The Evolving Role of Next-Generation Sequencing in Screening and Diagnosis of Hemoglobinopathies

The Application of Clinical and Molecular Diagnostic Techniques to Identify a Rare Haemoglobin Variant

Haemoglobin disorders represent a heterogeneous group of inherited conditions that involve at least one genetic abnormality in one or more of the globin chains, resulting in changes in the structure, function, and/or amount of haemoglobin molecules, which are very important for their related clinical aspects. Detecting and characterizing these disorders depends primarily on laboratory methods that employ traditional approaches and, when necessary, newer methodologies essential for solving a number of diagnostic challenges. This review provides an overview of key laboratory techniques in the diagnosis of haemoglobinopathies, focusing on the challenges, advancements, and future directions in this field. Moreover, many haemoglobinopathies are benign and clinically silent, but it is not uncommon to find unexpected variants during routine laboratory tests. The present work reported a rare and clinically interesting case of identification of haemoglobin fractions in an adult man by the determination of glycated haemoglobin (HbA1c) during a routine laboratory assessment, highlighting how the correct use of laboratory data can modify and improve the patient's clinical management.

Thalassemia screening by third-generation sequencing: Pilot study in a Thai population

Background

Conventional thalassemia screening takes a stepwise approach and has limitations in comprehensively identifying all spectrums of mutations. This study aimed to investigate the performance of third-generation sequencing (TGS) compared to conventional molecular testing.

Methods

TGS was applied to validate all known variants detected by conventional testing and to detect missing variants in undiagnosed cases. The study was conducted at Maharaj Nakorn Chiang Mai Hospital between December 2021 and April 2022.

Results

In total, 19 cases were included in this study, among which 52.6% (10/19) had known thalassemia variants, while 47.7% (9/19) cases were undiagnosed by conventional methods. All 16 variants previously detected were validated by TGS, and TGS additionally detected 43.8% (7/16) thalassemia variants for 36.8% (7/19) cases.

Conclusion

TGS could provide additional genetic diagnoses compared with conventional methods. Further cost-effectiveness studies with a larger sample size are needed to explore the role of TGS in clinical practices.

Third-generation sequencing identified a novel complex variant in a patient with rare alpha-thalassemia

BACKGROUND

Thalassemias represent some of the most common monogenic diseases worldwide and are caused by variations in human hemoglobin genes which disrupt the balance of synthesis between the alpha and beta globin chains. Thalassemia gene detection technology is the gold standard to achieve accurate detection of thalassemia, but in clinical practice, most of the tests are only for common genotypes, which can easily lead to missing or misdiagnosis of rare thalassemia genotypes.

CASE PRESENTATION

We present the case of an 18-year-old Chinese female with abnormal values of routine hematological indices who was admitted for genetic screening for thalassemia. Genomic DNA was extracted and used for the genetic assays. Gap polymerase chain reaction and agarose gel electrophoresis were performed to detect HBA gene deletions, while PCR-reverse dot blot hybridization was used to detect point mutations in the HBA and HBB genes. Next-generation sequencing and third-generation sequencing (TGS) were used to identify known and potentially novel genotypes of thalassemia. We identified a novel complex variant αHb WestmeadαHb Westmeadαanti3.7/-α3.7 in a patient with rare alpha-thalassemia.

CONCLUSIONS

Our study identified a novel complex variant that expands the thalassemia gene variants spectrum. Meanwhile, the study suggests that TGS could effectively improve the specificity of thalassemia gene detection, and has promising potential for the discovery of novel thalassemia genotypes, which could also improve the accuracy of genetic counseling. Couples who are thalassemia carriers have the opportunity to reduce their risk of having a child with thalassemia.

Detection of 13 Novel Variants and Investigation of Mutation Distribution by Next Generation Sequencing in Hemoglobinopathies: A Single Center Experience

Hemoglobinopathies are the most common monogenic disorders in the world. Traditional diagnostic algorithms generated by conventional methods for thalassemia can be labor-intensive and time-consuming due to the complexities of the genes involved and the variability in disease-causing mutations. With the advantages of next-generation sequencing (NGS) technology, molecular analysis of highly complex diseases such as hemoglobinopathies has become easier. Next-generation sequencing is a highly sensitive and effective method due to its capacity to sequence many gene regions simultaneously while allowing good read depths. In this study, single nucleotide changes, small deletions and copy number variations in HBA1, HBA2 and HBB in 914 patients with suspected hemoglobinopathy were analysed with NGS. At least one HBA1, HBA2, HBB or HBD variant was detected in 483 (52.8%) patients. Ten novel variants were detected in HBA1 and HBA2, three in HBB, and one in HBD. From these variants, c.*76T > A, c.301-24 G > A, c.301-24G > C c.-41C > G, c.-37-40C > G, c.-9G > C, c. 95 + 9C > T, c.95 + 26C > A, c.95 + 38C > T and c.*18C > G variants were located in α-globin genes, c.-25T > C, c.*103T > C and c92 + 39A > G variants were located in β-globin genes, and c.-43C > A was located in HBD. This is the first comprehensive study using NGS for the molecular diagnosis of hemoglobinopathies in Turkey. Accurate molecular diagnosis is of critical importance in hemoglobinopathies which are a public health problem due to their increased prevalence, high burden to society, and lack of curative treatment. Currently, NGS appears to be an advanced option over conventional methods to detect all variants occurring by molecular mechanisms and simultaneously analyse many genomic sequences.

Severe Transfusion-Dependent Thalassemia in Compound Heterozygote Palestinian Siblings with Two α-Globin Gene Defects, Hb Taybe D HBA1: C.119_121delCCA Mutation and HBA2: C.*94A > G Mutation

Alpha and Beta Thalassemia are autosomal recessive anemias that cause significant morbidity and mortality worldwide, especially in the Middle East and North Africa (MENA) region where carrier rates reach up to 50%. We report the case of two siblings of Palestinian origin born who presented to our tertiary healthcare center for the management of severe transfusion dependent hemolytic anemia. Before presentation to our center, the siblings were screened for a-thalassemia using the Alpha-globin StripAssay. They were found to carry the α2 polyA-1 [AATAAA > AATAAG] mutation in the heterozygous form, which was insufficient to make a diagnosis. No pathogenic variants were detected on Sanger sequencing of the HBB gene. Full sequencing of the a-gene revealed compound heterozygous variants (HBA1:c.119_121delCCA and the previously detected HBA2:c.*+94A > G Poly A [A->G]) with trans inheritance. This report highlights the impact of non-deletional mutations on α-globin chain stability. The compound heterozygosity of a rare α-globin chain pathogenic variant with a polyadenylation mutation in the probands leads to clinically severe a-thalassemia. Due to the high carrier status, the identification of rare mutations through routine screening techniques in our populations may be insufficient. Ongoing collaboration among hematologists, medical geneticists, and counselors is crucial for phenotypic-genotypic correlation and assessment of adequate genetic testing schemes.

Identification of a novel 91.5 kb-deletion (αα)FJ in the α-globin gene cluster using single-molecule real-time (SMRT) sequencing

OBJECTIVES

To present a novel 91.5-kb deletion of the α-globin gene cluster (αα)FJ identified by genetic assay and prenatal diagnosis in a Chinese family.

SUBJECTS AND METHODS

The proband was a 34-year-old G3P1 (Gravida 3, Para 1) female at the gestational age of 21+ weeks with a history of an edematous fetus. A routine genetic assay (reverse dot blot hybridization, RDB) was performed to detect common thalassemia mutations. Multiplex ligation-dependent probe amplification (MLPA) and single-molecule real-time technology (SMRT) were used to detect rare thalassemia mutations.

RESULTS

The hematological phenotypes of the proband, her mother, elder sister, husband, daughter, and nephew were consistent with the phenotype of α-thalassemia trait. No mutations were found in these family members by RDB, except for the proband's husband who carried an α-globin gene deletion --SEA/αα. MLPA results showed that the proband and other α-thalassemia-suspected relatives had heterozygous deletions around the POLR3K-3-463nt, HS40-178nt, and HBA-HS40-382nt probes. The 5'-breakpoint was out of probe scope and could not be determined. SMRT was performed and a 91.5-kb deletion (NC_000016.10: g.39268_130758del) in the α-globin gene cluster (αα)FJ was identified in the proband and other suspected relatives, which could explain their phenotypes. At the proband's gestational age of 22+ weeks, an amniotic fluid sample was collected and analyzed. As only the 91.5-kb deletion (αα)FJ was identified in the fetus with RDB, MLPA, and SMRT. The proband was suggested to continue the pregnancy.

CONCLUSION

We first reported a 91.5-kb deletion (NC_000016.10: g.hg38-chr16:39268-_130758del) of the HS-40 region in the α-globin gene cluster (αα)FJ identified in a Chinese family. Since the HS-40 loss of heterozygosity in combination with the heterozygous deletion --SEA might result in Hb Bart's hydrops fetalis, routine genetic assay, and SMRT were recommended to individuals at risk for prenatal diagnosis.

β-Thalassemia Trait Caused by SUPT5H Defects: Another Case Report

We identified a novel mutation in the SUPT5H gene in a Chinese female who presented with a β-thalassemia trait. The substitution of c.193C > T (p.Arg65*) leads to a premature stop codon on residue 65 and could be associated with haploinsufficiency. This variant was inherited from the mother who also had the asymptomatic phenotype of β-thalassemia trait. Our case further supports the role of SUPT5H as a potential β-globin chain production-modulating gene.

Application of Targeted Next-Generation Sequencing for the Investigation of Thalassemia in a Developing Country: A Single Center Experience

Thalassemia is identified as a prevalent disease in Malaysia, known to be one of the developing countries. Fourteen patients with confirmed cases of thalassemia were recruited from the Hematology Laboratory. The molecular genotypes of these patients were tested using the multiplex-ARMS and GAP-PCR methods. The samples were repeatedly investigated using the Devyser Thalassemia kit (Devyser, Sweden), a targeted NGS panel targeting the coding regions of hemoglobin genes, namely the HBA1, HBA2, and HBB genes, which were used in this study. There were many different genetic variants found in 14 unrelated cases. Out of all fourteen cases, NGS was able to determine an additional -50 G>A (HBB:c.-100G>A) that were not identified by the multiplex-ARMS method, including HBA2 mutations, namely CD 79 (HBA2:c.239C>G). Other than that, CD 142 (HBA2:c.427T>C) and another non-deletional alpha thalassemia and alpha triplication were also not picked up by the GAP-PCR methods. We illustrated a broad, targeted NGS-based test that proposes benefits rather than using traditional screening or basic molecular methods. The results of this study should be heeded, as this is the first report on the practicality of targeted NGS concerning the biological and phenotypic features of thalassemia, especially in a developing population. Discovering rare pathogenic thalassemia variants and additional secondary modifiers may facilitate precise diagnosis and better disease prevention.

Predicting thalassemia using deep neural network based on red blood cell indices

BACKGROUND AND OBJECTIVE

The traditional statistical screening method for thalassemia based on red blood cell (RBC) indices is being replaced by machine learning. Here, we developed deep neural networks (DNNs) that outperformed the traditional method for predicting thalassemia.

METHOD

Using a dataset of 8693 records comprising genetic tests and other 11 features we constructed 11 DNN models and 4 traditional statistical models and then compared their performances and analysed feature importance for interpreting DNN models.

RESULTS

The area under the receiver operating characteristic curve, accuracy, Youden's index, F1 score, sensitivity, specificity, positive predictive value and negative predictive value, were 0.960, 0.897, 0.794, 0.897, 0.883, 0.911, 0.914, and 0.882, respectively, for our best model, and compared with the traditional statistical model based on the mean corpuscular volume, these values were increased by 10.22%, 10.09%, 26.55%, 8.92%, 4.13%, 16.90%, 13.86% and 6.07%, respectively, and by 15.38%, 11.70%, 31.70%, 9.89%, 3.05%, 22.13%, 17.11% and 5.94%, respectively, for the mean cellular haemoglobin model. The DNN model performance will reduce without age, RBC distribution width (RDW), sex, or both WBC and PLT.

CONCLUSIONS

Our DNN model outperformed the current screening model. In 8 features, RDW and age were the most useful, followed by sex and the combination of WBC and PLT, the remaining nearly useless.

Additional value of red blood cell parameters in predicting uncommon α-thalassemia; experience from 10 years of α-globin gene sequencing and copy number variation analysis

INTRODUCTION

The diagnosis of rare forms of α-thalassemia requires laborious genetic analyses. Accurate sample selection for such evaluation is therefore essential. The main objectives of this study were to investigate the predictive power of red blood cell parameters to detect rare forms of α-thalassemia (substudy 1), and to explore the frequency of rare versus common forms of α-thalassemia in our sample population (substudy 2).

METHODS

In substudy 1, we reviewed all blood samples selected for extended α-hemoglobinopathy evaluation at our laboratory during 2011-2020 (n = 1217), which included DNA sequencing and/or copy number variation analysis. We assessed α-thalassemia positive samples at different levels of mean corpuscular hemoglobin (MCH) alone and in combination with results for red blood cell count (RBC) or red cell distribution width (RDW). In substudy 2, we examined the distribution of α-thalassemia genotypes for all samples submitted to a first-tier hemoglobinopathy evaluation at our laboratory during 2014-2020 (n = 6495).

RESULTS

In substudy 1, both RBC and RDW added predictive value in detecting rare forms of α-thalassemia in samples from adults and children. In adult samples with MCH ≤ 23 pg, the presence of erythrocytosis increased the detection rate from 27% to 74% as compared to non-erythrocytosis, while normal RDW increased the detection rate from 36% to 86% as compared to elevated RDW. In substudy 2, rare forms of α-thalassemia were detected in 12% of α-thalassemia positive samples.

CONCLUSION

Initial assessment of MCH, RBC, and RDW provided valuable predictive information about the presence of rare forms of α-thalassemia during hemoglobinopathy evaluation.

Molecular Basis and Genetic Modifiers of Thalassemia

Thalassemia syndromes are common monogenic disorders and represent a significant health issue worldwide. In this review, the authors elaborate on fundamental genetic knowledge about thalassemias, including the structure and location of globin genes, the production of hemoglobin during development, the molecular lesions causing α-, β-, and other thalassemia syndromes, the genotype-phenotype correlation, and the genetic modifiers of these conditions. In addition, they briefly discuss the molecular techniques applied for diagnosis and innovative cell and gene therapy strategies to cure these conditions.

Detection of four rare thalassemia variants using Single-molecule realtime sequencing

Conventional methods for the diagnosis of thalassemia include gap polymerase chain reaction (Gap-PCR), reverse membrane hybridization (RDB), multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing. In this study, we used single molecule real-time technology (SMRT) sequencing and discovered four rare variants that have not been identified by conventional diagnostic methods for thalassemia. We also performed genotype and phenotype analyses on family members of thalassemia patients. The SMRT technology detected five cases in which the proband had abnormal results by conventional diagnostic methods or inconsistencies between the genotype and phenotype. The variants included two cases of an α-globin gene cluster 27,311 bp deletion, --^27.3/αα (hg38 chr16:158664-185974), one case of an HS-40 region 16,079 bp deletion (hg38 chr16:100600-116678), one case of a rearrangement of -α^3.7α1α2 on one allele and one case of a ß-globin gene cluster HBG1-HBG2 4,924 bp deletion (hg38 chr11:5249345-5254268). This study clarified the hematological phenotypes of four rare variants and indicated the application value of SMRT in the diagnosis of rare α-globin and ß-globin gene cluster deletions, gene recombination and deletion breakpoints. The SMRT method is a comprehensive one-step technology for the genetic diagnosis of thalassemia and is particularly suitable for the diagnosis of thalassemia with rare deletions or genetic recombination.

Advances in screening of thalassaemia

Thalassaemia is a common hereditary haemolytic anaemia. Mild cases of this disease may be asymptomatic, while patients with severe thalassaemias require high-dose blood transfusions and regular iron removal to maintain life or haematopoietic stem cell transplantation to be cured, imposing an enormous familial and social burden. Therefore, early, timely, and accurate screening of patients is of great importance. In recent years, with the continuous development of thalassaemia screening technologies, the accuracy of thalassaemia screening has also improved significantly. This article reviews the current research on thalassaemia screening.

The hemoglobinopathies, molecular disease mechanisms and diagnostics

Hemoglobinopathies are the most common monogenic disorders in the world with an ever increasing global disease burden each year. As most hemoglobinopathies show recessive inheritance carriers are usually clinically silent. Programmes for preconception and antenatal carrier screening, with the option of prenatal diagnosis are considered beneficial in many endemic countries. With the development of genetic tools such as Array analysis and Next Generation Sequencing in addition to state of the art screening at the hematologic, biochemic and genetic level, have contributed to the discovery of an increasing number of rare rearrangements and novel factors influencing the disease severity over the recent years. This review summarizes the basic requirements for adequate carrier screening analysis, the importance of genotype–phenotype correlation and how this may lead to the unrevealing exceptional interactions causing a clinically more severe phenotype in otherwise asymptomatic carriers. A special group of patients are β‐thalassemia carriers presenting with features of β‐thalassemia intermedia of various clinical severity. The disease mechanisms may involve duplicated α‐globin genes, mosaic partial Uniparental Isodisomy of chromosome 11p15.4 where the HBB gene is located or haplo‐insufficiency of a non‐linked gene SUPT5H on chromosome 19q, first described in two Dutch families with β‐thalassemia trait without variants in the HBB gene.

Hb Wanjiang: A New β-Globin Chain Variant with Two Amino Acid Substitutions (HBB: c.255_264delinsTTTTTCTCAG)

We report a new hemoglobin (Hb) variant that we have named Hb Wanjiang (HBB: c.255_264delinsTTTTTCTCAG). We identified this variant in a Chinese man by the next-generation sequencing (NGS) method. The father of the proband also carried the same variant. This variant results from a 10 bp deletion at codons 84-87 of the β-globin chain, replaced with 10 nucleotides coming from the δ-globin gene at the same position, leading to the substitution of two amino acids in the peptide chain with no change in the β-globin chain length. The heterozygotes had a normal hematological feature with no abnormal Hb variant detectable on capillary electrophoresis (CE) and high performance liquid chromatography (HPLC). The combination of Hb Wanjiang and β-thalassemia (β-thal) was not found to aggravate anemia.

Hb Laibin [β96(FG3)Leu→Arg; HBB: c.290T>G]: A Novel Hemoglobin Variant Described in a Chinese Family

We report a novel β chain hemoglobin (Hb) variant found in a Chinese family. A high level of Hb F was observed on capillary electrophoresis (CE). However, high performance liquid chromatography (HPLC) showed a high level of Hb A₂. DNA sequencing revealed a single base substitution (T>G) at codon 96 of exon 2 of the β-globin gene. This alters the normally encoded leucine to arginine [β96(FG3)Leu→Arg; HBB: c.290T>G] that we propose to name Hb Laibin for the region of origin of the proband. The pedigree study showed that it was inherited from his mother.

A novel 4.9 Kb deletion at beta-globin gene is identified by the third-generation sequencing: case report from Baoan, China

BACKGROUND

Thalassemia is a common inherited haemoglobin disorder worldwide, several methods have been utilized in the step-wise screening. Even though hundreds of mutations in globin genes have been reported, novel mutations are continuously emerging as the development of DNA sequencing.

METHODS

The case is a 27-year-old female with abnormal values of routine hematological indices, who was admitted for genetic screening of thalassemia. Genomic DNA was extracted and used for genetic assays cover 26 mutations in HBA and HBB genes: gap-PCR and agarose gel electrophoresis were performed to detect deletions, while PCR-reverse dot blot was used to detect point mutations. The next- and third- generation sequencing were used to identify the known and potential novel genotypes of thalassemia, and multiplex ligation-dependent probe amplification (MLPA) was used for genotype validation.

RESULTS

Hematological results indicate microcytic hypochromic anemia, high HbA2 (7.2%) and high HbF (6.2%). None of the known genotypes of thalassemia were matched for this case, but a novel 4.9 Kb deletion at HBB gene (hg38, Chr11: 5226187-5231089) was discovered by the third-generation sequencing, the novel deletion was also validated by MLPA (8 probes, 11p15.4: 203314-207652).

CONCLUSIONS

This study suggests the third-generation sequencing has promising potentiality to discover novel genotypes (especially deletions) of thalassemia.

Applications of next generation sequencing in the screening and diagnosis of thalassemia: A mini-review

Thalassemias are a group of inherited blood disorders that affects 5-7% of the world population. Comprehensive screening strategies are essential for the management and prevention of this disorder. Today, many clinical and research laboratories have widely utilized next-generation sequencing (NGS) technologies to identify diseases, from germline and somatic disorders to infectious diseases. Yet, NGS application in thalassemia is limited and has just recently surfaced due to current demands in seeking alternative DNA screening tools that are more efficient, versatile, and cost-effective. This review aims to understand the several aspects of NGS technology, including its most current and expanding uses, advantages, and limitations, along with the issues and solutions related to its integration into routine screening and diagnosis of thalassemias. Hitherto, NGS has been a groundbreaking technology that offers tremendous improvements as a diagnostic tool for thalassemia in terms of its higher throughput, accuracy, and adaptability. The superiority of NGS in detecting rare variants, solving complex hematological problems, and providing non-invasive alternatives to neonatal diagnosis cannot be overlooked. However, several pitfalls still preclude its use as a stand-alone technique over conventional methods.

The Editor's Choice for Issue 3, Volume 7

Dear Readers: Choosing one paper from a total of 28 papers published in the third issue of Volume 7 was quite a challenge [...].