cell DNA Using Crudely Purified Live Cells: A Proof of Concept for Noninvasive Prenatal Definitive Diagnosis

Noninvasive testing techniques are often used for fetal diagnosis of genetic abnormalities but are limited by certain characteristics, including noninformative results. Thus, novel methods of noninvasive definitive diagnosis of fetal genetic abnormalities are needed. The aim of this study was to develop a single-cell DNA analysis method with high sensitivity and specificity that enables direct extraction of genetic information from live fetal cells in a crude mixture for simultaneous evaluation. Genomic DNA from circulating fetal CD45^-CD14^- cells, an extremely rare cell type, extracted from 10-mL samples of maternal peripheral blood, was extracted using a single-cell-based droplet digital (sc-dd) PCR system with a modified amount of polymerase. A hexachloro-6-carboxyfluorescein-labeled RPP30 probe was used as an internal control and a 6-carboxyfluorescein-labeled SRY probe as a target. The results indicated that no droplets generated with samples from pregnant women carrying female fetuses were positive for both probe signals, whereas droplets prepared with samples from pregnant women carrying male fetuses were positive for both probe signals. The latter was considered a direct assessment of genetic information from single circulating male fetal cells. Thus, the modified sc-ddPCR system allows the detection of genetic information from rare target cells in a crudely purified cell population. This research also serves as a proof of concept for noninvasive prenatal definitive diagnosis.

Retrospective details of false-positive and false-negative results in non-invasive prenatal testing for fetal trisomies 21, 18 and 13

OBJECTIVE

Maternal characteristics and neonatal outcomes associated with cell-free DNA (cfDNA) results were analysed retrospectively to assess the details of false-positive and false-negative results after initial blood sampling in non-invasive prenatal testing (NIPT).

STUDY DESIGN

A multicentre retrospective study was performed for women undergoing NIPT who received discordant cfDNA results between April 2013 and March 2018. The NIPT data obtained using massive parallel sequencing were studied in terms of maternal background, fetal fraction, z-scores, invasive procedure results and neonatal outcomes after birth.

RESULTS

Of the 56,545 women who participated in this study, 54 false-positive (0.095 %) and three false-negative (0.006 %) cases were found. Seven of the 54 false-positive cases (13.0 %) had vanishing twin on ultrasonography. Among the 18 false-positive cases of trisomy 18, confined placental mosaicism (CPM) was confirmed in three cases (16.7 %), while CPM was present in one of the three false-negative cases of trisomy 21.

CONCLUSION

These data suggest that the incidence of women with false-positive or false-negative results is relatively low, that such false results can often be explained, and that vanishing twin and CPM are potential causes of NIPT failure. Genetic counselling with regard to false results is important for clients prior to undergoing NIPT.