Targeted sequencing of maternal plasma for haplotype-based non-invasive prenatal testing of spinal muscular atrophy

First-trimester noninvasive prenatal diagnosis of seven facioscapulohumeral muscular dystrophy type 1 families using SNP-based amplicon sequencing: An earlier, rapid and safer way

The study is to explore the feasibility and value of SNP-based noninvasive prenatal diagnosis (NIPD) for facioscapulohumeral muscular dystrophy type 1 (FSHD1) in early pregnancy weeks. We prospectively collected seven FSHD1 families, with an average gestational age of 8+6. Among these seven couples, there were three affected FSHD1 mothers and four affected fathers. A multiplex-PCR panel comprising 402 amplicons was designed to selective enrich for highly heterozygous SNPs upstream of the DUX4 gene. Risk haplotype was constructed based on familial linkage analysis. Fetal genotypes were accurately inferred through relative haplotype dosage analysis using Bayes Factor. All tests were successfully completed in a single attempt, and no recombination events were detected. NIPD results were provided within a week, which is 4 weeks earlier than karyomapping and 7 weeks earlier than Bionano single-molecule optical mapping (BOM). Ultimately, five FSHD1 fetuses and two normal fetuses were successfully identified, with a 100% concordance rate with karyomapping and BOM. Therefore, SNP-based NIPD for FSHD1 was demonstrated to be feasible and accurate in early weeks of gestation, although the risk of recombination events cannot be completely eliminated. In the future, testing of more cases is still necessary to fully determine the clinical utility.

Exploring factors impacting haplotype-based noninvasive prenatal diagnosis for single-gene recessive disorders

Haplotype-based noninvasive prenatal diagnosis (NIPD) is applicable for various recessive single-gene disorders in proband families. However, a comprehensive exploration of critical factors influencing the assay performance, such as fetal fraction, informative single nucleotide polymorphism (SNP) count, and recombination events, has yet to be performed. It is critical to identify key factors affecting NIPD performance, including its accuracy and success rate, and their impact on clinical diagnostics to guide clinical practice. We conducted a prospective study, recruiting 219 proband families with singleton pregnancies at risk for eight recessive single-gene disorders (Duchenne muscular dystrophy, spinal muscular atrophy, phenylketonuria, methylmalonic acidemia, hemophilia A, hemophilia B, non-syndromic hearing loss, and congenital adrenal hyperplasia) at 7-14 weeks of gestation. Haplotype-based NIPD was performed by evaluating the relative haplotype dosage (RHDO) in maternal circulation, and the results were validated via invasive prenatal diagnosis or newborn follow-ups. Among the 219 families, the median gestational age at first blood draw was 8+5 weeks. Initial testing succeeded for 190 families and failed for 29 due to low fetal fraction (16), insufficient informative SNPs (9), and homologous recombination near pathogenic variation (4). Among low fetal fraction families, successful testing was achieved for 11 cases after a redraw, while 5 remained inconclusive. Test failures linked to insufficient informative SNPs correlated with linkage disequilibrium near the genes, with F8 and MMUT exhibiting the highest associated failure rates (14.3% and 25%, respectively). Homologous recombination was relatively frequent around the DMD and SMN1 genes (8.8% and 4.8%, respectively) but led to detection failure in only 44.4% (4/9) of such cases. All NIPD results from the 201 successful families were consistent with invasive diagnostic findings or newborn follow-up. Fetal fraction, informative SNPs count, and homologous recombination are pivotal to NIPD performance. Redrawing blood effectively improves the success rate for low fetal fraction samples. However, informative SNPs count and homologous recombination rates vary significantly across genes, necessitating careful consideration in clinical practice. We have designed an in silico method based on linkage disequilibrium data to predict the number of informative SNPs. This can identify genomic regions where there might be an insufficient number of SNPs, thereby guiding panel design. With these factors properly accounted for, NIPD is highly accurate and reliable.

Current Advances in Genetic Testing for Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is one of the most common genetic disorders worldwide, and genetic testing plays a key role in its diagnosis and prevention. The last decade has seen a continuous flow of new methods for SMA genetic testing that, along with traditional approaches, have affected clinical practice patterns to some degree. Targeting different application scenarios and selecting the appropriate technique for genetic testing have become priorities for optimizing the clinical pathway for SMA. In this review, we summarize the latest technological innovations in genetic testing for SMA, including MassArray®, digital PCR (dPCR), next-generation sequencing (NGS), and third-generation sequencing (TGS). Implementation recommendations for rationally choosing different technical strategies in the tertiary prevention of SMA are also explored.

A novel method for noninvasive diagnosis of monogenic diseases from circulating fetal cells

OBJECTIVE

To establish a method for noninvasive fetal cell isolation from maternal blood and prenatal testing of monogenic diseases by a combination of direct sequencing and targeted NGS-based SNP haplotyping from single fetal cells.

METHOD

Peripheral blood of pregnant women in two families (congenital deafness and ichthyosis) was collected. After density-based separation and immunostaining with multiple biomarkers, candidate fetal cells were identified by high-throughput imagine analysis and picked up by automation. Individual fetal cells were subjected to STR-genotyping to identify their origin. Pathogenic mutations were identified by direct Sanger sequencing, and a combination of targeted NGS and SNP haplotyping using a custom panel. All the results were compared with amniotic fluid DNA.

RESULTS

Fetal trophoblasts were successfully harvested from maternal blood. STR-genotyping confirmed the fetal origin. Direct sequencing of pathogenic genetic mutations in fetal cells showed consistent results with amniotic fluid samples. For congenital deafness family, NGS-based SNP haplotyping also correctly identified the fetal haplotype. This single cell haplotyping method can be used to diagnose various genetic diseases.

CONCLUSION

We have established a method for noninvasive prenatal testing of monogenic diseases from circulating trophoblast cells. This cell-based NIPT can be further applied to the prenatal diagnosis of various monogenic diseases.

Noninvasive prenatal diagnosis of cobalamin C (cblC) deficiency through target region sequencing of cell-free DNA in maternal plasma

OBJECTIVE

This study aimed to validate the feasibility of haplotype-based noninvasive prenatal diagnosis (NIPD) of cobalamin C (cblC) deficiency.

METHOD

This method includes three steps: First, targeted sequencing was performed on 21 families affected by cblC deficiency (including the couples and probands). Second, parental haplotypes linked with the pathogenic variant were determined using the genotypes of trios. Then, the fetal haplotypes were inferred through a parental haplotype assisted hidden Markov model (HMM). The NIPD results were confirmed by using the invasive procedures.

RESULTS

Twenty-one fetal genotypes were successfully inferred by NIPD including three compound heterozygotes with cblC deficiency, nine heterozygote carriers of cblC deficiency, and nine normal fetuses. The NIPD results were confirmed using the invasive procedures with 100% concordant rate.

CONCLUSION

This result has shown that haplotype-based NIPD of cblC deficiency has high concordant rate and indicated potential clinical utility as a pregnancy diagnosis method for high-risk carrier couples.

Development and validation of a haplotype-free technique for non-invasive prenatal diagnosis of spinal muscular atrophy

OBJECTIVE

To develop a technique for non-invasive prenatal diagnosis of spinal muscular atrophy and validate its performance.

STUDY DESIGN

Pregnant women with 1 copy of SMN1 and male fetuses were enrolled. Seventeen women were included in test set A, and 10 of them were selected into test set B randomly and blinded. The two sets were tested independently by two different researchers blinded to fetal genotypes. Fetal DNA fractions were calculated based on the relative proportion of mapped chromosome Y sequencing reads. An algorithm was developed to decide fetal SMN1 copy numbers.

RESULTS

The concordance rate with the results of MLPA testing of amniocyte DNA was 94.12% in test set A and 90% in set B. For all tests with a classifiable result, the percent of agreement with the results of MLPA testing of amniocyte DNA was up to 100% (25/25).

CONCLUSION

We have developed a direct, rapid, and low-cost technique, which has a potential to be utilized for first-trimester non-invasive prenatal diagnosis and screening for spinal muscular atrophy with considerable reliability and feasibility.

Novel perspectives in fetal biomarker implementation for the noninvasive prenatal testing

Noninvasive prenatal testing (NIPT) utilizes cell-free fetal DNA (cffDNA) present in maternal peripheral blood to detect chromosomal abnormalities. The detection of 21-trisomy, 18-trisomy, and 13-trisomy in the fetus has become a common screening method during pregnancy and has been widely applied in routine clinical testing because of its analytical and clinical validity. Currently, noninvasive prenatal testing involving copy number variations (CNVs) and other frequent single-gene disorders is being widely studied, and it plays an important and indispensable role in prenatal detection. The multiple approaches that have been reported and validated by various laboratories have different merits and limitations. Their clinical validity, utility, and application vary with different diseases. This review summarizes the principles, methods, advantages, and limitations of noninvasive prenatal testing for the detection of aneuploidy, CNVs and single-gene disorders. Before implementation of NIPT into clinical practice, a list of criteria that the application must meet is crucial. Essential parameters such as clinical sensitivity, clinical specificity, positive predictive value (PPV) and negative predictive value (NPV) are required to properly evaluate the clinical validity and utility of NIPT. We then discuss and analyze these clinical parameters and clinical application guidelines, providing physicians and scientists with feasible strategies and the latest research information.

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.

Haplotype-Based noninvasive prenatal diagnosis for duchenne muscular dystrophy: A pilot study in South China

OBJECTIVE

To explore the accuracy and feasibility of noninvasive prenatal diagnosis (NIPD) for Duchenne Muscular Dystrophy (DMD) based on the haplotype approach.

METHODS

We recruited singleton pregnancies at-risk of DMD at 12-25 weeks of gestation from 17 families who all had a proband child affected by DMD. We have identified the pathogenic mutations in probands and their mothers by multiplex ligation-dependent probe amplification (MLPA). To construct parental haplotypes, we performed captured sequencing on genomic DNA from parents and probands. The integration analysis of parental haplotypes and targeted sequencing results of maternal plasma DNA were used to infer the fetal haplotype and genotypes in the DMD gene. Fetal DMD genotypes were further confirmed by invasive prenatal diagnosis.

RESULT

We have successfully performed the haplotype-based NIPD in all recruited families. Ten fetuses were identified as normal, including four female and six male fetuses. Four female fetuses were carriers, and the other three male fetuses were affected by DMD with exons 49-52 deletion, exons 8-37 deletion and c.628 G > T mutation, respectively. The results of NIPD were consistent with those of invasive diagnosis.

CONCLUSION

Haplotype-based NIPD for DMD by targeted sequencing is promising and has the potential for clinical application.

Prenatal aspects in spinal muscular atrophy: From early detection to early presymptomatic intervention

With the recent advances in spinal muscular atrophy therapies, the complete scenario of standard of care and following up is changing not only in the clinical field with new phenotypes emerging but also with new expectations for patients, caregivers and health providers. The actual evidence indicates that early intervention and treatment is crucial for better response and prognosis. Knowledge of the prenatal and pre-symptomatic postnatal stages of the disease are becoming essential to consider the opportunities of timely diagnosis and to decide the earliest therapeutic intervention.

Next generation sequencing: Coping with rare genetic diseases in China

With a population of 1.4 billion, China shares the largest burden of rare genetic diseases worldwide. Current estimates suggest that there are over ten million individuals afflicted with chromosome disease syndromes and well over one million individuals with monogenic disease. Care of patients with rare genetic diseases remains a largely unmet need due to the paucity of available and affordable treatments. Over recent years, there is increasing recognition of the need for affirmative action by government, health providers, clinicians and patients. The advent of new next generation sequencing (NGS) technologies such as whole genome/exome sequencing, offers an unprecedented opportunity to provide large-scale population screening of the Chinese population to identify the molecular causes of rare genetic diseases. As a surrogate for lack of effective treatments, recent development and implementation of noninvasive prenatal testing (NIPT) in China has the greatest potential, as a single technology, for reducing the number of children born with rare genetic diseases.