Analysis of tissue from products of conception and perinatal losses using QF-PCR and microarray: A three-year retrospective study resulting in an efficient protocol

From chromosomal aberrations to mutations in individual genes - the significance of genetic studies of chorions after miscarriage in the search for causes of miscarriages

OBJECTIVE

To determine the frequency of chromosomal aberrations in chorions after a miscarriage. The second was to examine selected euploid chorions using a next-generation sequencing (NGS) panel designed to assess 43 genes associated with pregnancy loss.

MATERIALS AND METHODS

The 1244 chorions were tested by targeted quantitative fluorescent PCR (QF-PCR, 827 chorions) and microarray-based comparative genomic hybridization (aCGH, 417 chorions). Then, 9 euploid chorions were examined using a designed NGS panel.

RESULTS

Trisomies were the most common chromosomal aberration identified in the spontaneous miscarriage samples. The second chromosomal abnormality in the aCGH group and the third most common in the QF-PCR group was monosomy X. Structural aberrations were the third most common aberration in the samples screened by aCGH (7.7% of chorions). In 19% of 647 couples who submitted chorions for analysis after pregnancy loss, the chromosomal abnormality in the chorion originated from a woman with a balanced chromosomal rearrangement. This discovery was statistically significant compared to patients with normal chorions. Using the designed NGS panel, we identified a potentially pathogenic de novo variant in the F5 gene in two euploid chorions. Additionally, among the patients who experienced miscarriages and were screened using the NGS panel, we identified variants in the MDM, ACE, and NLRP2 genes that could be associated with a predisposition to pregnancy loss.

CONCLUSION

Numerical aberrations are the most common cause of miscarriages, but structural chromosomal aberrations also account for a significant proportion of abnormal results. Our findings indicate that couples with structural chromosomal abnormalities in material post-miscarriage are at increased risk of carrying balanced chromosomal abnormalities. Moreover, NGS-based analyses can uncover previously unidentified causes of miscarriages in the chorionic villi.

A New Stepwise Molecular Work-Up After Chorionic Villi Sampling in Women With an Early Pregnancy Loss

Objective: To explore the use of a new molecular work-up based on the stepwise use of Quantitative Fluorescence PCR (QF-PCR) extended to eight chromosomes and single nucleotide polymorphism array (SNP-array) in chorionic villi obtained by chorionic villi sampling (CVS) offered to women experiencing an early pregnancy loss.

Methods: During a 3-year period (January 2016–December 2018), CVS was offered to women experiencing an early pregnancy loss before the evacuation of the products of conception (POC) to retrieve chorionic villi, irrespective of the number of previous losses. A new molecular work-up was prospectively assayed encompassing a first QF-PCR round (with the 21, 18, 13, 7, X, and Y chromosomes), a second QF-PCR round (with the 15, 16, and 22 chromosomes), and a high resolution SNP-array in those cases with normal QF-PCR results. A control group in which POC were collected after surgical uterine evacuation was used to be compared with the intervention group.

Results: Around 459 women were enrolled in the intervention group (CVS) and 185 in the control group (POC after uterine evacuation). The QF-PCR testing success rates were significantly higher in the intervention group (98.5%: 452/459) as compared to the control group (74%: 109/147; p < 0.001), while the chromosomal anomaly rate at the two QF-PCR rounds was similar between the two groups: 52% (234/452) in the intervention and 42% (46/109) in the control group (p = 0.073). The SNP-array was performed in 202 QF-PCR normal samples of the intervention group and revealed 67 (33%) atypical chromosomal anomalies (>10 Mb), 5 (2.5%) submicroscopic pathogenic copy number variants, and 2 (1%) variant of uncertain significance (VOUS).

Conclusion: Eighty-two percent of women experiencing an early pregnancy loss opted for a CVS. The testing success rates were higher in the intervention group (CVS; 98%) as compared to the control group (POC; 74%). The overall yields were 52% by QF-PCR (including three complete hydatiform moles), and 16% by SNP-array, including 15% atypical chromosomal anomalies and 1.1% submicroscopic pathogenic copy number variants.

Analysis of tissue from pregnancy loss and aborted fetus with ultrasound anomaly using subtelomeric MLPA and chromosomal array analysis

OBJECTIVE

To evaluate the incidence and types of chromosomal abnormalities in pregnancy loss and aborted fetuses with anomaly and compare the performance of subtelomeric MLPA and chromosomal microarray analysis (CMA) in these specimens.

METHODS

Samples were collected from spontaneous miscarriages, stillbirths and aborted fetuses with anomaly between January 2015 and April 2019. Chromosomal abnormalities were detected using subtelomeric MLPA and CMA.

RESULTS

Among the 172 miscarriage samples, CMA detected pathogenic chromosomal abnormalities in 88 cases. MLPA could identified all aneuploidies and most pathogenic CNVs, missing all polyploidies; Of the 30 stillbirths, one pathogenic CNV and two VOUS were identified by CMA, all of which were missed from MLPA; Of the 135 aborted fetuses with anomaly, CMA identified pathogenic chromosomal abnormalities in 32 fetuses (23.7%); 18.95% in fetuses with isolated, and 35% in fetuses with multiple anomalies. MLPA can identify all aneuploidies but missing most pathogenic CNVs.

CONCLUSION

Our systematical comparison of subtelomeric MLPA and CMA for chromosomal analysis of tissue from pregnancy loss and aborted fetuses with anomaly is useful for assessing clinical utility of these techniques. MLPA screening, coupled with CMA analysis, is a cost-effective approach to detect chromosomal abnormalities in miscarriage and anomalous fetuses. However, MLPA might not be appropriate for chromosome analysis in stillbirth without structural anomaly; further research with more samples is needed.

Clinical Utility of a High-Resolution Melting Test for Screening Numerical Chromosomal Abnormalities in Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) occurs in approximately 5% of clinically identified pregnancies. Determining the cause of RPL is essential. Genetic testing, accompanied by an evidence-based workup, is the well-accepted process for evaluating RPL; however, current genetic tests have limitations in clinical practice. We, thus, developed a high-resolution melting analysis-based test (HRM test) to screen for the most common numerical chromosomal abnormalities present in the products of conception. We examined 765 products-of-conception samples with known karyotypes retrospectively using the HRM test, which showed high technical sensitivity (96.1%) and specificity (96.3%) as well as a high positive predictive value (95.9%) for the screening of chromosomal abnormalities. The cost-effectiveness of four RPL evaluation strategies that employ different genetic tests, karyotyping, chromosomal microarray/next-generation sequencing, the HRM test, and a combination of the HRM test and chromosomal microarray/next-generation sequencing, was then compared. The costs of diagnosing an explained RPL using karyotyping or the HRM test alone were similar. Performance of the HRM screening test before chromosomal microarray/next-generation sequencing analysis improved cost-effectiveness by approximately 30%. Cost-effectiveness was more prominent in the advanced maternal age group. Thus, the HRM test could be used as an initial screening tool, followed by other diagnostic methods to improve the cost-effectiveness of RPL evaluation, or as an alternative genetic test when other methods are unavailable or unaffordable.

Combination of QF-PCR and aCGH is an efficient diagnostic strategy for the detection of chromosome aberrations in recurrent miscarriage

Background

Our aim was to conduct a comprehensive genetic evaluation using the combination of QF‐PCR (quantitative fluorescence polymerase chain reaction) and aCGH (array comparative genomic hybridization) for the detection of the frequency and type of chromosome aberrations in recurrent miscarriage (RM) in the clinical setting.

Methods

This retrospective study was conducted on 73 first‐trimester products of conception (POC) between September 2014 and February 2017. The POCs were collected from 73 women with at least one previous miscarriage and analyzed for chromosomal anomalies using QF‐PCR and aCGH as part of the routine clinical evaluation.

Results

Chromosome aberrations were detected in 52/73 POCs (71.2%), of which 41 (56.2%) were identified by QF‐PCR and an additional 11 (15.1%) by aCGH. Numerical aberrations constituted 92.3% of abnormalities, with trisomies as the most common subtype (72.9%). Causative structural aberrations were found in three samples (5.8%). The frequency of chromosome aberrations was not dependent on the number of previous miscarriages, whereas it significantly increased with advanced maternal age.

Conclusion

Our results confirm that chromosome aberrations are the most common cause of RM and that QF‐PCR and aCGH combination should be included in the routine genetic analysis of POCs of couples with miscarriage.

Chromosomal aberrations in pregnancy and fetal loss: Insight on the effect of consanguinity, review of 1625 cases

Background

Pregnancy loss affects 10%–15% of pregnancies and is caused by several factors, maternal and fetal. Most common cause is chromosomal aneuploidy and has traditionally been detected by karyotyping product of conception and/or fetal tissue. In recent years, array comparative genomic hybridization (a‐CGH) has been used because of its higher detection and lower failure rates.

Methods

DNA was extracted from 1625 products of abortion or fetal tissue. In 1,104 cases both quantitative fluorescent‐polymerase chain reaction (QF‐PCR) and a‐CGH, and in 521 cases only a‐CGH, was performed.

Results

The detection rate using QF‐PCR and a‐CGH is 20% compared to 12.7%, overall, and 15.7%, excluding failed samples, by karyotypes in our center. QF‐PCR and a‐CGH failed in 1.9% of cases, while the failure rate for karyotypes was 20.1%. The difference of detection and failure rates is significant (p‐value < 0.001 and p‐value < 0.001 respectively). Unexpectedly we also found a significant difference in frequency of imbalances in related versus unrelated couples. (χ² = 11.4926, p‐value < 0.001).

Conclusion

It is highly likely that the pregnancy loss in consanguineous couples is caused by other genetic and immune mechanisms. It is plausible that, through the same mechanism by which single gene disorders have a higher prevalence of manifesting disease in consanguineous couples, they can cause lethal genetic disorders leading to pregnancy loss and intra‐uterine fetal death (IUFD) in these couples. Our findings suggest that this is a matter for further study as it will greatly influence the approach to counseling and managing consanguineous couples with pregnancy loss.

Added value of chromosomal microarray analysis over karyotyping in early pregnancy loss: systematic review and meta-analysis

OBJECTIVE

To estimate the increased test success rate and incremental yield of chromosomal microarray analysis (CMA) over conventional karyotyping in detection of pathogenic copy number variants (CNVs) and variants of unknown significance (VOUS) in early pregnancy loss.

METHOD

This was a systematic review conducted in accordance with PRISMA criteria. All articles identified in PubMed, Ovid MEDLINE and Web of Science, between January 2000 and April 2017, that described CNVs in early pregnancy losses (up to 20 weeks) were included. Risk differences were pooled to estimate the incremental yield of CMA over karyotyping overall, and after stratification. In addition, test success rate, defined as the proportion of informative results, was compared in series in which CMA and karyotyping were performed concurrently.

RESULTS

Twenty-three studies, reporting on 5507 pregnancy losses up to 20 weeks with full data available, met the inclusion criteria for analysis. In the series in which CMA and karyotyping were performed concurrently, CMA showed a significant improvement in success rate, providing informative results in 95% (95% CI, 94-96%) of cases compared with karyotyping in which informative results were provided in 68% (95% CI, 66-70%) of cases. Combined data from reviewed studies revealed that incremental yields of CMA over karyotyping were 2% (95% CI, 1-2%) for pathogenic CNVs and 4% (95% CI, 3-6%) for VOUS. The most common pathogenic CNVs reported were 22q11.21 and 1p36.33 deletion.

CONCLUSION

In comparison with conventional karyotyping, CMA provides a significant increase in test success rate and incremental diagnostic yield in early pregnancy loss. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Practice guideline: joint CCMG-SOGC recommendations for the use of chromosomal microarray analysis for prenatal diagnosis and assessment of fetal loss in Canada

Background

The aim of this guideline is to provide updated recommendations for Canadian genetic counsellors, medical geneticists, maternal fetal medicine specialists, clinical laboratory geneticists and other practitioners regarding the use of chromosomal microarray analysis (CMA) for prenatal diagnosis. This guideline replaces the 2011 Society of Obstetricians and Gynaecologists of Canada (SOGC)-Canadian College of Medical Geneticists (CCMG) Joint Technical Update.

Methods

A multidisciplinary group consisting of medical geneticists, genetic counsellors, maternal fetal medicine specialists and clinical laboratory geneticists was assembled to review existing literature and guidelines for use of CMA in prenatal care and to make recommendations relevant to the Canadian context. The statement was circulated for comment to the CCMG membership-at-large for feedback and, following incorporation of feedback, was approved by the CCMG Board of Directors on 5 June 2017 and the SOGC Board of Directors on 19 June 2017.

Results and conclusions

Recommendations include but are not limited to: (1) CMA should be offered following a normal rapid aneuploidy screen when multiple fetal malformations are detected (II-1A) or for nuchal translucency (NT) ≥3.5 mm (II-2B) (recommendation 1); (2) a professional with expertise in prenatal chromosomal microarray analysis should provide genetic counselling to obtain informed consent, discuss the limitations of the methodology, obtain the parental decisions for return of incidental findings (II-2A) (recommendation 4) and provide post-test counselling for reporting of test results (III-A) (recommendation 9); (3) the resolution of chromosomal microarray analysis should be similar to postnatal microarray platforms to ensure small pathogenic variants are detected. To minimise the reporting of uncertain findings, it is recommended that variants of unknown significance (VOUS) smaller than 500 Kb deletion or 1 Mb duplication not be routinely reported in the prenatal context. Additionally, VOUS above these cut-offs should only be reported if there is significant supporting evidence that deletion or duplication of the region may be pathogenic (III-B) (recommendation 5); (4) secondary findings associated with a medically actionable disorder with childhood onset should be reported, whereas variants associated with adult-onset conditions should not be reported unless requested by the parents or disclosure can prevent serious harm to family members (III-A) (recommendation 8).

The working group recognises that there is variability across Canada in delivery of prenatal testing, and these recommendations were developed to promote consistency and provide a minimum standard for all provinces and territories across the country (recommendation 9).

Efficient and cost-effective genetic analysis of products of conception and fetal tissues using a QF-PCR/array CGH strategy; five years of data

BACKGROUND

Traditional testing of miscarriage products involved culture of tissue followed by G-banded chromosome analysis; this approach has a high failure rate, is labour intensive and has a resolution of around 10 Mb. G-banded chromosome analysis has been replaced by molecular techniques in some laboratories; we previously introduced a QF-PCR/MLPA testing strategy in 2007. To improve diagnostic yield and efficiency we have now updated our testing strategy to a more comprehensive QF-PCR assay followed by array CGH. Here we describe the results from the last 5 years of service.

METHODS

Fetal tissue samples and products of conception were tested using QF-PCR which will detect aneuploidy for chromosomes 13, 14, 15, 16, 18, 21, 22, X and Y. Samples that were normal were then tested by aCGH and all imbalance >1Mb and fully penetrant clinically significant imbalance <1Mb was reported.

RESULTS

QF-PCR analysis identified aneuploidy/triploidy in 25.6% of samples. aCGH analysis detected imbalance in a further 9.6% of samples; this included 1.8% with submicroscopic imbalance and 0.5% of uncertain clinical significance. This approach has a failure rate of 1.4%, compared to 30% for G-banded chromosome analysis.

CONCLUSIONS

This efficient QF-PCR/aCGH strategy has a lower failure rate and higher diagnostic yield than karyotype or MLPA strategies; both findings are welcome developments for couples with recurrent miscarriage.