Screening of triploid with low-coverage whole-genome sequencing by a single-nucleotide polymorphism-based test in miscarriage tissue

Copy number variation sequencing for the products of conception: What is the optimal testing strategy

BACKGROUND

Copy number variation sequencing (CNV-seq) is crucial in prenatal diagnosis, but its limitations in detecting polyploidy, maternal cell contamination (MCC), and uniparental disomy (UPD) restrict its application in the analysis of products of conception (POCs). This study aimed to investigate an optimal genetic testing strategy for POCs in the era of CNV-seq.

METHODS

CNV-seq and quantitative fluorescent polymerase chain reaction (QF-PCR) were performed in all 4,211 spontaneous miscarriage cases. Different testing strategies were compared and the optimal testing strategies were proposed.

RESULTS

Of the 4,211 cases, 2561 (60.82%) exhibited clinically significant chromosomal abnormalities. CNV-seq alone, without QF-PCR, might misdiagnose 311 (7.39%) cases, including 278 polyploidy, 13 UPD, and 20 MCC. In 20 MCC cases identified by QF-PCR, CNV-seq successfully pinpointed the cause of miscarriage in 13 cases. Furthermore, in cases where QF-PCR suggested polyploidy, CNV-seq improved the diagnostic accuracy in 54 (1.28%) hypo/hypertriploidy cases. After comparing four different strategies, the sequential approach (initiating with CNV-seq followed by QF-PCR if necessary) emerged as advantageous, reducing approximately 70% of the cost associated with QF-PCR while maintaining result accuracy.

CONCLUSIONS

We propose an initial CNV-seq followed by QF-PCR if needed-an efficient and cost-effective strategy for the genetic analysis of POCs.

First preimplantation genetic testing case of Meckel syndrome with a novel homozygous TXNDC15 variant in a non-consanguineous Chinese family

BACKGROUND

Meckel-Gruber syndrome (MKS) is a perinatally lethal, genetically heterogeneous, autosomal recessive condition caused by defective primary cilium formation. So far, the association of TXNDC15-related MKS has been reported in only five independent families from diverse ethnic origins, including Saudi, Pakistani, Estonian, and Indian. Here, we report a fetus diagnosed with MKS at 12 weeks, exhibiting typical ultrasound findings.

METHODS

Low-coverage whole-genome sequencing was used to identify chromosomal abnormalities. Trio-base whole exome sequencing (trio-WES) was performed to investigate the potential pathogenic variants associated with MKS. Preimplantation genetic testing for monogenic disorders (PGT-M) was applied to prevent the transmission of the pathogenic variant.

RESULTS

A novel homozygous pathogenic variant in the TXNDC15 gene was identified through trio-WES. The application of PGT-M successfully prevented the transmission of the pathogenic variant and resulted in an ongoing pregnancy.

CONCLUSION

This is the first report of a TXNDC15 variant in the Chinese population and the first PGT case of TXNDC15-related MKS worldwide. The successful application of PGT-M in this family provides a potential approach for other monogenic diseases. Our case expands the variant spectrum of TXNDC15 and contributes to the molecular diagnosis and genetic counseling for MKS. This case underscores the importance of appropriate genetic testing methods and accurate genetic counseling in the diagnosis of rare monogenic diseases.

Validation and depth evaluation of low-pass genome sequencing in prenatal diagnosis using 387 amniotic fluid samples

BACKGROUND

Low-pass genome sequencing (LP GS) is an alternative to chromosomal microarray analysis (CMA). However, validations of LP GS as a prenatal diagnostic test for amniotic fluid are rare. Moreover, sequencing depth of LP GS in prenatal diagnosis has not been evaluated.

OBJECTIVE

The diagnostic performance of LP GS was compared with CMA using 375 amniotic fluid samples. Then, sequencing depth was evaluated by downsampling.

RESULTS

CMA and LP GS had the same diagnostic yield (8.3%, 31/375). LP GS showed all copy number variations (CNVs) detected by CMA and six additional variant of uncertain significance CNVs (>100 kb) in samples with negative CMA results; CNV size influenced LP GS detection sensitivity. CNV detection was greatly influenced by sequencing depth when the CNV size was small or the CNV was located in the azoospermia factor c (AZFc) region of the Y chromosome. Large CNVs were less affected by sequencing depth and more stably detected. There were 155 CNVs detected by LP GS with at least a 50% reciprocal overlap with CNVs detected by CMA. With 25 M uniquely aligned high-quality reads (UAHRs), the detection sensitivity for the 155 CNVs was 99.14%. LP GS using samples with 25 M UAHRs showed the same performance as LP GS using total UAHRs. Considering the detection sensitivity, cost and interpretation workload, 25 M UAHRs are optimal for detecting most aneuploidies and microdeletions/microduplications.

CONCLUSION

LP GS is a promising, robust alternative to CMA in clinical settings. A total of 25 M UAHRs are sufficient for detecting aneuploidies and most microdeletions/microduplications.

Application of Restriction Site-Associated DNA Sequencing (RAD-Seq) for Copy Number Variation and Triploidy Detection in Human

At present, low-pass whole-genome sequencing (WGS) is frequently used in clinical research and in the screening of copy number variations (CNVs). However, there are still some challenges in the detection of triploids. Restriction site-associated DNA sequencing (RAD-Seq) technology is a reduced-representation genome sequencing technology developed based on next-generation sequencing. Here, we verified whether RAD-Seq could be employed to detect CNVs and triploids. In this study, genomic DNA of 11 samples was extracted employing a routine method and used to build libraries. Five cell lines of known karyotypes and 6 triploid abortion tissue samples were included for RAD-Seq testing. The triploid samples were confirmed by STR analysis and also tested by low-pass WGS. The accuracy and efficiency of detecting CNVs and triploids by RAD-Seq were then assessed, compared with low-pass WGS. In our results, RAD-Seq detected 11 out of 11 (100%) chromosomal abnormalities, including 4 deletions and 1 aneuploidy in the purchased cell lines and all triploid samples. By contrast, these triploids were missed by low-pass WGS. Furthermore, RAD-Seq showed a higher resolution and more accurate allele frequency in the detection of triploids than low-pass WGS. Our study shows that, compared with low-pass WGS, RAD-Seq has relatively higher accuracy in CNV detection at a similar cost and is capable of identifying triploids. Therefore, the application of this technique in medical genetics has a significant potential value.

Next-Generation Sequencing Is More Efficient at Detecting Mosaic Embryos and Improving Pregnancy Outcomes than Single-Nucleotide Polymorphism Array Analysis

We compared chromosomal mosaicism, detected by next-generation sequencing (NGS), during preimplantation genetic testing (PGT) with that detected by single-nucleotide polymorphism (SNP) array-based PGT to assess the pregnancy outcomes associated with both platforms in a retrospective cohort study of patients undergoing in vitro fertilization in a single university-based assisted reproduction center. In total, 6427 blastocysts biopsied from 1513 patients who underwent 2833 oocyte retrievals from January 2017 to February 2019 were identified. The incidence of mosaicism was significantly higher in the NGS-based PGT group than in the SNP array-based PGT group. Furthermore, some aneuploid specimens were affected by mosaicism. The total mosaicism detection rate with NGS-based PGT (23.3%) was significantly higher than that with SNP array-based PGT (7.7%). Mosaicism rates were similar when stratified by maternal age or PGT type. The SNP array cohort showed a significantly higher spontaneous abortion rate than the NGS cohort (10.07% versus 6.33%; P = 0.0403). The ongoing pregnancy/live birth rate was higher in the NGS cohort (44.1%) than in the SNP array cohort (42.28%). Our results confirm that NGS-based PGT can detect mosaicism more frequently than SNP array-based PGT in trophectoderm specimens. Therefore, clinical application of NGS for PGT may improve pregnancy outcomes compared with that of SNP array-based PGT. More detailed blastocyst detection and classification is necessary to prioritize embryo transfers.