Positive cell-free fetal DNA testing for trisomy 13 reveals confined placental mosaicism

Confined placental mosaicism with trisomy 13 complicated by severe preeclampsia: A case report and literature review

A 31-year-old primiparous woman underwent non-invasive prenatal testing. The result was trisomy 13 (T13) positive. The chromosome 13 t-statistics (Z-score) was significantly high. The result of amniocentesis was normal karyotype (46,XX). Detailed ultrasound showed no fetal structural abnormalities. We suspected T13 confined placental mosaicism (CPM) and observed the course naturally. From the late second trimester, severe fetal growth restriction manifested followed by proteinuria and hypertension, diagnosing her with preeclampsia (PE). At 35 + 5 weeks, emergent cesarean section was required, yielding a 1480 g female infant. We sampled five locations of chorionic villi in the placenta. T13 cells dominated cells with normal karyotypes in all parts and the rate of trisomic cells ranged from 57% to 96%, which were generally high rate. None developed PE in reported T13 CPM cases and this is the first case of PE. The dominancy of T13 cells can be associated with PE development.

Low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy 13 at amniocentesis in a pregnancy associated with a positive non-invasive prenatal testing (NIPT) result suspicious of trisomy 13, a chorionic villus sampling (CVS) result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

CASE REPORT

A 29-year-old, gravida 2, para 1, woman underwent amniocentesis at 20 weeks of gestation because of a positive NIPT result (Z-score = 20.9, positive ≥3) suspicious of trisomy 13 at 11 weeks of gestation and a CVS result of mosaic trisomy 13 at 14 weeks of gestation. At 14 weeks of gestation, CVS revealed the multiplex ligation-dependent probe amplification (MLPA) result of rea X,Y (P095) × 1, 13 (P095) × 3, 18,21 (P095) × 2/X,Y (P095) × 1, 13,18,21 (P095) × 2 and a karyotype of 48,XY,+13,+mar [9]/47,XY,+mar[16]. She was referred to the hospital for genetic counseling at 15 weeks of gestation, and cytogenetic analysis of parental blood revealed 47,XY,+mar in the father and 46, XX in the mother. Fluorescence in situ hybridization (FISH) analysis on the paternal blood showed that the extra dicentric marker was derived from chromosome 15 without the locus SNRPN (15q11.2), and the result was 47,XY,+mar.ish dic(15) (D15Z1++, SNRPN-, PML-)[20]. Amniocentesis at 20 weeks of gestation revealed a karyotype of 47,XY,+mar pat (20/20). Simultaneous interphase FISH analysis on uncultured amniocytes revealed 32% (32/100 cells) mosaicism for trisomy 13. Quantitative fluorescence polymerase chain reaction (QF-PCR) analysis using the DNA extracted from the parental bloods and uncultured amniocytes excluded uniparental disomy (UPD) 13. Prenatal ultrasound findings were normal. The woman was advised to continue the pregnancy, and a phenotypically normal 2708-g male baby was delivered at 38 weeks of gestation, The cord blood, umbilical cord and placenta had the karyotypes of 47,XY,+mar pat and did not have UPD 13. When follow-up at age two months, the neonate was phenotypically normal. FISH analysis on buccal mucosal cells detected 5.3% (5/95 cells) mosaicism for trisomy 13, compared with 0% in the normal control.

CONCLUSION

Low-level mosaic trisomy 13 at amniocentesis can be associated with a positive NIPT result suspicious of trisomy 13, a CVS result of mosaic trisomy 13, cytogenetic discrepancy in various tissues and a favorable fetal outcome.

The accuracy and feasibility of noninvasive prenatal testing in a consecutive series of 20,626 pregnancies with different clinical characteristics

BACKGROUND

To evaluate the accuracy and feasibility of noninvasive prenatal testing (NIPT) according to the results of NIPT and pregnancy outcomes with different indications.

METHODS

Between October 2014 and December 2020, 20,626 pregnant women who received NIPT were included in this study. The positive predictive value (PPV) of trisomy 21, 18, and 13 (T21, T18, T13), sex chromosome abnormalities (SCAs), other chromosomal aneuploidies, and chromosomal microdeletion/microduplication were calculated. The positive results of NIPT were confirmed by amniocentesis, Karyotype analysis, and chromosome microarray analysis (CMA).

RESULTS

In total, 263 positive cases (263/20,626, 1.28%) were detected by NIPT, of which T21, T18, and T13 were 69, 26, and 9 cases, respectively. Sex chromosome abnormalities (SCAs), other chromosomal aneuploidies, and copy number variants (CNVs) were 69, 12, and 38 cases, respectively. There were true positive in 49 of T21, 13 of T18, 1 of T13, 32 of SCAs, 1 of other chromosomal aneuploidies, and 15 of CNVs. The NIPT sensitivity of T21, T18, T13, SCAs, other chromosomal aneuploidies, and CNVs was all 100%, the specialty was 99.90%, 99.94%, 99.96%, 99.82%, 99.95%, 99.89%, and the PPV was 71.01%, 50.00%, 11.11%, 46.38%, 8.33%, 39.47%, respectively. The PPV was high in T21, moderate in T18 and SCAs, and low in T13 and other chromosomal abnormalities.

CONCLUSION

NIPT has high accuracy, specificity and and can effectively avoid the occurrence of birth defects, but it cannot replace prenatal diagnosis. The accuracy, specificity, and sensitivity of NIPT in detecting sex chromosomes, chromosome microdeletion/microduplication, and other chromosomal abnormalities should be improved.

Systematic analysis of the causes of NIPS sex chromosome aneuploidy false-positive results

OBJECTIVE

To investigate the underlying causes of false positives in NIPT of fetal sex chromosomal aneuploidies using fetal cell-free DNA from maternal plasma.

METHODS

In the present study, we focus on a cohort of 23,984 pregnancy cases with NIPT. Karyotyping and FISH analysis were employed to verify the NIPT detected false-positive results of fetal sex chromosomal aneuploidies, and a comparative CNV sequencing on positive and negative NIPT cases was uniquely performed to elucidate the underlying causes.

RESULTS

A total of 166 cases (0.69%) were identified as fetal sex chromosomal abnormalities, while 84 cases were found to be false-positive results possibly associated with maternal X chromosomal aneuploidies (n = 8), maternal X chromosomal structural abnormalities (n = 1), maternal CNVs (n = 4) as well as known placental mosaicism (n = 1). Furthermore, our study showed that the maternal chromosome CNV between 1-1.6 Mb was associated with false-positive NIPT results in sex chromosomal abnormalities.

CONCLUSION

Our research demonstrated the spectrum of factors causing false positives in NIPT of fetal sex chromosomal abnormalities based on a large cohort. The effective maternal CNV size cut-off identified in our study could integrate into bioinformatics algorithms for reducing the false-positive rate, however, further investigation is necessary to confirm this.

Assessment and Clinical Utility of a Non-Next-Generation Sequencing-Based Non-Invasive Prenatal Testing Technology

Background: Rolling-circle replication (RCR) is a novel technology that has not been applied to cell-free DNA (cfDNA) testing until recently. Given the cost and simplicity advantages of this technology compared to other platforms currently used in cfDNA analysis, an assessment of RCR in clinical laboratories was performed. Here, we present the first validation study from clinical laboratories utilizing RCR technology. Methods: 831 samples from spontaneously pregnant women carrying a singleton fetus, and 25 synthetic samples, were analyzed for the fetal risk of trisomy 21 (T21), trisomy 18 (T18) and trisomy 13 (T13), by three laboratories on three continents. All the screen-positive pregnancies were provided post-test genetic counseling and confirmatory diagnostic invasive testing (e.g., amniocentesis). The screen-negative pregnancies were routinely evaluated at birth for fetal aneuploidies, using newborn examinations, and any suspected aneuploidies would have been offered diagnostic testing or confirmed with karyotyping. Results: The study found rolling-circle replication to be a highly viable technology for the clinical assessment of fetal aneuploidies, with 100% sensitivity for T21 (95% CI: 82.35-100.00%); 100.00% sensitivity for T18 (71.51-100.00%); and 100.00% sensitivity for T13 analyses (66.37-100.00%). The specificities were >99% for each trisomy (99.7% (99.01-99.97%) for T21; 99.5% (98.62-99.85%) for T18; 99.7% (99.03-99.97%) for T13), along with a first-pass no-call rate of 0.93%. Conclusions: The study showed that using a rolling-circle replication-based cfDNA system for the evaluation of the common aneuploidies would provide greater accuracy and clinical utility compared to conventional biochemical screening, and it would provide comparable results to other reported cfDNA methodologies.

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.

Evaluation of the Z-score accuracy of noninvasive prenatal testing for fetal trisomies 13, 18 and 21 at a single center

OBJECTIVE

To assess the correlation between Z-scores of positive noninvasive prenatal testing (NIPT) results and the positive predictive value (PPV) of NIPT.

METHODS

Pregnancies with positive NIPT results at Guangzhou Women and Children's Medical Centre between July 2017 and May 2020 were included in this study. Fetal karyotyping or microarray analysis was provided to patients with abnormal NIPT results for confirmatory testing. Logistic regression analyses was applied to study the relationship between the Z scores and the PPV performance. The optimal cutoff values for indicating fetal common trisomies were obtained based on receiver operating characteristic (ROC) curve analysis, and then the PPV were calculated in pregnancies with positive NIPT results at Z-score greater than or equal to cutoff value and in patients with a Z-score between 3 and cutoff value respectively.

RESULTS

A total of 214 pregnancies with positive NIPT results for fetal common trisomies were validated by invasive prenatal diagnosis and follow up in this study. Of these, NIPT indicated trisomy 13 in 25 cases, trisomy 18 in 54 cases and trisomy 21 in 135 patients. Logistic regression analyses showed a significant association (p < 0.05) between the Z-scores and true positive results for T21 and T18. For T13, the significant association was not observed (p > 0.05). The ROC curve analysis showed that the optimal cutoff Z-score for indicating fetal trisomies 13, 18, and 21 were 6.889, 7.574 and 6.612 respectively, and the corresponding area under curve were 0.706, 0.916, and 0.954. In this cohort with abnormal NIPT results, the cutoff values revealed a sensitivity of 96.8% and a specificity of 90% for indicating trisomies 21, and a sensitivity of 88.9% and a specificity of 92.6% for trisomies 18. However, probably due to the sample size, the sensitivity and specificity for indicating trisomy 13 were lower (85.7% and 61.1%) than that for trisomies 21 and 18. The PPVs in pregnancies with positive NIPT results at Z-score greater than or equal to cutoff value were 99.18% (121/122) for trisomy 21, 92.31% (24/26) for trisomy 18 and 46.15% (6/13) for trisomy 13. In patients with a Z-score between 3 and cutoff Z-score, the PPV of NIPT for trisomies 21, 18, and 13 were 30.77% (4/13), 10.71% (3/28), and 8.33% (1/12) respectively. Moreover, by classifying Z scores as 3 ≤ Z < 5, 5 ≤ Z < 10, and Z ≥ 10, the majority of Z scores were above 10 with a PPV of 99% for T21 and just 5.2% were between 3 and 5 with a PPV of 14.3%. In contrast for T18, over a third of tests had Z scores between 3 and 5. The PPV in this group is just over 5%.

CONCLUSIONS

The present results show that the PPV performance of NIPT for fetal trisomies 13, 18, and 21 are closely associated with Z-score. The higher the Z-score, the greater the likelihood that the aneuploidy result is correct. Our experience in evaluating the Z-score accuracy of NIPT in this study could be of use in similar work.

Efficiency of non-invasive prenatal screening in pregnant women at advanced maternal age

Background

Non-invasive prenatal screening (NIPS) is widely used as the alternative choice for pregnant women at high-risk of fetal aneuploidy. However, whether NIPS has a good detective efficiency for pregnant women at advanced maternal age (AMA) has not been fully studied especially in Chinese women.

Methods

Twenty-nine thousand three hundred forty-three pregnant women at AMA with singleton pregnancy who received NIPS and followed-up were recruited. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), receiver operating characteristic (ROC) curves and the Youden Index for detecting fetal chromosomal aneuploidies were analyzed. The relationship between maternal age and common fetal chromosomal aneuploidy was observed.

Results

The sensitivity, specificity, PPV, NPV of NIPS for detecting fetal trisomy 21 were 99.11, 99.96, 90.98, and 100%, respectively. These same parameters for detecting fetal trisomy 18 were 100, 99.94, 67.92, and 100%, respectively. Finally, these parameters for detecting trisomy 13 were 100, 99.96, 27.78, and 100%, respectively. The prevalence of fetal trisomy 21 increased exponentially with maternal age. The high-risk percentage incidence rate of fetal trisomy 21 was significantly higher in the pregnant women at 37 years old or above than that in pregnant women at 35 to 37 years old. (Youden index = 37).

Conclusion

It is indicated that NIPS is an effective prenatal screening method for pregnant women at AMA.

Non-Invasive Prenatal Testing: Current Perspectives and Future Challenges

Fetal aneuploidies are among the most common causes of miscarriages, perinatal mortality and neurodevelopmental impairment. During the last 70 years, many efforts have been made in order to improve prenatal diagnosis and prenatal screening of these conditions. Recently, the use of cell-free fetal DNA (cff-DNA) testing has been increasingly used in different countries, representing an opportunity for non-invasive prenatal screening of pregnant women. The aim of this narrative review is to describe the state of the art and the main strengths and limitations of this test for prenatal screening of fetal aneuploidies.

Next-generation sequencing: a follow-up of 36,913 singleton pregnancies with noninvasive prenatal testing in central China

PURPOSE

To evaluate the noninvasive prenatal testing (NIPT) results of 36,913 cases in Jiangxi province of central China and explore its application value in prenatal screening and diagnosis.

METHODS

This retrospective analysis included 36,913 singleton pregnant women who underwent NIPT because of moderate-/high-risk pregnancy or voluntary requirements between January 2017 and December 2019 in our hospital. Chromosomal abnormalities such as trisomies 21, 18, and 13 (T21, T18, T13) and sex chromosome aneuploidies (SCAs) were judged by standard Z-score analysis. Positive NIPT results were confirmed by amniocentesis and karyotyping. Pregnancy outcomes were followed up via telephone interview.

RESULTS

A total of 1.01% (371/36,913) positive cases were detected by NIPT, comprising 137, 46, 31, and 157 cases of T21, T18, T13, and SCAs, respectively. A total of 116 of T21, 27 of T18, 13 of T13, and 51 of SCAs were confirmed to be true positive; all normal cases that had been followed up were verified to be true negative. The NIPT sensitivity in T21, T18, T13, and SCAs was 100.00% individually, whereas the specificity was 99.94% (36,488/36,509), 99.95% (36,579/36,598), 99.95% (36,594/36,612), and 99.72% (36,472/36,574), respectively. Furthermore, the negative predictive values of T21, T18, T13, and SCAs were all 100%, while the positive predictive values were 84.67%, 58.70%, 41.94%, and 33.33%, respectively.

CONCLUSION

NIPT is highly sensitive and has a low false positive rate in testing clinically significant fetal aneuploidies of general reproductive women. However, this technique cannot substitute for amniocentesis and karyotyping, and detailed genetic counseling is also essential for the high-risk group of NIPT.

A retrospective analysis the clinic data and follow-up of non-invasive prenatal test in detection of fetal chromosomal aneuploidy in more than 40,000 cases in a single prenatal diagnosis center

OBJECTIVE

To evaluate the efficacy of non-invasive prenatal test (NIPT) in the detection of chromosomal aneuploidy according to the follow-up information from a single prenatal diagnosis center.

METHODS

A total of 40,311 cases were retrospectively reviewed. The screening was performed using a BGI protocol, pre-test and post-test genetic counseling was provided, and the pregnancy outcomes were recorded. The results of NIPT and clinical follow-up data were analyzed together with the pregnancy outcomes, confirmatory testing results, and ultrasound findings.

RESULTS

Of the 40,311cases were includes in the study, successful follow-up was conducted in 468 (1.16%) cases with high risk, 225 (0.56%) cases with rare autosomal trisomy (RAT) and copy number variation (CNV). 39,572 (98.17%) cases with low risk and 623 (1.57%) cases of which were confirmed with adverse pregnancy outcomes. 46 (0.1%) cases with failed tests. Among them, 398 (84.7%) cases with high-risk results chose invasive testing, revealing 198 true positive cases. In cases with RAT and CNV results, 189 cases underwent invasive testing, revealing 5 cases RAT and 4 pathogenic CNVs.

CONCLUSIONS

NIPT appears to be effective in detecting the fetal chromosomal aneuploidies T21, T18 and SCAs, but it exist false positive/negative cases, unconfirmed high-risk cfDNA results, and the high false positive rate in cases with RAT and CNV results implied the limitations of this screening method. Our study showed the importance to associate cfDNA screening results with clinical follow-up data and provided information that may help with result interpretation, genetic counseling and the decision making in clinic.

The Clinical Utility of Non-invasive Prenatal Testing for Pregnant Women With Different Diagnostic Indications

Background

Our aim was to evaluate the clinical utility of non-invasive prenatal testing for pregnant women with different diagnostic indications.

Methods

In eight counties and districts of Yancheng, we studied 13,149 pregnant women with different indications who were offered NIPT for fetal screening, including for sex chromosomal aneuploidies (SCAs), rare autosomal trisomies (RATs), and subchromosomal copy number variations (CNVs). The purpose was to compare the detection of positive predictive values (PPVs) of different indications with the use of NIPT. The results were validated by karyotyping, chromosomal microarray analysis (CMA), or follow-up of pregnancy outcomes.

Results

13,149 maternal plasma samples were sequenced, among which 28 samples (0.2%) failed the sequencing quality control. The remaining 13,121 samples were analyzed, and birth follow-up missed 2,192 samples (16.7%). The PPVs of NIPT results for trisomy 21 (T21) and trisomy 18 (T18) and SCAs were 96.67, 63.64, and 31.34%, respectively. Among the advanced maternal age (AMA), serum screening high risk (SSHR), serum screening intermediate risk (SSIR), and voluntary screening (VS) groups, the PPVs for the common trisomies were 81.25, 85.71, 100, and 70%, respectively; the PPVs for total chromosomal abnormalities were 55.82, 65.22, 23.08, and 36.59%, respectively.

Conclusion

NIPT for T21 and T18 and SCAs screening were ideal, and the PPVs for trisomy 13 (T13), RATs, and CNVs were low. For the AMA and VS groups, NIPT could be used as a first-line screening program; for SSHR and SSIR groups, NIPT could be used as a second-line supplementary screening program.

No. 348-Joint SOGC-CCMG Guideline: Update on Prenatal Screening for Fetal Aneuploidy, Fetal Anomalies, and Adverse Pregnancy Outcomes

OBJECTIVE

To review the available prenatal screening options in light of the recent technical advances and to provide an update of previous guidelines in the field of prenatal screening.

INTENDED USERS

Health care providers involved in prenatal screening, including general practitioners, obstetricians, midwives, maternal fetal medicine specialists, geneticists, and radiologists.

TARGET POPULATION

All pregnant women receiving counselling and providing informed consent for prenatal screening.

EVIDENCE

Published literature was retrieved through searches of Medline, PubMed, and the Cochrane Library in and prior to March 2016 using an appropriate controlled vocabulary (prenatal diagnosis, amniocentesis, chorionic villi sampling, non-invasive prenatal screening) and key words (prenatal screening, prenatal genetic counselling). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English and published from January 1985 to May 2016. Searches were updated on a regular basis and incorporated in the guideline. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical speciality societies.

GUIDELINE UPDATE

Evidence will be reviewed 5 years after publication to determine whether all or part of the guideline should be updated. However, if important new evidence is published prior to the 5-year cycle, the review process may be accelerated for a more rapid update of some recommendations.

Clinical application of noninvasive prenatal screening for sex chromosome aneuploidies in 50,301 pregnancies: initial experience in a Chinese hospital

To evaluate the clinical performance of noninvasive prenatal screening (NIPS) for fetal sex chromosome aneuploidies (SCAs), pregnant women were recruited in this retrospective observational study. The NIPS test was undertaken using high-throughput gene sequencing. In total,50,301 pregnant women were analysed for demographic characteristics and medical history. Of them, 308 women (0.61%) had high risk for fetal SCAs, including 138 for 45,X, 111 for 47,XXY, 42 for 47,XXX, and 17 for 47,XYY. After the pre-test counselling, 182 participants chose to undergo invasive prenatal diagnosis, confirming 59 positive cases. The combined positive predictive value of NIPS was 32.42% (59/182), 18.39% (16/87), 44.4% (12/27), 39.29% (22/56), and 75% (9/12) for detecting SCAs, 45,X, 47,XXX, 47,XXY, and 47,XYY, respectively. NIPS can be a useful method to detect the fetal SCAs using high-throughput gene sequencing, though accuracy can still be improved, especially for 45,X. Although the value of NIPS compare favorably with those seen in traditional screening approaches for SCAs, it is important to highlight the limitations of NIPS while educating clinicians and patients.

A gradual change of chromosome mosaicism from placenta to fetus leading to T18 false negative result by NIPS

BACKGROUND

Noninvasive prenatal screening (NIPS) has higher sensitivity and specificity compared to traditional prenatal screening. Nevertheless, the discordant results between the NIPS and prenatal diagnosis were occasionally reported. In current study, we investigated the genetic basis of a T18 fetus with a discordant trisomy 5 (T5) positive and trisomy 18 (T18) negative NIPS result.

METHODS

NIPS was used to detect fetal DNA in maternal circulating plasma based on semiconductor sequencing platform. The aneuploidies of the fetus and different part of placental tissues were investigated by copy number variation sequencing (CNV-seq) and chromosome microarray analysis (CMA).

RESULTS

The positive result of T5 was detected for the pregnant woman in NIPS, while T18 was found in the fetal karyotyping analysis after amniocentesis. Furthermore, placental mosaicism of T5 and T18 was found by CNV-seq and CMA, which revealed the mosaic ratio of T5 was gradually increased from umbilical cord to the placenta center, while that of T18 was gradually decreased.

CONCLUSION

For the reason of cell-free fetal DNA (cff DNA) in the maternal circulation originates from trophoblast cells of placenta, the level of placental mosaicism could cause false negative NIPS result in multiple aneuploidies. The present study proved that a discordant T5 positive and T18 negative NIPS result was caused by placental mosaicism. This study highlights placental mosaicism as a significant risk factor for discordant NIPS results. The result will be helpful for genetic counseling and clinical management of such pregnant woman.

Biological explanations for discordant noninvasive prenatal test results: Preliminary data and lessons learned

OBJECTIVE

Maternal plasma cell-free DNA (cfDNA) analysis is a powerful screening tool for Down syndrome. In a pilot series, we examined biologic causes of discordance between the cfDNA test results and the fetal karyotype. We also explored the feasibility of obtaining trio biospecimens by using parental engagement.

METHODS

A convenience sample of women with discordant cfDNA results were recruited by their care providers. We provided shipping materials and instructions for biospecimen collection. Maternal, newborn, and placental samples were examined with droplet digital PCR.

RESULTS

Thirteen of 15 women successfully had biospecimens obtained remotely. High-quality DNA was extracted in 12 of 13 women. Presumed biologic etiologies for discordance were identified in 7 of 12 women: 3 cases from additional clinical review (male renal transplant, vanishing twin, and colon cancer) and 4 cases from additional laboratory investigation using droplet digital PCR (3 with confined placental mosaicism and 1 with true fetal mosaicism).

CONCLUSIONS

Understanding the biology behind cfDNA-fetal karyotype discordancy is useful for follow-up clinical care. Our study suggests that most cases could be resolved by using a trio biospecimen protocol and parental involvement. To improve accuracy, additional sequencing of biospecimens will be required.

Analysis of the accuracy of Z-scores of non-invasive prenatal testing for fetal Trisomies 13, 18, and 21 that employs the ion proton semiconductor sequencing platform

Background

Non-invasive prenatal testing (NIPT) is frequently being used to screen for trisomies 13, 18 and 21 for prenatal diagnosis. However, NIPT performs poorly when compared with invasive testing and thus should not be used to diagnose trisomies. The result of NIPT for an individual woman in most genome-wide methods is calculated as a Z-score. The aim of this study was to assess the correlation between Z-scores of NIPT results and the accuracy of non-invasive prenatal testing.

Results

We evaluated 108 pregnant women with positive NIPT results, which were validated through karyotype analysis of amniotic fluid puncture by means of sequencing, bioinformatics analysis, and follow-up. Utilizing the ion proton semiconductor sequencing platform, we report a performance evaluation of NIPT-positive results at Third Affiliated Hospital of Zhengzhou University of Henan Province, China, by classifying Z-scores as 3 ≤ Z<5, 5 ≤ Z < 9 and Z ≥ 9. The findings indicate that positive NIPT results at Z ≥ 9 have a higher accuracy compared with positive NIPT results at 5 ≤ Z < 9 and 3 ≤ Z<5.

Conclusions

The findings show that Z-scores of NIPT results are closely related to the accuracy of non-invasive prenatal testing. However, false-positive NIPT results at 3 ≤ Z<5 may occur due to confined placental mosaicism (CPM).

Performance of non-invasive prenatal testing for trisomies 21 and 18 in twin pregnancies

Background

Cell-free fetal DNA in maternal plasma represents a source of fetal genetic material that can be sampled noninvasively. There are ample studies confirming the accuracy of NIPT in singleton pregnancies, but there is still relatively little studies demonstrate the feasibility and clinical application of a NIPT for fetal aneuploidy screening in twin pregnancies.

Results

In this study, we have finished 432 twin pregnancies screening by NIPT. There were 4 double chorionic dichorionic diamniotic (DCDA) cases of true positive NIPT results, including 1of T18 and 3 of T21, and 1 monochorionic diamniotic (MCDA) cases of true positive NIPT results, including 1of T21. The combined false-positive frequency for trisomies 21, 18 was 0%. Furthermore, there were 2 cases of false positive NIPT results, including 1 of T7 and 1 of sex chromosome aneuploidy. There was no false negative case, which gave a combined sensitivity and specificity of 100 and 99.53% respectively.

Conclusion

Our study demonstrated NIPT performed well in the detection of trisomy 21 in twin pregnancy. It is feasible and clinical applicable of NIPT for fetal aneuploidy screening in twin pregnancies. But, it needs a large number of clinical samples to demonstrate the applicability of other chromosomal abnormalities besides trisomies 21 and 18 in both singleton pregnancies and twin pregnancies.

Have we done our last amniocentesis? Updates on cell-free DNA for Down syndrome screening

Prenatal aneuploidy screening changed significantly in 2012 when cell-free fetal deoxyribonucleic acid (DNA) was introduced as a noninvasive prenatal test. A noninvasive prenatal test detects cell free fragments of fetal DNA from the placenta circulating in maternal blood that coexist with cell-free DNA (cfDNA) of maternal origin. Using next-generation sequencing, the noninvasive prenatal test compares maternal and fetal cfDNA ratios for chromosomes of interest (i.e., 21, 18, 13, X, and Y) to assess chromosomal aneuploidy. Compared to traditional screening using ultrasound and serum markers, the noninvasive prenatal test has superior test characteristics, including a higher detection rate and positive predictive value, and a lower false-positive rate. The noninvasive prenatal test is already used for primary screening in high-risk women and is rapidly expanding to all women. Given its increasing use, understanding the noninvasive prenatal test's limitations is critical. Discordant results (i.e. noninvasive prenatal test is positive for aneuploidy with a normal fetal karyotype) can occur because of biological processes such as aneuploidy confined to the placenta, a vanished twin, maternal aneuploidy or maternal cancer. Use of the noninvasive prenatal test for screening beyond the most common aneuploidies is not recommended. The noninvasive prenatal test is a major advance in prenatal aneuploidy screening but it is not diagnostic and does not replace invasive testing (i.e. chorionic villous sampling or amniocentesis) for confirmation of fetal chromosomal disorders.

Non-invasive prenatal testing in detecting sex chromosome aneuploidy: A large-scale study in Xuzhou area of China

BACKGROUND

Cell-free fetal DNA are widely used in the prenatal genetic testing during recent years. In the present study, we tried to investigate the clinical practical feasibility of non-invasive prenatal testing (NIPT) for prenatal sex chromosome aneuploidy (SCA) analysis among pregnancies in Xuzhou area of China.

METHODS

Among a cohort of 8384 pregnancies, maternal plasma samples from our prenatal diagnosis center was subject to the analysis for SCA using NIPT detection. The cases with positive screening results by NIPT detection were validated on karyotyping analysis.

RESULTS

From 8384 clinical pregnancies, 64 cases exhibited abnormal results detected by NIPT, in which 34 cases were false positive verified by amniotic fluid puncture and chromosome karyotyping analysis. Twelve positive Turner syndrome (monosomy X) cases in NIPT was confirmed to be sex chromosome abnormal by karyotyping analysis, in which included 9 cases of monosomy X, 1 case of mosaic (45X/47XXX), and 2 cases of mosaic with 45X/45XY karyotype. Of those 9 cases with 47XXX, 5 cases were found to be true positive. Among the ten cases of Klinefelter's syndrome (47XXY) indicated by NIPT, 6 cases (60%) were true positive. Lastly, NIPT indicated 47XYY in 9 cases. Karyotyping analysis found six cases were 47XYY, and one case was mosaic (46XY/47XYY).

CONCLUSION

Our findings showed that the true positive rate for monosomy X was lower by NIPT detection, while prediction of other SCA was relatively accurate. Therefore, NIPT could be a potential method for SCA screening, while this technique needed to be further investigated.

A case of placental trisomy 18 mosaicism causing a false negative NIPT result

Background

The non-invasive prenatal testing that evaluates circulating cell free DNA, and has been established as an additional pregnancy test for detecting the common fetal trisomies 21, 18 and 13 is rapidly revolutionizing prenatal screening as a result of its increased sensitivity and specificity. However, false positive and false negative results still exist.

Case presentation

We presented a case in which the non-invasive prenatal testing results were normal at 15 gestational age (GA), but an ultrasound examination at 30GA showed that the fetus had heart abnormalities, and the third trimester ultrasound at 33GA noted multiple anomalies including a 3.0 mm ventricular septal defect. Along with cordocentesis at 33GA, the cord blood sample cytogenetics analysis showed a mos 47,XN,+18[61]/46,XN[39] T18 karyotype. Six placental biopsies confirmed that the chromosome 18 placenta chimerism ratio had changed from 33% to 72%. Ultimately, the pregnancy was interrupted at 34GA.

Conclusions

We presented this case to highlight the need to clearly explain false positive or false negative results to patients. We believe that this information will also influence the development of future diagnostic test methodologies.

Trisomy 13: Changing Perspectives

The diagnosis of trisomy 13 has been considered incompatible with life. Trisomy 13 is associated with a pattern of congenital anomalies and mental disabilities that make caring for these infants a challenge for both the family and health care professionals. The clinical management of trisomy 13 varies based on the organ systems involved. The current standard of care has been withholding intensive support and providing comfort care. Recent literature suggests there are improved outcomes in infants who receive intensive care at birth. In addition, case reports evaluating older children with trisomy 13 report that, although there are significant intellectual and psychomotor disabilities, these children do meet developmental milestones such as smiling in response to parents, sitting unassisted, and walking with a walker. This case review will include a discussion of the clinical course of an infant born with mosaic trisomy 13 where the parents requested intensive care.

Recent advances in prenatal genetic screening and testing

The introduction of new technologies has dramatically changed the current practice of prenatal screening and testing for genetic abnormalities in the fetus. Expanded carrier screening panels and non-invasive cell-free fetal DNA-based screening for aneuploidy and single-gene disorders, and more recently for subchromosomal abnormalities, have been introduced into prenatal care. More recently introduced technologies such as chromosomal microarray analysis and whole-exome sequencing can diagnose more genetic conditions on samples obtained through amniocentesis or chorionic villus sampling, including many disorders that cannot be screened for non-invasively. All of these options have benefits and limitations, and genetic counseling has become increasingly complex for providers who are responsible for guiding patients in their decisions about screening and testing before and during pregnancy.

Confined placental mosaicism and its impact on confirmation of NIPT results

Non-invasive prenatal testing (NIPT) has been widely used to screen for common aneuploidies since 2011. While NIPT is highly sensitive and specific, false positive results can occur. One important cause of false positive results is confined placental mosaicism (CPM). This can occur through a mitotic nondisjunction event or through aneuploidy rescue. CPM is usually associated with normal fetal outcomes, but has been associated with intrauterine growth restriction, pregnancy loss, or perinatal death in some cases. CPM may also be a marker for uniparental disomy. Given that NIPT can result in false positives, positive results should be confirmed with invasive testing before any irreversible procedure is performed. Whether to perform CVS or amniocentesis to confirm a positive NIPT result is controversial. While CVS can be performed earlier than amniocentesis, CPM can also cause false positive results. Our practice is to proceed with CVS, and to examine all cell lines using both an uncultured sample using fluorescence in situ hybridization (FISH) or short-term culture, as well as long-term culture of the sample. If the results all show aneuploidy, the results are reported to the patient. Otherwise, if the results are also mosaic, amniocentesis is recommended and analyzed by both FISH and karyotype. © 2016 Wiley Periodicals, Inc.

False Negative Cell-Free DNA Screening Result in a Newborn with Trisomy 13

Background. Noninvasive prenatal screening (NIPS) is revolutionizing prenatal screening as a result of its increased sensitivity, specificity. NIPS analyzes cell-free fetal DNA (cffDNA) circulating in maternal plasma to detect fetal chromosome abnormalities. However, cffDNA originates from apoptotic placental trophoblast; therefore cffDNA is not always representative of the fetus. Although the published data for NIPS testing states that the current technique ensures high sensitivity and specificity for aneuploidy detection, false positives are possible due to isolated placental mosaicism, vanishing twin or cotwin demise, and maternal chromosome abnormalities or malignancy. Results. We report a case of false negative cell-free DNA (cfDNA) screening due to fetoplacental mosaicism. An infant male with negative cfDNA screening result was born with multiple congenital abnormalities. Postnatal chromosome and FISH studies on a blood specimen revealed trisomy 13 in 20/20 metaphases and 100% interphase nuclei, respectively. FISH analysis on tissues collected after delivery revealed extraembryonic mosaicism. Conclusions. Extraembryonic tissue mosaicism is likely responsible for the false negative cfDNA screening result. This case illustrates that a negative result does not rule out the possibility of a fetus affected with a trisomy, as cffDNA is derived from the placenta and therefore may not accurately represent the fetal genetic information.

Cell-free DNA testing in a trisomy 21 pregnancy with confined placental mosaicism for a cell line with trisomy for both chromosomes 18 and 21

NIPT (noninvasive prenatal testing) detected trisomy for two chromosomes. One trisomy reflected the fetal karyotype, and the other resulted from CPM (confined placental mosaicism). This case illustrates that extensive cytogenetic analysis can be required to identify CPM, and that patients should be counseled regarding the possibility of discordant NIPT results.

The type of feto-placental aneuploidy detected by cfDNA testing may influence the choice of confirmatory diagnostic procedure

OBJECTIVES

Cell-free DNA (cfDNA) screening can provide false positive/negative results because the fetal fraction originates primarily from trophoblast. Consequently, invasive diagnostic testing is recommended to confirm a high-risk result. Currently, there is debate about the most appropriate invasive method. We sought to estimate the frequency in which a chorionic villus sampling (CVS) performed after a high-risk cfDNA result would require a follow-up amniocentesis due to placental mosaicism.

METHODS

Analyses of the frequencies of the different types of mosaicism involving cytotrophoblasts, for trisomies 21 (T21), 18 (T18), 13 (T13) and monosomy X (MX) among 52,673 CVS karyotypes obtained from cytotrophoblast, mesenchyme and confirmatory amniocentesis.

RESULTS

After a high-risk cfDNA result for T21, 18, 13 and MX, the likelihood of finding CVS mosaicism and need for amniocentesis is, respectively, 2%, 4%, 22% and 59%. When mosaicism is detected by CVS, the likelihood of fetal confirmation by amniocentesis is, respectively, 44%, 14%, 4% and 26%.

CONCLUSIONS

In cases of high-risk cfDNA results for T21/T18, CVS (combining cytotrophoblast and mesenchyme analysis) can be considered, but with the caveat of 2-4% risk of an inconclusive result requiring further testing. In high-risk results for MX/T13, amniocentesis would appear to be the most appropriate follow-up diagnostic test, especially in the absence of sonographic findings.

Recommended pre-test counseling points for noninvasive prenatal testing using cell-free DNA: a 2015 perspective

Noninvasive prenatal testing (NIPT) using cell-free DNA is being offered to an increasing number of women. Comprehensive pre-test counseling is complicated by emerging information about the benefits and limitations of testing, as well as the potential to detect incidental findings. Genetic counselors are trained to facilitate informed decision-making; however, not all centers have access to these professionals. To aid in the informed consent process, we have summarized key points to be included in discussions with patients who are considering NIPT.

Proof-of-principle rapid noninvasive prenatal diagnosis of autosomal recessive founder mutations

BACKGROUND

Noninvasive prenatal testing can be used to accurately detect chromosomal aneuploidies in circulating fetal DNA; however, the necessity of parental haplotype construction is a primary drawback to noninvasive prenatal diagnosis (NIPD) of monogenic disease. Family-specific haplotype assembly is essential for accurate diagnosis of minuscule amounts of circulating cell-free fetal DNA; however, current haplotyping techniques are too time-consuming and laborious to be carried out within the limited time constraints of prenatal testing, hampering practical application of NIPD in the clinic. Here, we have addressed this pitfall and devised a universal strategy for rapid NIPD of a prevalent mutation in the Ashkenazi Jewish (AJ) population.

METHODS

Pregnant AJ couples, carrying mutation(s) in GBA, which encodes acid β-glucosidase, were recruited at the SZMC Gaucher Clinic. Targeted next-generation sequencing of GBA-flanking SNPs was performed on peripheral blood samples from each couple, relevant mutation carrier family members, and unrelated individuals who are homozygotes for an AJ founder mutation. Allele-specific haplotypes were constructed based on linkage, and a consensus Gaucher disease-associated founder mutation-flanking haplotype was fine mapped. Together, these haplotypes were used for NIPD. All test results were validated by conventional prenatal or postnatal diagnostic methods.

RESULTS

Ten parental alleles in eight unrelated fetuses were diagnosed successfully based on the noninvasive method developed in this study. The consensus mutation-flanking haplotype aided diagnosis for 6 of 9 founder mutation alleles.

CONCLUSIONS

The founder NIPD method developed and described here is rapid, economical, and readily adaptable for prenatal testing of prevalent autosomal recessive disease-causing mutations in an assortment of worldwide populations.

FUNDING

SZMC, Protalix Biotherapeutics Inc., and Centogene AG.

Positive predictive value of non-invasive prenatal screening for fetal chromosome disorders using cell-free DNA in maternal serum: independent clinical experience of a tertiary referral center

BACKGROUND

Non-invasive prenatal screening (NIPS) for fetal chromosome abnormalities using cell-free deoxyribonucleic acid (cfDNA) in maternal serum has significantly influenced prenatal diagnosis of fetal aneuploidies since becoming clinically available in the fall of 2011. High sensitivity and specificity have been reported in multiple publications, nearly all of which have been sponsored by the commercial performing laboratories. Once results are returned, positive and negative predictive values (PPVs, NPVs) are the performance metrics most relevant to clinical management. The purpose of this report is to present independent data on the PPVs of NIPS in actual clinical practice.

METHODS

Charts were retrospectively reviewed for patients who had NIPS and were seen March 2012 to December 2013 in a tertiary academic referral center. NIPS results were compared to diagnostic genetic test results, fetal ultrasound results, and clinical phenotype/outcomes. The PPV was calculated using standard epidemiological methods. Correlation between screen results and both maternal age at delivery and gestational age at time of screening was assessed using Wilcoxon's rank sum test.

RESULTS

Of 632 patients undergoing NIPS, 92 % of tests were performed in one of the four major commercial laboratories offering testing. However, all four laboratories are represented in both the normal and abnormal results groups. There were 55 abnormal NIPS results. Forty-one of 55 abnormal NIPS results were concordant with abnormal fetal outcomes, 12 were discordant, and 2 were undetermined. The PPV for all conditions included in the screen was 77.4 % (95 % CI, 63.4 - 87.3). Of 578 patients with normal NIPS results, normal pregnancy outcome was confirmed for 156 (27 %) patients. This incomplete follow-up of normal NIPS results does not affect PPV calculations, but it did preclude calculations of sensitivity, specificity, and NPV. Maternal age at delivery was significantly lower for patients with abnormal discordant results, compared to patients with abnormal concordant results (P = 0.034). Gestational age at time of screening was not associated with concordance of screen results (P = 0.722).

CONCLUSIONS

The experience of using NIPS in clinical practice confirms that abnormal results cannot be considered diagnostic. Pre-test counseling should emphasize this. Diagnostic genetic testing should always be offered following abnormal NIPS results.

Clinical implementation of NIPT - technical and biological challenges

Non-invasive prenatal testing (NIPT) for fetal aneuploidy detection is increasingly being offered in the clinical setting. Whereas the majority of tests only report fetal trisomies 21, 18 and 13, genome-wide analyses have the potential to detect other fetal, as well as maternal, aneuploidies. In this review, we discuss the technical and clinical advantages and challenges associated with genome-wide cell-free fetal DNA profiling.

Non-invasive prenatal testing for trisomies 21, 18 and 13: clinical experience from 146,958 pregnancies

OBJECTIVES

To report the clinical performance of massively parallel sequencing-based non-invasive prenatal testing (NIPT) in detecting trisomies 21, 18 and 13 in over 140,000 clinical samples and to compare its performance in low-risk and high-risk pregnancies.

METHODS

Between 1 January 2012 and 31 August 2013, 147,314 NIPT requests to screen for fetal trisomies 21, 18 and 13 using low-coverage whole-genome sequencing of plasma cell-free DNA were received. The results were validated by karyotyping or follow-up of clinical outcomes.

RESULTS

NIPT was performed and results obtained in 146,958 samples, for which outcome data were available in 112,669 (76.7%). Repeat blood sampling was required in 3213 cases and 145 had test failure. Aneuploidy was confirmed in 720/781 cases positive for trisomy 21, 167/218 cases positive for trisomy 18 and 22/67 cases positive for trisomy 13 on NIPT. Nine false negatives were identified, including six cases of trisomy 21 and three of trisomy 18. The overall sensitivity of NIPT was 99.17%, 98.24% and 100% for trisomies 21, 18 and 13, respectively, and specificity was 99.95%, 99.95% and 99.96% for trisomies 21, 18 and 13, respectively. There was no significant difference in test performance between the 72,382 high-risk and 40,287 low-risk subjects (sensitivity, 99.21% vs. 98.97% (P = 0.82); specificity, 99.95% vs. 99.95% (P = 0.98)). The major factors contributing to false-positive and false-negative NIPT results were maternal copy number variant and fetal/placental mosaicism, but fetal fraction had no effect.

CONCLUSIONS

Using a stringent protocol, the good performance of NIPT shown by early validation studies can be maintained in large clinical samples. This technique can provide equally high sensitivity and specificity in screening for trisomy 21 in a low-risk, as compared to high-risk, population.

Cell-free DNA screening for fetal aneuploidy as a clinical service

Non-invasive prenatal testing (NIPT) through the analysis of cell free (cf)DNA is revolutionizing prenatal screening for fetal aneuploidy. Current methods used in clinical practice include shotgun massively parallel sequencing (s-MPS); targeted (t-MPS); and an approach that takes advantage of single nucleotide polymorphism (SNP) differences between mother and fetus. Efficacy of cfDNA testing for the common autosomal trisomies far exceeds that of conventional screening. Depending on the methodology used, reasons for discordancy between cfDNA results and fetal karyotype can include true fetal mosaicism, confined placental mosaicism, presence of a maternal karyotype abnormality, insufficient counting due to low fetal fraction, and a vanishing twin. Among the possible cfDNA strategies a Primary test has the highest performance but is expensive, while a Contingent cfDNA test can achieve high performance at a relatively low cost. Practicalities to be considered in the provision of testing include pretest counseling about the scope and accuracy of the testing, the interpretation of results when there is a low fetal fraction and follow-up studies for positive test results. The role of first trimester nuchal translucency measurement and conventional biochemical testing needs to be reassessed in the context of the use of cfDNA.

Noninvasive prenatal testing using a novel analysis pipeline to screen for all autosomal fetal aneuploidies improves pregnancy management

Noninvasive prenatal testing by massive parallel sequencing of maternal plasma DNA has rapidly been adopted as a mainstream method for detection of fetal trisomy 21, 18 and 13. Despite the relative high accuracy of current NIPT testing, a substantial number of false-positive and false-negative test results remain. Here, we present an analysis pipeline, which addresses some of the technical as well as the biologically derived causes of error. Most importantly, it differentiates high z-scores due to fetal trisomies from those due to local maternal CNVs causing false positives. This pipeline was retrospectively validated for trisomy 18 and 21 detection on 296 samples demonstrating a sensitivity and specificity of 100%, and applied prospectively to 1350 pregnant women in the clinical diagnostic setting with a result reported in 99.9% of cases. In addition, values indicative for trisomy were observed two times for chromosome 7 and once each for chromosomes 15 and 16, and once for a segmental trisomy 18. Two of the trisomies were confirmed to be mosaic, one of which contained a uniparental disomy cell line. As placental trisomies pose a risk for low-grade fetal mosaicism as well as uniparental disomy, genome-wide noninvasive aneuploidy detection is improving prenatal management.

Non-invasive prenatal testing for fetal aneuploidies in the first trimester of pregnancy

OBJECTIVES

To evaluate the feasibility of non-invasive prenatal testing (NIPT) of maternal plasma samples collected from pregnant Chinese women in early gestation, between 8 + 0 and 12 + 6 weeks' gestation.

METHODS

In this pilot study, 212 women with high-risk pregnancies were recruited at a single Chinese Hospital. Fetal aneuploidies associated with chromosomes 21, 18, 13, X and Y were detected by massively parallel sequencing of maternal plasma DNA samples. Invasive prenatal diagnosis by either chorionic villus sampling or amniocentesis and then karyotyping was offered to all women to confirm both positive and negative NIPT results. Fetal DNA fraction was also determined in male pregnancies, by the relative percentage of Y-chromosome sequences. All confirmed NIPT-negative pregnancies were followed up to birth and neonates were clinically evaluated for any symptoms of chromosomal disease.

RESULTS

Autosomal aneuploidies trisomy 21 (n = 2), 18 (n = 1) and 13 (n = 1) were detected by NIPT and confirmed by amniocentesis and karyotyping. There were one false-positive 45,X sample and two false-negative samples associated with fetal karyotypes 47,XXY and 45,X[16]/47,XXX[14]. In the 100 male pregnancies, the median fetal DNA fraction was 8.54% and there was a trend towards an increasing fetal fraction from 8 + 0 to 12 + 6 weeks' gestation. The majority (95%) of pregnancies had a fetal DNA fraction > 4%, which is generally the limit for accurate aneuploidy detection by NIPT. Across this early gestational time period, there was a weak inverse relationship (R(2)  = 0.186) between fetal DNA fraction and maternal weight.

CONCLUSIONS

NIPT is highly reliable and accurate when applied to maternal DNA samples collected from pregnant women in the first trimester between 8 + 0 and 12 + 6 weeks.

Ethical issues in DNA sequencing in the neonate

With the recognition of genetic disorders in the newborn, there is the potential to offer new lifesaving therapies. For other conditions such as hypothyroidism in Down syndrome or hypercalemia in the 22q11 microdeltion syndrome, the early identification of an untreatable condition permits prompt screening for potential comorbid conditions. DNA testing for disorders and DNA-based screening are rapidly evolving. With new more powerful tests, there is an increasing ability to see into a potential future and change the outcome for newborns. However, there remain significant ethical and structural issues to be considered before routine implementation of DNA testing.

Chromosomale Mosaike in der klinischen Zytogenetik

In der Zytogenetik werden Zellen im Gegensatz zu molekulargenetischen Untersuchungen individuell analysiert. Dadurch können Zellen mit verschiedenen Karyotypen (Zellmosaike) aufgedeckt werden. Dieser Beitrag gibt einen Überblick über die verschiedenen Probleme der diagnostischen Befunderhebung und -interpretation chromosomaler Mosaike. Eine besondere Herausforderung liegt darin, dass zwischen echten Mosaiken einerseits und Kulturartefakten, Pseudomosaiken, Alterseffekten, mütterlicher Kontamination oder Chimärismus andererseits unterschieden werden muss. Die Wahrscheinlichkeit, ein chromosomales Mosaik in der zytogenetischen Routinediagnostik zu übersehen, ist sehr hoch, da hier nur ca. 15 von 1012 Körperzellen und dazu in der Regel nur ein einziger Gewebetyp untersucht werden. Einige zytogenetische Mosaike sind typisch für bestimmte Syndrome, wie z. B. das Pallister-Killian-, das Katzenaugen oder das Ullrich-Turner-Syndrom; andere sind charakteristisch für bestimmte Krankheitsbilder, einschließlich hämatologischer maligner Erkrankungen.

Counseling Challenges with Variants of Uncertain Significance and Incidental Findings in Prenatal Genetic Screening and Diagnosis

Prenatal genetic screening and testing provides prospective parents information about the health of their fetus. It is offered to find or address an increased risk for chromosomal abnormalities or other genetic conditions in the fetus or to identify the cause of fetal structural abnormalities detected by prenatal imaging. Genome-wide tests, such as the already widely-used chromosomal microarray analysis and emerging diagnostic whole exome and whole genome sequencing, have improved the ability to detect clinically significant findings, but have also increased the chance of detecting incidental findings and variants of uncertain significance. There is an extensive ongoing discussion about optimal strategies for diagnostic laboratories to report such findings and for providers to communicate them with patients. While consensus opinions and guidelines are beginning to appear, they often exclude the prenatal setting, due to its unique set of challenging considerations. These include more limited knowledge of the impact of genetic variants when prospectively detected in an ongoing pregnancy, the absence or limitations of detecting clinically recognizable phenotypes at the time of testing and the different decision-making processes that will ensue from testing. In this review, we examine these challenges within the medical ethical framework unique to prenatal care.