Sensitive Monogenic Noninvasive Prenatal Diagnosis by Targeted Haplotyping

A Cell-free DNA Barcode-Enabled Single-Molecule Test for Noninvasive Prenatal Diagnosis of Monogenic Disorders: Application to β-Thalassemia

Noninvasive prenatal testing of common aneuploidies has become routine over the past decade, but testing of monogenic disorders remains a challenge in clinical implementation. Most recent studies have inherent limitations, such as complicated procedures, a lack of versatility, and the need for prior knowledge of parental genotypes or haplotypes. To overcome these limitations, a robust and versatile next-generation sequencing-based cell-free DNA (cfDNA) allelic molecule counting system termed cfDNA barcode-enabled single-molecule test (cfBEST) is developed for the noninvasive prenatal diagnosis (NIPD) of monogenic disorders. The accuracy of cfBEST is found to be comparable to that of droplet digital polymerase chain reaction (ddPCR) in detecting low-abundance mutations in cfDNA. The analytical validity of cfBEST is evidenced by a β-thalassemia assay, in which a blind validation study of 143 at-risk pregnancies reveals a sensitivity of 99.19% and a specificity of 99.92% on allele detection. Because the validated cfBEST method can be used to detect maternal-fetal genotype combinations in cfDNA precisely and quantitatively, it holds the potential for the NIPD of human monogenic disorders.

Recent trends in prenatal genetic screening and testing

Prenatal testing in recent years has been moving toward non-invasive methods to determine the fetal risk for genetic disorders without incurring the risk of miscarriage. Rapid progress of modern high-throughput molecular technologies along with the discovery of cell-free fetal DNA in maternal plasma led to novel screening methods for fetal chromosomal aneuploidies. Such tests are referred to as non-invasive prenatal tests (NIPTs), non-invasive prenatal screening, or prenatal cell-free DNA screening. Owing to many advantages, the adoption of NIPT in routine clinical practice was very rapid and global. As an example, NIPT has recently become a standard screening procedure for all pregnant women in the Netherlands. On the other hand, invasive sampling procedures remain important, especially for their diagnostic value in the confirmation of NIPT-positive findings and the detection of Mendelian disorders. In this review, we focus on current trends in the field of NIPT and discuss their benefits, drawbacks, and consequences in regard to routine diagnostics.

Validation of Extensive Next-Generation Sequencing Method for Monogenic Disorder Analysis on Cell-Free Fetal DNA: Noninvasive Prenatal Diagnosis

During pregnancy, a percentage of the cell-free DNA circulating in the maternal blood is represented by the cell-free fetal DNA (cffDNA), constituting an accessible source for noninvasive prenatal genetic screening. The coexistence of the maternal DNA, the dominant fraction of cell-free DNA, together with the cffDNA component and the scarcity of the cffDNA itself make applying traditional methods of genetics and molecular biology impossible. Next-generation sequencing methods are widely used to study fetal aneuploidies. However, in monogenic disorders, there have been relatively few studies that analyzed single mutations. We present a method for the analysis of an extended group of gene variants associated with recessive and dominant autosomal disorders using next-generation sequencing. The proposed test should allow a complete analysis of common genetic disorders and pathogen-associated variants for diagnostic use. The analysis of cffDNA for single gene disorders may replace invasive prenatal diagnosis methods, associated with the risk of spontaneous abortion and psychological stress for patients. The proposed test should assess reproductive risk for both genetic family disorders and de novo occurrences of the disease. The application of this method to a case of beta-thalassemia is also discussed.

A Reappraisal of Circulating Fetal Cell Noninvasive Prenatal Testing

New tools for higher-resolution fetal genome analysis including microarray and next-generation sequencing have revolutionized prenatal screening. This article provides commentary on this rapidly advancing field and a future perspective emphasizing circulating fetal cell (CFC) utility. Despite the tremendous technological challenges associated with their reliable and cost-effective isolation from maternal blood, CFCs have a strong potential to bridge the gap between the diagnostic sensitivity of invasive procedures and the desirable noninvasive nature of cell-free fetal DNA (cffDNA). Considering the rapid advances in both rare cell isolation and low-input DNA analysis, we argue here that CFC-based noninvasive prenatal testing is poised to be implemented clinically in the near future.

Development of a common platform for the noninvasive prenatal diagnosis of X-linked diseases

OBJECTIVE

The aim of this study was to develop a common targeted massively parallel sequencing platform for the noninvasive prenatal diagnosis (NIPD) of multiple X-linked diseases.

METHOD

The custom capture probe was designed to target 33 genes and recombination hotspots. We tested the carrier mother and male proband pair of 6 families. Plasma DNA of the pregnant carrier mother was collected at different gestational weeks and sequenced. The fetal genotype of each family was determined by estimating the imbalance between the 2 maternal haplotypes constructed using a common custom-designed platform.

RESULTS

The targeted sequencing of the maternal, proband, and fetal genomic DNAs and maternal plasma DNAs resulted in uniform coverage across the target region. Three to 5 recombination points were observed in each sample. However, these recombination points did not affect the haplotype dosage analysis for fetal genotype prediction. Consequently, all fetal genotypes in the 6 families obtained from haplotype dosage analysis of maternal plasma sequencing data were predicted correctly.

CONCLUSIONS

Since a single platform that covers multiple diseases may prevent the need for disease-specific probes for the NIPD of individual disorders, this approach may provide a practical advantage for clinically implementing the NIPD of X-linked diseases.

Introducing new and emerging genetic tests into prenatal care

Given the rapid advances in genomics, translating new genomic tests effectively into prenatal clinical practice remains challenging. We discuss emerging genetic tests, considerations for their use, how tests should ideally be validated prior to use in clinical practice, and the role of the Federal Drug Administration, Clinical Laboratory Improvement Amendments (CLIA) laboratories, commercial laboratories, insurers, and professional societies such as the American College of Obstetricians and Gynecologists (ACOG), and the Society for Maternal-Fetal Medicine (SMFM) in the introduction of new prenatal genetic tests. After the introduction of new tests into the prenatal clinic, it is critical to utilize shared databases with measured outcomes to improve clinical care as well as to advance science.

Fast Temperature-Gradient COLD PCR for the enrichment of the paternally inherited SNPs in cell free fetal DNA; an application to non-invasive prenatal diagnosis of β-thalassaemia

Objective

To develop a sensitive, specific, simple, cost-effective and reproducible platform for the non-invasive prenatal detection of paternally inherited alleles for β-thalassaemia. The development of such an assay is of major significance in order to replace currently-applied invasive methods containing inherent fetal loss risks.

Methods

We present a fast Temperature-Gradient Co-amplification at Lower Denaturation Temperature Polymerase Chain Reaction (fast TG COLD PCR) methodology for the detection of the paternally-inherited fetal alleles in maternal plasma. Two single-nucleotide polymorphisms (SNPs), rs7480526 (G/T) and rs968857 (G/A) that are located on the β-globin gene cluster and exhibit a high degree of heterozygosity in the Cypriot population were selected for evaluation. Seventeen maternal plasma samples from pregnancies at risk for β-thalassemia were analysed for the selected SNPs using the novel fast TG COLD PCR assay.

Results

Using fast TG COLD PCR, the paternally inherited allele in cell free fetal DNA was correctly determined for all the 17 maternal plasma samples tested, showing full agreement with the Chorionic Villus Sampling (CVS) analysis.

Conclusions

Our findings are encouraging and demonstrate the efficiency and sensitivity of fast TG COLD PCR in detecting the minor paternally-inherited fetal alleles in maternal plasma for the development of a NIPD assay for β-thalassaemia.

Targeted linked-read sequencing for direct haplotype phasing of maternal DMD alleles: a practical and reliable method for noninvasive prenatal diagnosis

For the noninvasive prenatal diagnosis (NIPD) of X-linked recessive diseases such as Duchenne muscular dystrophy (DMD), maternal haplotype phasing is a critical step for dosage analysis of the inherited allele. Until recently, the proband-based indirect haplotyping method has been preferred despite its limitations for use in clinical practice. Here, we describe a method for directly determining the maternal haplotype without requiring the proband’s DNA in DMD families. We used targeted linked-read deep sequencing (mean coverage of 692×) of gDNA from 5 mothers to resolve their haplotypes and predict the mutation status of the fetus. The haplotype of DMD alleles in the carrier mother was successfully phased through a targeted linked-read sequencing platform. Compared with the proband-based phasing method, linked-read sequencing was more accurate in differentiating whether the recombination events occurred in the proband or in the fetus. The predicted inheritance of the DMD mutation was diagnosed correctly in all 5 families in which the mutation had been confirmed using amniocentesis or chorionic villus sampling. Direct haplotyping by this targeted linked-read sequencing method could be used as a phasing method for the NIPD of DMD, especially when the genomic DNA of the proband is unavailable.

Update on diagnosis and management of congenital adrenal hyperplasia due to 21-hydroxylase deficiency

PURPOSE OF REVIEW

Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is a relatively common inherited disorder of cortisol biosynthesis that can be fatal if untreated.

RECENT FINDINGS

The basic biochemistry and genetics of CAH have been known for decades but continue to be refined by the discoveries of an alternative 'backdoor' metabolic pathway for adrenal androgen synthesis and the secretion of 11-hydroxy and 11-keto analogs of known androgens, by the elucidation of hundreds of new mutations, and by the application of high-throughput sequencing techniques to noninvasive prenatal diagnosis. Although hydrocortisone is a mainstay of treatment, overtreatment may have adverse effects on growth, risk of obesity, and cardiovascular disease; conversely, undertreatment may increase risk of testicular adrenal rest tumors in affected men.

SUMMARY

Refinements to screening techniques may improve the positive predictive value of newborn screening programs. Alternative dosing forms of hydrocortisone and additional therapeutic modalities are under study. Although surgical treatment of virilized female genitalia is widely accepted by families and patients, it is not without complications or controversy, and some families choose to defer it.

cfDNA screening and diagnosis of monogenic disorders - where are we heading?

Cell‐free fetal DNA analysis for non‐invasive prenatal screening of fetal chromosomal aneuploidy has been widely adopted for clinical use. Fetal monogenic diseases have also been shown to be amenable to non‐invasive detection by maternal plasma DNA analysis. A number of recent technological developments in this area has increased the level of clinical interest, particularly as one approach does not require customized reagents per mutation. The mutational status of the fetus can be assessed by determining which parental haplotype that fetus has inherited based on the detection of haplotype‐associated SNP alleles in maternal plasma. Such relative haplotype dosage analysis requires the input of the parental haplotype information for interpretation of the fetal inheritance pattern from the maternal plasma DNA data. The parental haplotype information can be obtained by direct means, reducing the need to infer haplotypes using DNA from other family members. The technique also allows the assessment of complex mutations and has multiplexing capabilities where a number of genes and mutations can be assessed at the same time. These advantages allow non‐invasive prenatal diagnosis of fetal monogenic diseases to be much more scalable. These applications may drive the next wave of clinical adoption of cell‐free fetal DNA testing. © 2018 The Authors Prenatal Diagnosis Published by John Wiley & Sons Ltd

What's already known about this topic?

NIPD for some monogenic diseases is now in clinical service.

Current NIPD is based on bespoke mutation‐specific assays, or haplotype inference which requires proband DNA.

What does this study add?

The application of universal haplotype‐based NIPD can be extended to most pregnancies at risk for monogenic diseases.

The universal protocol circumvents the need for bespoke assays or access to proband DNA.