Novel perspectives in fetal biomarker implementation for the noninvasive prenatal testing

Focus on the frontier issue: progress in noninvasive prenatal screening for fetal trisomy from clinical perspectives

The discovery of cell-free fetal DNA (cffDNA) in maternal blood and the rapid development of massively parallel sequencing have revolutionized prenatal testing from invasive to noninvasive. Noninvasive prenatal screening (NIPS) based on cffDNA enables the detection of fetal trisomy through sequencing, comparison, and bioassays. Its accuracy is better than that of traditional screening methods, and it is the most advanced clinical application of high-throughput sequencing technologies. However, the existing sequencing methods are limited by high costs and complex sequencing procedures. These limitations restrict the availability of NIPS for pregnant women. Many amplification methods have been developed to overcome the limitations of sequencing methods. The rapid development of non-sequencing methods has not been accompanied by reviews to summarize them. In this review, we initially describe the detection principles for sequencing-based NIPS. We summarize the rapidly evolving amplification technologies, focusing on the need to reduce costs and simplify the procedures. To ensure that the testing systems are feasible and that the testing processes are reliable, we expand our vision to the clinic. We evaluate the clinical validity of NIPS in terms of sensitivity, specificity, and positive predictive value. Finally, we summarize the application guidelines and discuss the corresponding quality control methods for NIPS. In addition to cffDNA, extracellular vesicle DNA, RNA, protein/peptide, and fetal cells can also be detected as biomarkers of NIPS. With the development of prenatal testing, NIPS has become increasingly important. Notably, NIPS is a screening test instead of a diagnostic test. The testing methods and procedures used in the NIPS process require standardization.

Validity and Utility of Non-Invasive Prenatal Testing for Copy Number Variations and Microdeletions: A Systematic Review

Valid data on prenatal cell-free DNA-based screening tests for copy number variations and microdeletions are still insufficient. We aimed to compare different methodological approaches concerning the achieved diagnostic accuracy measurements and positive predictive values. For this systematic review, we searched the Scopus and PubMed databases and backward citations for studies published between 2013 and 4 February 2022 and included articles reporting the analytical and clinical performance of cfDNA screening tests for CNVs and microdeletions. Of the 1810 articles identified, 32 met the criteria. The reported sensitivity of the applied tests ranged from 20% to 100%, the specificity from 81.62% to 100%, and the PPV from 3% to 100% for cases with diagnostic or clinical follow-up information. No confirmatory analysis was available in the majority of cases with negative screening results, and, therefore, the NPVs could not be determined. NIPT for CNVs and microdeletions should be used with caution and any developments regarding new technologies should undergo strict evaluation before their implementation into clinical practice. Indications for testing should be in correlation with the application guidelines issued by international organizations in the field of prenatal diagnostics.

Non-invasive prenatal screening for foetal trisomy: An assessment of reliability and reporting

OBJECTIVE

Non-invasive prenatal screening (NIPS) has been introduced as a routine screening technique for aneuploidies in the clinic. To evaluate its reliability and reporting standardization, the National Center for Clinical Laboratories launched an external quality assessment (EQA) program based on highly simulated samples.

METHODS

Maternal and child paired cell lines were digested by enzymes to obtain DNA fragments for the analysis panel, which were composed of 5% T21, 5% T18, 10% T13, 10% euploid, and 20% T18 samples. The samples were validated and distributed to laboratories along with scenarios and questionnaires for analysis.

RESULTS

Out of 350 participating laboratories, 98.6% correctly identified all samples. The concurrence rates of laboratories for the 5% T21, 5% T18, 10% T13, 10% euploid, and 20% T18 samples were 98.9%, 99.7%, 99.7%, 100%, and 100%, respectively. Enrichment increased the foetal fraction (FF) values by 2 ∼ 3-fold, but the z scores generated by the enrichment group fluctuated greatly. Other FF estimation techniques, such as the size-based and FF-QuantSC methods, generated slightly different FF values from the chr Y-based method. Furthermore, some laboratories omitted the suggestions of results in reports.

CONCLUSIONS

The participating laboratories provided highly reliable results for samples with relatively higher FF values. However, the absence of performance validation, laboratory errors, and low FF values were potential reasons for false-negative results. In addition, enrichment operations should be validated and normalized to guarantee NIPS reproducibility, plus further efforts are required to standardize the NIPS reports.

Noninvasive prenatal testing of α-thalassemia and β-thalassemia through population-based parental haplotyping

Background

Noninvasive prenatal testing (NIPT) of recessive monogenic diseases depends heavily on knowing the correct parental haplotypes. However, the currently used family-based haplotyping method requires pedigrees, and molecular haplotyping is highly challenging due to its high cost, long turnaround time, and complexity. Here, we proposed a new two-step approach, population-based haplotyping-NIPT (PBH-NIPT), using α-thalassemia and β-thalassemia as prototypes.

Methods

First, we deduced parental haplotypes with Beagle 4.0 with training on a large retrospective carrier screening dataset (4356 thalassemia carrier screening-positive cases). Second, we inferred fetal haplotypes using a parental haplotype-assisted hidden Markov model (HMM) and the Viterbi algorithm.

Results

With this approach, we enrolled 59 couples at risk of having a fetus with thalassemia and successfully inferred 94.1% (111/118) of fetal alleles. We confirmed these alleles by invasive prenatal diagnosis, with 99.1% (110/111) accuracy (95% CI, 95.1–100%).

Conclusions

These results demonstrate that PBH-NIPT is a sensitive, fast, and inexpensive strategy for NIPT of thalassemia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-021-00836-8.

Noninvasive prenatal diagnosis of hemophilia A by a haplotype-based approach using cell-free fetal DNA

Aim: We aimed to demonstrate noninvasive prenatal diagnosis (NIPD) of hemophilia A (HA) using a haplotype-based approach. Methods: Two families at risk for HA were recruited for this study. First, maternal haplotypes associated with pathogenic variants were constructed using the genotypes of the mothers and probands. Then, fetal haplotypes were deduced using a maternal haplotype-assisted hidden Markov model. Finally, the NIPD results were further confirmed by invasive prenatal diagnosis. Results: Two fetal genotypes were successfully inferred, with one normal fetus and one carrier fetus. The NIPD results were confirmed by invasive prenatal diagnosis, with a 100% consistency rate. Conclusion: Our test has been shown to be accurate and reliable. With further validation in a large patient cohort, this haplotype-based approach could be feasible for the NIPD of HA and other X-linked single-gene disorders.

Size profile of cell-free DNA: A beacon guiding the practice and innovation of clinical testing

Cell-free DNA (cfDNA) has pioneered the development of noninvasive prenatal testing and liquid biopsy, its emerging applications include organ transplantation, autoimmune diseases, and many other disorders; size profile of cfDNA is a crucial biological property and is essential for its clinical applications. Therefore, a thorough mastery of the characteristic and potential applications of cfDNA size profile is needed. Methods: Based on the recent researches, we summarized the size profile of cfDNA in pregnant women, tumor patients, transplant recipients and systemic lupus erythematosus (SLE) patients to explore the common features. We also concluded the applications of size profile in pre-analytical phases, analytical phases for novel assays, and preparation of quality control materials (QCMs). Results: The size profile of cfDNA shared common features in different populations, and was distributed as a "ladder" pattern with a dominant peak at ~166 bp. However, cfDNA entailed slightly discrepant characteristics due to specific tissues of origin. The dominant peaks of fetal and maternal cfDNA fragments in pregnant women were at 143 bp and 166 bp, respectively. The plasma cfDNA in tumor patients, transplant recipients, and SLE patients had a peak of around 166 bp. In pre-analytical phases, size profile served as a vital indicator to judge the eligibility of specimens, thus ensuring the successful implementation of assays. More importantly, the size profile had the potential to enrich short fragments, calculate fetal fraction, detect fetal abnormalities, predict tumor progress in analytical phase and to guide the preparation of QCMs. Conclusions: Our finding summarized the characteristics and potential applications of cfDNA size profile, providing clinical researchers with novel assays by the extensive application of cfDNA.