A rare case of NIPT discrepancy caused by the placental mosaicism of three different karyotypes, 47,XXX, 47,XX,+21, and 48,XXX,+21

Uniparental maternal tetrasomy X co-occurrence with paternal nondisjunction: investigation of the origin of 48,XXXX

Tetrasomy X or 48,XXXX is a rare sex chromosome aneuploidy. The parental origin of tetrasomy X in a female patient with developmental delay was analyzed; all four X chromosomes were derived from the mother, and there were no paternally derived sex chromosomes. This finding indicates a rare incidental co-occurrence of maternal and paternal nondisjunction or polysomy rescue. The mechanism of 48,XXYY, which is related to developmental delay in males, was analyzed for comparison.

Discrepancy between non-invasive prenatal testing result and fetal karyotype caused by rare confined placental mosaicism: A case report

BACKGROUND

Confined placental mosaicism (CPM) is one of the major reasons for discrepancies between the results of non-invasive prenatal testing (NIPT) and fetal karyotype analysis.

CASE SUMMARY

We encountered a primiparous singleton pregnant woman with a rare CPM consisting of 47,XY,+21; 47,XXY; and 46,XY, who obtained a false-positive result on NIPT with a high risk for trisomy 21. Copy-number variation sequencing on amniotic fluid cells, fetal tissue, and placental biopsies showed that the fetal karyotype was 47,XXY, while the placenta was a rare mosaic of 47,XY,+21; 47,XXY; and 46,XY.

CONCLUSION

The patient had a rare CPM consisting of 47,XY,+21; 47,XXY; and 46,XY, which caused a discrepancy between the result of NIPT and the actual fetal karyotype. It is important to remember that NIPT is a screening test, not a diagnostic test. Any positive result should be confirmed with invasive testing, and routine ultrasound examination is still necessary after a negative result.

Fetomaternal microchimerism and genetic diagnosis: On the origins of fetal cells and cell-free fetal DNA in the pregnant woman

During pregnancy several types of fetal cells and fetal stem cells, including pregnancy-associated progenitor cells (PAPCs), traffic into the maternal circulation. Whereas they also migrate to various maternal organs and adopt the phenotype of the target tissues to contribute to regenerative processes, fetal cells also play a role in the pathogenesis of maternal diseases. In addition, cell-free fetal DNA (cffDNA) is detectable in the plasma of pregnant women. Together they constitute the well-known phenomenon of fetomaternal microchimerism, which inspired the concept of non-invasive prenatal testing (NIPT) using maternal blood. An in-depth knowledge concerning the origins of these fetal cells and cffDNA allows a more comprehensive understanding of the biological relevance of fetomaternal microchimerism and has implications for the ongoing expansion of resultant clinical applications.

Next Generation Sequencing Based Non-invasive Prenatal Testing (NIPT): First Report From Saudi Arabia

Background: Non-invasive prenatal testing (NIPT) for aneuploidy in pregnant women screening has been recently established in Saudi Arabia. We aim from this study to report our experience in the implementation of this new technology in clinical practice and to assess factors influencing cell-free fetal (cffDNA) fraction and successful NIPT reporting.

Methods: In total, 200 pregnant women were subjected to the NIPT test using standard methods. Next-generation sequencing (NGS) was used to analyze cffDNA in maternal plasma.

Results: Out of the 200 NIPT cases, the average age of pregnant women was 35 ± 6 years (range: 21–48 years). The average cffDNA fraction of reported cases was 13.72% (range: 3–31%). Out of these 200 cases, 187 (93.5%) were at low risk, while 13 (6.5%) cases revealed high risk for aneuploidy. Among these chromosomal abnormalities, 7 (3.5%) cases of Down’s syndrome, 5 (2.5%) Edwards’ Syndrome, and only 1 case of (0.5%) Patau’s syndrome was observed. Out of the 13 high-risk cases, 2 (15.3%) were found in women below the age of 30.

Conclusion: This is the first study reporting the successful implementation of an in-house NIPT screening service in Saudi Arabia. Our data showed high accuracy and sensitivity to detect high-risk cases indicating the usefulness of such a technique as an alternative to invasive testing and (hopefully) will change the common screening practice for pregnant women in Saudi Arabia.

A rare case of NIPT discrepancy caused by the placental mosaicism of three different karyotypes, 47,XXX, 47,XX,+21, and 48,XXX,+21

Background

Placental mosaicism is one of the major reasons for noninvasive prenatal testing (NIPT) discrepancy. Herein, we discovered a rare case of placenta with complex karyotypes that caused false‐positive and false‐negative results in noninvasive prenatal testing.

Methods

Next‐generation sequencing (NGS) and Quantitative fluorescent polymerase chain reaction (QF‐PCR) were performed on the cord blood sample, fetal tissues, and eight placental biopsies. Fluorescent In Situ Hybridization (FISH) and karyotyping were also carried to confirm the fetal genome status.

Results

The results suggested that the fetal chromosome was 47,XXX and the placenta had three karyotypes of 48,XXX,+21, 47,XX,+21, and 47,XXX. QF‐PCR indicated that the extra chromosome 21 and chromosome X were all from the father. It is speculated that the zygote may have 48,XXX,+21 karyotype and trisomy rescue could be the main mechanism for the development of the homogeneous fetus and complex mosaic placenta.

Conclusion

Overall, the complicated nature of our case underlines the importance of discussing with parents the possibility of both atypical and discordant results during preconfirmatory amniocentesis counseling and consent.