Non-deletional alpha thalassaemia: a review

A rare -α27.6 deletion compounded with the hemoglobin constant spring mutation identified in a Chinese couple

BACKGROUND

Thalassemia is a common hemoglobin disorder caused by genetic defects in a single autosomal gene. Based on the deficient globin strand, it can be classified as α-thalassemia or β-thalassemia. The 27.6 kb deletion on α-globin related gene cluster (-α27.6) is a rare α-thalassemia variant discovered in 2011, which could affect the detection of common α-thalassemia variants and cause misdiagnosis.

CASE PRESENTATION

An α-thalassemia variant carrying a Chinese couple was reported in this study. The wife was diagnosed at another hospital as αCSα/αCSα but did not manifest corresponding symptoms. After further examinations and in-depth analyses of the results, the genotype of the wife was finally confirmed to be -α27.6/αCSα. Meanwhile, the genotype of the husband was diagnosed as αCSα/αα. The couple requested prenatal diagnosis in the worry of α-thalassemia caused by αCSα/αCSα. Genetic tests on the amniotic fluid reported a mild thalassemia-related genotype of αCSα/αα, on which our suggestion of continuing pregnancy was based.

CONCLUSION

The -α27.6/αCSα case and related manifestations were first reported here expanding the gene spectrum of thalassemia. Such genotype can be misdiagnosed as αCSα/αCSα causing inaccurate estimations of thalassemia risk. To avoid these misdiagnoses, genetic tests for deletions in the related regions were advised when inconsistencies between the genotype and the phenotype were discovered.

A sample-in- result -out microfluidic system for β-thalassemia diagnostics via direct whole blood PCR-reverse dot blot

OBJECTIVE

Existing thalassemia detection methods demand high - end labs and have complex procedures, leading to long testing cycles. This study aims to develop a convenient detection method integrated with a microfluidic platform for a sample - to - result process.

METHOD

First, optimal conditions for the whole blood direct PCR - reverse dot hybridization (dPCR - RDB) system were explored. Then, its performance was evaluated with clinical samples. Finally, the entire process was integrated into a palm - sized microfluidic chip for "sample - in, result - out" detection.

RESULT

A stable dPCR - RDB system was established. Clinical verification on 149 samples showed a 0.1 μl whole - blood minimum detection limit, 100 % specificity, and resistance to high triglyceride and bilirubin levels. It had 100 % positive and negative coincidence rates with traditional methods (kappa = 1). The microfluidic - integrated platform achieved "sample - in, result - out" with 0.5-1 μl blood in 130 min, sans a PCR lab.

CONCLUSION

A "sample - in, result - out" microfluidic gene detection platform using whole blood as the template was successfully established.

Snrnp25 is a candidate for the peri-implantation lethal phenotype of the Hba deletions

Mutations in adult hemoglobin alpha genes in humans lead to blood disorders commonly known as α-thalassemia. In search of a mouse model for this disease, mutagenesis screens have identified several deletions that resemble these phenotypes. The Hbab2(th) deletion, in particular, replicates the characteristics of alpha-thalassemia minor in heterozygous mice but presents a homozygous embryonic lethal phenotype. Previous analyses of Hbab2(th) mice suggested that the deletion affects both Hba genes (Hba-a1 and Hba-a2) and considered epidermal growth factor receptor (Egfr) or rhomboid 5 homolog 1 (Rhbdf1) to be responsible for the embryonic lethality. Molecular analysis of Hbab2(th) revealed a deletion spanning a 1 cM region of mouse chromosome 11. Importantly, the Hbab2(th) deletion does not extend to Egfr, indicating that the observed lethality of homozygous embryos is not due to the loss of Egfr. Sequence analysis of the Hbab2(th) deletion showed that the Hba-a2 gene is not deleted, but the lack of expression is likely due to the disruption of upstream regulatory regions. Furthermore, we identify Snrnp25, which codes for the small nuclear ribonucleoprotein 25 (U11/U12), as the candidate gene most likely responsible for the peri-implantation lethality of Hbab2(th) homozygous mice. These findings enhance the understanding of the genetic mechanisms underlying α-thalassemia and provide insights into novel genes essential for early mammalian development.

The Clinical and Laboratory Profiles of a Deletional α2-Globin Gene Polyadenylation Signal Sequence (AATAAA > AATA--) [HBA2:c.*93_*94delAA]: The Malaysian Experience

Poly A (AATAAA > AATA--) [HBA2:c.*93_*94delAA] is a rare α-variant reported in our population. It is caused by 2 bp deletion (--AA) in the α2 poly A sequence, leading to a significant α-thalassaemia phenotype. Background/Objectives: This study describes the haematological parameters, phenotype, and genotype characteristics of AATA(--AA) in the Malaysian population. Methods: The study was carried out on 17 177 cases referred to the Institute for Medical Research, Malaysia, for further diagnosis of α-thalassaemia in a five-year period. Alpha-Gap and ARMS-PCR were performed to detect common α-thalassaemia, followed by HBA1 and HBA2 genes sequencing and multiplex ligation-dependent probe amplification (MLPA). Haematological parameters among various groups with the AATA(--AA) allele were presented in this study. Results: Thirty-two patients with AATA(--AA) displaying an α-thalassaemia-like phenotype were analysed. They comprised 22 (68.75%) AATA(--AA) carriers, 2 (6.25%) compounds with 3.7 deletion, 2 (6.25%) compounds with --SEA deletion, 1 (3.12%) AATA(--AA) homozygote, and 3 (9.37%) compounds of Hb Adana, Hb CS, and Hb Pakse with co-inheritance Hb E, respectively. Most of the patients with AATA(--AA) compounds with the α-variant exhibited a significant phenotype between moderate to severe thalassaemia, especially cases with compound α-AAα/αAdanaα. Conclusions: AATA(--AA) is a significant pathogenic variant that should be diagnosed to prevent significant thalassaemia phenotype or transfusion-dependent thalassaemia.

Comprehensive analysis of a-and b-thalassemia genotypes and hematologic phenotypes

Background

Guizhou Province is an area with high incidence of thalassemia. However, there are few large-sample studies on the correlation between genotypes and phenotypes in Guizhou Province. In this study, the phenotypes and genotypes of 1174 patients with thalassemia in Guizhou Province were collected, and the relationship between different genotypes and phenotypes was analyzed, providing a more accurate basis for genetic counseling, prevention and control of thalassemia.

Methods

A total of 1174 patients with thalassemia were collected in Guizhou Provincial People's Hospital from October 2020 to December 2021 by PCR-reverse dot blot (RDB) hybridization assay, and their red blood cell (RBC), hemoglobin (Hb), mean erythrocyte volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), red blood cell distribution width (RDW), hemoglobin (HbA), hemoglobin A2 (HbA2), and fetal hemoglobin (HbF) data were collected. The relationship between different genotypes and phenotypes was analyzed.

Results

Among 1174 cases of thalassemia or carriers, there were 617 cases of a-thalassemia, 512 cases of b-thalassemia, 45 cases of coinheritance of aand b-tha-lassemia. The severity of anemia between a-thalassemia was positively correlated with the decrease of non-functional copy number of a-globin gene. The degree of anemia in non-deletion a-thalassemia was greater than that in deletion a-thalassemia. In b-thalassemia, b0 gene mutation did not produce b-globin, and b+ mutation expressed some bglobin, but it was lower than normal level. b0/b0 had no bglobin production, and long-term blood transfusion was required to maintain life. Compared with a-thalassemia, the degree of anemia in b-thalassemia whose clinical type was same as a-thalassemia was more serious. The anemia degree of coinheritance of aand b-thalassemia was less than that of simple a-thalassemia or b-thalassemia.

Conclusions

The clinical phenotype of thalassemia is influenced by molecular mechanism, and the two kinds of thalassemia can interact with each other. The clinical severity is positively correlated with the imbalance of a peptide chain and b peptide chain. A comprehensive understanding of the hematologic phenotype differences between different genotypes and subtypes of thalassemia can provide more accurate data for genetic counseling of thalassemia.

Characterization and Confirmation of Mildly Unstable Hb Pontoise or α1 63(E12) Ala > Asp and Literature Review

Genotype-phenotype correlation and potential genetic risk in the compound heterozygosity for unstable hemoglobins (UHbs) and α0-thalassemia were discussed. Capillary electrophoresis and gene sequencing helped to establish the diagnosis. Hematological analysis showed the following findings: MCV 80.6 fL, MCH 27 pg, HGB 133 g/L, RBC 4.93 × 1012/L, Hb A: 94%, Hb X: 3.6% (zone 12) and Hb A2: 2.4%. DNA analysis revealed the patient was a Hb Pontoise carrier (HBA1: c.191C > A). Hb Pontoise resulted from an GCC > GAC substitution at codon 63 of the HBA1 genes, but carriers were usually asymptomatic or with only borderline hematological abnormalities. Due to mild instability of Hb Pontoise, its diagnosis relied on genetic diagnosis. Considering the high frequency of thalassemia in South China, accurate genotyping and appropriate genetic counseling should be performed for unstable hemoglobin carriers.

Hb SKMC and an unprecedented γδβ-thalassemia: first report from Iraq

BACKGROUND

Thalassemias are genetic disorders of globin chain synthesis. In Iraq, β-thalassemia is more prevalent than α-thalassemia. This study identifies two unpredicted globin gene mutations, a rare α-globin gene mutation (Hb SKMC) and a novel γδβ-thalassemia deletion.

METHODS

Over 2 years, the Genetics unit at PAR hospital in Erbil, northern Iraq processed 137 β-thalassemia and 97 α-thalassemia genetic testing requests. Three symptomatic thalassemia cases with unreported genotypes were identified. Proband-1α and proband-2α had Hb H disease, while proband-1β had severe transfusion-dependent β-thalassemia (TDT). Molecular studies included multiplex PCR, reverse hybridization, multiplex ligation-dependent probe amplification (MLPA), and globin gene sequencing.

RESULTS

The α-thalassemia probands exhibited moderate microcytic hypochromic anemia with irregular transfusions and splenomegaly. Hb H disease was confirmed by positive Hb H tests and high-performance liquid chromatography (HPLC). Molecular analysis revealed heterozygous -MED deletion in proband-1α and α2Poly-A2 mutation in proband-2α. Sequencing identified the Hb SKMC (HBA1:c.283_300+3dup) mutation in both probands. The β-thalassemia proband showed anemia and regular transfusions. Molecular studies detected the IVS1.110 G>A mutation and a novel γδβ-thalassemia deletion in compound heterozygous form. The maternal sample showed the IVS1.110 G>A mutation, and MLPA confirmed the γδβ-thalassemia deletion in the paternal sample.

CONCLUSION

These findings highlight the genetic diversity of thalassemias in the region and emphasize the importance of advanced molecular diagnostics in detecting rare mutations.

Microcolumn and coelution hydration of oil seal blood spot for efficient screening of newborn α-thalassemia via chip isoelectric focusing

BACKGROUND

The global prevalence of α-thalassemia necessitates effective newborn screening strategies due to its severe clinical consequences. Traditional methods such as liquid chromatography (LC), capillary electrophoresis (CE), and isoelectric focusing (IEF) face limitations, including low separation efficiency, poor sensitivity for detecting Hb Bart's, and time-intensive operations, particularly with dried blood spots (DBS). These limitations hinder timely and accurate screening. This study addresses the need for a more efficient, sensitive, and rapid method for detecting Hb Bart's in newborns.

RESULTS

We enhanced IEF separation and sensitivity by designing a microfluidic IEF (mIEF) system with shortened columns and employing a coelution sample loading technique using oil-sealed blood spots for rapid sample pretreatment. Our experiments demonstrated significant improvements: the total analysis time was reduced from 1110 min (IPG IEF) and 46 min (LC) per batch to 36 min per batch. For individual samples, the focusing time decreased from 6 min (previous mIEF) to 3 min, with the microcolumn length shortened by 50 %, from 30 mm to 15 mm. The developed method showed excellent consistency with clinical Bart's detection and PCR diagnosis, achieving 100 % sensitivity and 98 % specificity for α-thalassemia screening.

SIGNIFICANCE AND NOVELTY

Our novel mIEF method provides an efficient, sensitive, and rapid tool for screening newborns for α-thalassemia. This advancement addresses the limitations of traditional techniques, improving early diagnosis and intervention strategies and ultimately enhancing health outcomes for at-risk newborns.

The Most Common Types of 3.7 Kilobase Deletion in the Iranian Population

The 3.7 kb deletion is the most common known mutation in the α-globin gene cluster worldwide. The aim of this study is to investigate the most common types of 3.7 kb deletions in the Iranian population and, on the other hand, to compare the extent of deletion of the different reported types.

In this study, 50 Iranian α-thalassemia carriers in whom the 3.7 kb deletion had been previously identified by multiplex gap PCR, were further investigated by MLPA. A map of the region where the 3.7 kb deletion occurs was also created and the extents of the reported types were compared.

Approximately 90% of chromosomes with 3.7 kb deletion in this study had MLPA type D and 10% had MLPA type F. This study showed that subtype I of the 3.7 kb deletion reported by Higgs and his coworkers can be classified into at least 5 MLPA types.

The results of this study can be used to complete the information on the distribution of the 3.7 kb deletion subtypes in different populations. Investigation of further populations using higher resolution methods may lead to more information being obtained in this field.

Use of HSC-targeted LNP to generate a mouse model of lethal α-thalassemia and treatment via lentiviral gene therapy

ABSTRACT

α-Thalassemia (AT) is one of the most commonly occurring inherited hematological diseases. However, few treatments are available, and allogeneic bone marrow transplantation is the only available therapeutic option for patients with severe AT. Research into AT has remained limited because of a lack of adult mouse models, with severe AT typically resulting in in utero lethality. By using a lipid nanoparticle (LNP) targeting the receptor CD117 and delivering a Cre messenger RNA (mRNACreLNPCD117), we were able to delete floxed α-globin genes at high efficiency in hematopoietic stem cells (HSC) ex vivo. These cells were then engrafted in the absence or presence of a novel α-globin-expressing lentiviral vector (ALS20αI). Myeloablated mice infused with mRNACreLNPCD117-treated HSC showed a complete knock out (KO) of α-globin genes. They showed a phenotype characterized by the synthesis of hemoglobin H (HbH; also known as β-tetramers or β4), aberrant erythropoiesis, and abnormal organ morphology, culminating in lethality ∼8 weeks after engraftment. Mice infused with mRNACreLNPCD117-treated HSC with at least 1 copy of ALS20αI survived long term with normalization of erythropoiesis, decreased production of HbH, and amelioration of the abnormal organ morphology. Furthermore, we tested ALS20αI in erythroid progenitors derived from α-globin-KO CD34+ cells and cells isolated from patients with both deletional and nondeletional HbH disease, demonstrating improvement in α-globin/β-globin mRNA ratio and reduction in the formation of HbH by high-performance liquid chromatography. Our results demonstrate the broad applicability of LNP for disease modeling, characterization of a novel mouse model of severe AT, and the efficacy of ALS20αI for treating AT.

A rare hemoglobinopathy duo: Hb Adana×Hb SEA in a 1-year-old patient - a case report and a brief literature review

Introduction and importance

Alpha thalassemia, resulting from nondeletional mutations, typically presents a more severe clinical manifestation compared to deletional mutations. Severe outcomes, such as hydrops fetalis, are associated with two specific nondeletional mutations. Therefore, DNA-based investigation is crucial for suspected carriers exhibiting subtle hematological abnormalities to facilitate proper diagnosis and effective family counseling.

Case presentation

In this report, the authors describe a phenotypically normal 1-year-old girl with a rare and unique alpha-thalassemia genotype due to the presence of Hb Adana, a nondeletional alpha-chain mutation compounded with Hb SEA, an alpha-globin gene deletion.

Clinical discussion

Mutations determine the clinical manifestations of alpha-thalassemia. DNA testing is recommended for suspected carriers with relatively small hematological abnormalities, for precise diagnosis and family counseling. To provide clinicians with a reference for diagnostic assessment, the authors established a genotype-phenotype correlations based on reported cases of Hb Adana following an exhaustive literature review. Being interested in determining which ethnicities and genotypes are associated with a higher risk of complications, including hydrops fetalis and transfusion dependence, the authors formalized a diagnostic evaluation guide and a guide for early screening to improve outcomes.

Conclusion

Precise genetic evaluation is important for the diagnosis of alpha thalassemia. Hematologists play a critical role in managing these disorders, understanding genotype-phenotype correlations, and highlighting the significance of genetic counseling for high-risk patients. Extensive studies on these various genophenotypes are required to improve the diagnosis and prognosis of such medical conditions and advocate preventative strategies.

Uncommon Combination of Hemoglobin Jax and Hemoglobin Constant Spring Leading to Microcytic Anemia

BACKGROUND Thalassemia and hemoglobin (Hb) variants are the most common hereditary red blood cell disorders worldwide. Alpha-thalassemia and alpha-globin variants are caused by mutations of the alpha-globin genes (HBA2 and HBA1), resulting in impaired alpha-globin production and structurally abnormal globin, respectively. Clinical severity of alpha-thalassemia correlates with the number of affected alpha-globin genes, yielding a spectrum of clinical manifestations from mild to severe anemia. Routine diagnosis involves Hb analysis and PCR-based methods, yet identifying rare variants necessitates comprehensive clinical and hematologic laboratory data. The knowledge of phenotype and genotype correlation is useful for genetic counseling and treatment planning. CASE REPORT A 59-year-old Thai woman presented with chronic anemia. Her baseline Hb level ranged between 8.0 and 9.0 g/dL, with no history of transfusion. Physical examination showed mild pallor, without enlarged liver and spleen. Laboratory investigations showed microcytic, hypochromic anemia and abnormal Hb peak by Hb analysis (retention time 4.58 min by HPLC method). Common alpha-globin gene deletions, including the Southeast-Asian/Thai 3.7 kb and 4.2 kb deletions were tested using gap-PCR, with none of these deletions detected. Direct DNA sequencing revealed a compound heterozygosity of Hb Jax (HBA2: c.44G>C) and Hb Constant Spring (HBA2: c.427T>C). CONCLUSIONS Compound heterozygosity of Hb Jax and Hb Constant Spring results in microcytic anemia. Hb Jax can be identified by Hb analysis, and diagnosis can be confirmed by direct DNA sequencing method. Coinheritance of Hb Jax and alpha-globin variants should be considered in cases with microcytic anemia and a specific Hb peak seen in Hb chromatogram.

Neonatal Screening for Sickle Cell Disease in Western Andalusia: Results and Lessons Learnt after 3 Years of Implementation

OBJECTIVE

The aim of this study was to present the results obtained in the Newborn Screening Program (NSP) for sickle cell disease (SCD) in western Andalusia and the autonomous city of Ceuta in the first 3 years of implementation, and to describe the discrepancies found in the diagnosis of hemoglobinopathies between the screening method and the confirmatory tests.

STUDY DESIGN

A descriptive and retrospective study was carried out, and the findings obtained in the newborns included in the NSP between November 2018 and December 2021 were analyzed.

RESULTS

A total of 111,205 samples were screened by high-performance liquid chromatography (HPLC). The birth prevalence of SCD, sickle cell trait, hemoglobin C carriers, and the compound heterozygosity Hb C/β-thalassemia was 1/12,356, 1/467, 1/1,278, and 1/55,602 newborns, respectively. Although there was a correlation between the first-line HPLC screening technique (VARIANTnbs HPLC analyzer, Bio-Rad) and the confirmatory tests in most cases, major discrepancies were found in detecting carriers of G-Philadelphia, D, E, and O-Arab hemoglobin variants, with the former having an incidence of 1/10,110 and the others 1/22,241. The carrier status of Hb G-Philadelphia produced an FAD pattern on the screening method that could be mistaken as Hb D, while Hb O-Arab was identified as an FA5 pattern. Hb D was initially recognized as Hb D in two cases.

CONCLUSION

An NSP requires at least two different combined methods in order to identify the hemoglobin variant with sufficient certainty. Furthermore, even though software solutions for HPLC suggest a pattern, it must be confirmed with another technique to obtain a correct interpretation of the chromatograms.

KEY POINTS

· The NSPs are an essential activity in preventive medicine.. · At least two different combined methods are required to correctly identify hemoglobin variants.. · Different variants can produce a similar or identical pattern by a single method..

A Novel Frameshift Mutation(HBA2:C.337delC) Associated With α-Thalassemia Trait Detected by Next-Generation Sequencing in Southern China

Here, we report a novel frameshift mutation caused by a single base deletion in exon 3 of the HBA2 gene (HBA2:c.337delC) detected by next-generation sequencing. The proband was a 26-year-old Chinese pregnant woman who originates from Hunan Province. Her mean corpuscular volume(MCV) and mean corpuscular hemoglobin (MCH) had a mild decrease. Capillary electrophoresis (CE) showed that both Hb A (97.8%) and Hb F (0.0%) values were within normal range, while the Hb A2 (2.2%) value was below normal. Sequence analysis of the α and β-globin genes revealed a novel single base deletion at codon 112 (HBA2:c.337delC) in the heterozygous state, which resulted in a mild phenotype of α-thalassemia.

Αlpha-thalassemia: A practical overview

α-Thalassemia is an inherited blood disorder characterized by decreased synthesis of α-globin chains that results in an imbalance of α and β globin and thus varying degrees of ineffective erythropoiesis, decreased red blood cell (RBC) survival, chronic hemolytic anemia, and subsequent comorbidities. Clinical presentation varies depending on the genotype, ranging from a silent or mild carrier state to severe, transfusion-dependent or lethal disease. Management of patients with α-thalassemia is primarily supportive, addressing either symptoms (eg, RBC transfusions for anemia), complications of the disease, or its transfusion-dependence (eg, chelation therapy for iron overload). Several novel therapies are also in development, including curative gene manipulation techniques and disease modifying agents that target ineffective erythropoiesis and chronic hemolytic anemia. This review of α-thalassemia and its various manifestations provides practical information for clinicians who practice beyond those regions where it is found with high frequency.

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.

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.

Prime editing: A potential treatment option for β-thalassemia

The potential to therapeutically alter the genome is one of the remarkable scientific developments in recent years. Genome editing technologies have provided an opportunity to precisely alter genomic sequence(s) in eukaryotic cells as a treatment option for various genetic disorders. These technologies allow the correction of harmful mutations in patients by precise nucleotide editing. Genome editing technologies such as CRISPR (clustered regularly interspaced short palindromic repeat) and base editors have greatly contributed to the practical applications of gene editing. However, these technologies have certain limitations, including imperfect editing, undesirable mutations, off-target effects, and lack of potential to simultaneously edit multiple loci. Recently, prime editing (PE) has emerged as a new gene editing technology with the potential to overcome the above-mentioned limitations. Interestingly, PE not only has higher specificity but also does not require double-strand breaks. In addition, a minimum possibility of potential off-target mutant sites makes PE a preferred choice for therapeutic gene editing. Furthermore, PE has the potential to introduce insertion and deletions of all 12 single-base mutations at target sequences. Considering its potential, PE has been applied as a treatment option for genetic diseases including hemoglobinopathies. β-Thalassemia, for example, one of the most significant blood disorders characterized by reduced levels of functional hemoglobin, could potentially be treated using PE. Therapeutic reactivation of the γ-globin gene in adult β-thalassemia patients through PE technology is considered a promising therapeutic strategy. The current review aims to briefly discuss the genome editing strategies and potential applications of PE for the treatment of β-thalassemia. In addition, the review will also focus on challenges associated with the use of PE.

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.

Identification of a novel 10.3 kb deletion causing α0-thalassemia by third-generation sequencing: Pedigree analysis and genetic diagnosis

BACKGROUND

α-thalassemia is an inherited blood disorder caused by variants in the α-globin gene cluster. Identification of the pathogenic α-globin gene variants is important for the diagnosis and management of thalassemia.

METHODS

Two suspected families from Xiantao, Hubei Province were recruited in this study. The family members underwent hemoglobin testing. Polymerase Chain Reaction based reverse dot blot (PCR-RDB) was employed to identify the known variants. Next-generation sequencing (NGS) and third-generation sequencing (TGS) were performed to screen the potential disease-causing variants, which were validated by Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA).

RESULTS

Hematological analysis suggested that proband A had α-thalassemia traits, and proband B had HbH disease traits. However, only a -α^3.7 mutation had been detected by PCR-RDB and NGS in the proband of family B. Subsequent TGS identified a novel 10.3 kb deletion (NC_000016.10:g.172342-182690del) covering the HBA1, HBQ1 and HBA2 genes in the α-globin gene cluster in both family A and B, which was confirmed by Sanger sequencing and MLPA. These results indicated that the novel deletion is likely responsible for α-thalassemia.

CONCLUSION

A novel α-thalassemia deletion was identified for the two families by TGS. Our work broadened the molecular spectrum of α-thalassemia, and was beneficial for the diagnosis, genetic counseling and management of α-thalassemia.

Gene Mutation Spectrum among Alpha-Thalassaemia Patients in Northeast Peninsular Malaysia

(1) Background: Alpha (α)-thalassaemia is a genetic disorder that affects 5% of the world population. Deletional or nondeletional mutations of one or both HBA1 and HBA2 on chromosome 16 will result in reduced production of α-globin chains, a component of haemoglobin (Hb) that is required for the formation of red blood cells (RBCs). This study aimed to determine the prevalence, haematological and molecular characterisations of α-thalassaemia. (2) Method: The parameters were based on full blood count, high-performance liquid chromatography and capillary electrophoresis. The molecular analysis involved gap-polymerase chain reaction (PCR), multiplex amplification refractory mutation system-PCR, multiplex ligation-dependent probe amplification and Sanger sequencing. (3) Results: With a total cohort of 131 patients, the prevalence of α-thalassaemia was 48.9%, leaving the remaining 51.1% with potentially undetected α gene mutations. The following genotypes were detected: -α^3.7/αα (15.4%), -α^4.2/αα (3.7%), --^SEA/αα (7.4%), α^CSα/αα (10.3%), α^Adanaα/αα (0.7%), α^{Quong Szeα}/αα (1.5%), -α^3.7/-α^3.7 (0.7%), α^CSα/α^CSα (0.7%), -α^4.2/α^CSα (0.7%), -^SEA/α^CSα (1.5%), -^SEA/α^{Quong Sze}α (0.7%), -α^3.7/α^Adanaα (0.7%), --^SEA/-α^3.7 (2.2%) and α^CSα/α^Adanaα (0.7%). Indicators such as Hb (p = 0.022), mean corpuscular volume (p = 0.009), mean corpuscular haemoglobin (p = 0.017), RBC (p = 0.038) and haematocrit (p = 0.058) showed significant changes among patients with deletional mutations, but not between patients with nondeletional mutations. (4) Conclusions: A wide range of haematological parameters was observed among patients, including those with the same genotype. Thus, a combination of molecular technologies and haematological parameters is necessary for the accurate detection of α-globin chain mutations.

Impact of age-dependent red blood cell parameters on α-globin gene genotyping in children

When screening for α-thalassemia in children, adult cut-offs for mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) are generally applied to guide genetic evaluation. However, the normal ranges for MCV and MCH are lower in children than in adults, so we hypothesized that using age-matched cut-offs could lead to a more rational diagnostic strategy. The aim of this study was to evaluate if age-matched cut-offs could be applied advantageously. Data on children referred to a hemoglobin fractionation at the Department of Clinical Biochemistry, Aarhus University Hospital between 2016-2021 were identified in the laboratory information system. α-globin gene (HBA1/HBA2) genotyping was performed using multiplex gap-polymerase chain reaction. A total of 387 children were identified. HBA1/HBA2-genotyping was performed in 207 children (53%), and α-thalassemia was diagnosed in 47 children (23%) with -α3.7/αα being the predominant genotype (13%). We found that 23 children had MCV and MCH levels in the normal age-matched range, and two of these children (9%) were α+ thalassemia carriers with three functional α-globin genes. Using age-specific cut-off levels resulted in a reduction of 23 (11%) genotypes performed. In conclusion, applying age-matched cut-offs for MCV and MCH when screening children for α-thalassemia lead to 11% fewer genotypes performed while 9% carriers of α+ thalassemia (of the medically innocuous genotype -α3.7/αα) would have been overlooked.

Prevalence and molecular characterization of alpha and beta-Thalassemia mutations among Hakka people in southern China

Our aim was to investigate molecular features of thalassemia for proper clinical consultation and prevention in Heyuan. In our research, a total of 25,437 positive screening subjects were further subjected to a genetic analysis of α-thalassemia (α-thal) and β-thalassemia (β-thal). The deletion of α-thal mutation was tested by Gap-PCR, while the non-deletion of α-thal and β-thal mutation were identified by the PCR-reverse dot blot (PCR-RDB) technique. Nested PCR detected Hkαα/-- SEA and Hkαα/αα. Among the 25,437 positive screening subjects, 44.09% (11216/25437) subjects were bearers of thalassemia variations, and 30.85% (7847/25437) subjects showed α-thal changes alone. Among the 23 genotypes with α-thal mutation alone, the three common genotypes were --SEA/αα(68.34%), -α3.7/αα(16.44%), and -α4.2/αα(6.38%). Of the 11.50% (2924/25437) subjects and 29 genotypes with β-thal mutation alone, the three common genotypes were βCD41-42/βN(36.22%), βIVS-II-654/βN(30.88%), and β-28/βN(13.47%). Additionally, of the 1.75% (445/25437) subjects and 55 genotypes showed both α- and β-thal mutations. We also identified 269 cases of Hb H and six patients of Hkαα. Furthermore, the common genotypes of α-thal and β-thal mutations were consistent with allele frequencies of mutations. Our study establishes molecular features of thalassemia among Hakka people in Heyuan. It will be useful for developing strategies to prevent thalassemia.

Combined Gap-Polymerase Chain Reaction and Targeted Next-Generation Sequencing Improve α- and β-Thalassemia Carrier Screening in Pregnant Women in Vietnam

Vietnam has a high thalassemia burden. We collected blood samples from 5880 pregnant Vietnamese women during prenatal health checks to assess thalassemia carrier frequency using combined gap-polymerase chain reaction (gap-PCR) and targeted next-generation sequencing (NGS). Thalassemia carriers were identified with prevalence of 13.13% (772), including 7.82% (460) carriers of α-thalassemia (α-thal), 5.31% (312) carriers of β-thalassemia (β-thal), and 0.63% (37) concurrent α-/β-thal carriers. Deletional mutations (368) accounted for 80.0% of α-thal carriers, of which, --^SEA (Southeast Asian) (n = 254; 55.0%) was most prevalent, followed by the -α^3.7 (rightward) (n = 66; 14.0%) and -α^4.2 (leftward) (n = 45; 9.8%) deletions. Hb Westmead (HBA2: c.369C>G) (n = 53) and Hb Constant Spring (Hb CS or HBA2: c.427T>C) (in 28) are the two most common nondeletional α-globin variants, accounting for 11.5 and 6.0% of α-thal carriers. We detected 11 different β-thal genotypes. Hb E (HBB: c.79G>A) (in 211) accounted for 67.6% of β-thal carriers. The most common β-thal genotypes were associated with mutations at codon 17 (A>T) (HBB: c.52A>T), codons 41/42 (-TTCT) (HBB: c.126_129delCTTT), and codon 71/72 (+A) (HBB: c.217_218insA) (prevalence 0.70%, 0.68%, and 0.2%, respectively). Based on mutation frequencies calculated in this study, estimates of 5021 babies in Vietnam are affected with clinically severe thalassemia annually. Our data suggest a higher thalassemia carrier frequency in Vietnam than previously reported. We established that combining NGS with gap-PCR creates an effective large-scale thalassemia screening method that can detect a broad range of mutations.

Safety and efficacy of mitapivat, an oral pyruvate kinase activator, in adults with non-transfusion dependent α-thalassaemia or β-thalassaemia: an open-label, multicentre, phase 2 study

BACKGROUND

Patients with non-transfusion-dependent thalassaemia (NTDT), although they do not require regular blood transfusions for survival, can still accrue a heavy burden of comorbidities. No approved disease-modifying therapies exist for these patients. We aimed to investigate the safety and efficacy of mitapivat (Agios Pharmaceuticals, Cambridge, MA, USA), a pyruvate kinase activator, in adults with non-transfusion-dependent (NTD) α-thalassaemia or NTD β-thalassaemia.

METHODS

In this open-label, multicentre, phase 2 study, patients were recruited from four academic clinical study sites in Oakland, CA, and Boston, MA, USA; Toronto, ON, Canada; and London, UK. Patients were eligible if they were aged 18 years or older, with NTDT (including β-thalassaemia with or without α-globin gene mutations, haemoglobin E β-thalassaemia, or α-thalassaemia), and a baseline haemoglobin concentration of 10·0 g/dL or lower. During a 24-week core period, mitapivat was administered orally at 50 mg twice daily for the first 6 weeks followed by an escalation to 100 mg twice daily for 18 weeks thereafter. The primary endpoint was haemoglobin response (a ≥1·0 g/dL increase in haemoglobin concentration from baseline at one or more assessments between weeks 4 and 12). Efficacy and safety were assessed in the full analysis set (ie, all patients who received at least one dose of study drug). This study is registered with ClinicalTrials.gov, NCT03692052, and is closed to accrual.

FINDINGS

Between Dec 28, 2018, and Feb 6, 2020, 27 patients were screened, of whom 20 were enrolled (15 [75%] with β-thalassaemia and five [25%] with α-thalassaemia) and received mitapivat. The median age of patients was 44 years (IQR 35-56), 15 (75%) of 20 patients were female, five (25%) were male, and ten (50%) identified as Asian. 16 (80% [90% CI 60-93]) of 20 patients had a haemoglobin response (p<0·0001), five (100%) of five with α-thalassaemia and 11 (73%) of 15 with β-thalassaemia. 17 (85%) patients had a treatment-emergent adverse event, and 13 had a treatment-emergent event that was considered to be treatment related. One serious treatment-emergent adverse event occurred (grade 3 renal impairment), which was considered unrelated to study drug, resulting in discontinuation of treatment. The most commonly reported treatment-emergent adverse events were initial insomnia (ten [50%] patients), dizziness (six [30%]), and headache (five [25%]). No patients died during the 24-week core period.

INTERPRETATION

These efficacy and safety results support the continued investigation of mitapivat for the treatment of both α-thalassaemia and β-thalassaemia.

FUNDING

Agios Pharmaceuticals.

Anemia in the pediatric patient

The World Health Organization estimates that approximately a quarter of the world's population suffers from anemia, including almost half of preschool-age children. Globally, iron deficiency anemia is the most common cause of anemia. Other important causes of anemia in children are hemoglobinopathies, infection, and other chronic diseases. Anemia is associated with increased morbidity, including neurologic complications, increased risk of low birth weight, infection, and heart failure, as well as increased mortality. When approaching a child with anemia, detailed historical information, particularly diet, environmental exposures, and family history, often yield important clues to the diagnosis. Dysmorphic features on physical examination may indicate syndromic causes of anemia. Diagnostic testing involves a stepwise approach utilizing various laboratory techniques. The increasing availability of genetic testing is providing new mechanistic insights into inherited anemias and allowing diagnosis in many previously undiagnosed cases. Population-based approaches are being taken to address nutritional anemias. Novel pharmacologic agents and advances in gene therapy-based therapeutics have the potential to ameliorate anemia-associated disease and provide treatment strategies even in the most difficult and complex cases.

NGS4THAL, a one-stop molecular diagnosis and carrier screening tool for thalassemia and other hemoglobinopathies by next-generation sequencing

Thalassemia is one of the most common genetic diseases and a major health threat worldwide. Accurate, efficient and scalable analysis of next-generation sequencing (NGS) data is much needed for its molecular diagnosis and carrier screening. We developed NGS4THAL, a bioinformatics analysis pipeline analyzing next generation sequencing (NGS) data to detect pathogenic variants for thalassemia and other hemoglobinopathies. NGS4THAL realigns ambiguously mapped NGS reads derived from the homologous hemoglobin gene clusters for accurate detection of point mutations and small insertion/deletions (InDels). It uses a combination of complementary structural variant (SV) detection tools and an inhouse database of control data containing specific SVs to achieve accurate detection of the complex SV types. Detected variants are matched with those in HbVar database, allowing recognition of known pathogenic variants, including disease modifiers. Tested on simulation data, NGS4THAL achieved high sensitivity and specificity. For targeted NGS sequencing data from samples with laboratory-confirmed pathogenic hemoglobin variants, it achieved 100% detection accuracy. Application of NGS4THAL on whole genome sequencing data from unrelated studies revealed thalassemia mutation carrier rates for Hong Kong Chinese and Northern Vietnamese that were consistent with previous reports. NGS4THAL is a highly accurate and efficient molecular diagnosis tool for thalassemia and other hemoglobinopathies based on tailored analysis of NGS data and is potentially scalable for population carrier screening.

Diagnostic value of fetal hemoglobin Bart's for evaluation of fetal α-thalassemia syndromes: application to prenatal characterization of fetal anemia caused by undiagnosed α-hemoglobinopathy

Background

To evaluate whether the quantification of fetal hemoglobin (Hb) Bart’s is useful for differentiation of α-thalassemia syndromes in the fetus and to characterize the fetal anemia associated with fetal α-hemoglobinopathy.

Methods

A total of 332 fetal blood specimens collected by cordocentesis were analyzed using capillary electrophoresis and the amount of Hb Bart’s was recorded. The result was evaluated against thalassemia genotypes determined based on Hb and DNA analyses. Prenatal Hb and DNA characterization of the fetal anemia observed in two families was done.

Results

Among 332 fetuses investigated, Hb and DNA analyses identified 152 fetuses with normal genotypes. The remaining 180 fetuses carried α-thalassemia with several genotypes. Variable amounts of Hb Bart’s were identified in all fetuses with α-thalassemia, which could be used for simple differentiation of fetal α-thalassemia genotypes. These included α⁺- and α⁰-thalassemia traits, homozygous α⁺-thalassemia and Hb Constant Spring (CS), Hb H disease, Hb H-CS and Hb H-Quong Sze diseases, homozygous α⁰-thalassemia causing the Hb Bart’s hydrops fetalis and a remain uncharacterized α-thalassemia defect. The previously undescribed interactions of Hb Queens Park and Hb Amsterdam A1 with Hb E were detected in two fetuses with Hb Bart’s of 0.5%. The Hb Queens Park-AEBart’s disease was also noted in one pregnant woman. Prenatal analysis of the fetuses with severe fetal anemia and cardiomegaly with Hb Bart’s of 9.0% and 13.6% revealed unexpectedly the homozygous Hb CS and a compound heterozygosity of Hb CS/Hb Pakse’ with Hb E heterozygote, respectively.

Conclusions

The usefulness of detecting and differentiation of fetal α-thalassemia syndromes by quantifying of Hb Bart’s was demonstrated. Apart from the fatal condition of Hb Bart’s hydrops fetalis associated with homozygous α⁰-thalassemia, homozygous Hb CS and a compound Hb CS/Hb Pakse’ could result in severe fetal anemia and fetal complications, prenatal diagnosis is highly recommended. The simple Hb Bart’s quantification of fetal blood should prove helpful in this matter.

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.

Thalassemias: From gene to therapy

Thalassemias (α, β, γ, δ, δβ, and εγδβ) are the most common genetic disorders worldwide and constitute a heterogeneous group of hereditary diseases characterized by the deficient synthesis of one or more hemoglobin (Hb) chain(s). This leads to the accumulation of unstable non-thalassemic Hb chains, which precipitate and cause intramedullary destruction of erythroid precursors and premature lysis of red blood cells (RBC) in the peripheral blood. Non-thalassemic Hbs display high oxygen affinity and no cooperativity. Thalassemias result from many different genetic and molecular defects leading to either severe or clinically silent hematologic phenotypes. Thalassemias α and β are particularly diffused in the regions spanning from the Mediterranean basin through the Middle East, Indian subcontinent, Burma, Southeast Asia, Melanesia, and the Pacific Islands, whereas δβ-thalassemia is prevalent in some Mediterranean regions including Italy, Greece, and Turkey. Although in the world thalassemia and malaria areas overlap apparently, the RBC protection against malaria parasites is openly debated. Here, we provide an overview of the historical, geographic, genetic, structural, and molecular pathophysiological aspects of thalassemias. Moreover, attention has been paid to molecular and epigenetic pathways regulating globin gene expression and globin switching. Challenges of conventional standard treatments, including RBC transfusions and iron chelation therapy, splenectomy and hematopoietic stem cell transplantation from normal donors are reported. Finally, the progress made by rapidly evolving fields of gene therapy and gene editing strategies, already in pre-clinical and clinical evaluation, and future challenges as novel curative treatments for thalassemia are discussed.

Direct PCR assays without DNA extraction for rapid detection of hemoglobin Constant Spring and Pakse' genes: application for carrier screening and prenatal diagnosis

Hemoglobin Constant Spring (Hb CS) and Hb Pakse' (PS) are the common non-deletional α⁺-thalassemia found in Thailand. These two variants can cause severe thalassemia syndromes, especially in fetus and neonate. Molecular diagnosis is the only confirmatory method because Hb CS and Hb PS are usually missed by routine screening and Hb analysis. Therefore, we aimed to develop rapid direct PCR for the diagnosis of Hb CS and PS genes. Multiplex direct PCR assays for identifying the Hb CS and PS genes in whole blood (WB) and amniotic fluid (AF) specimens were developed. The assays were firstly validated on 290 unrelated whole blood specimens. Hb CS and PS carriers were identified in 67 (23.1%) and 6 (2.1%) cases, respectively. A 100% concordant result as compared to routine PCR assay was observed. The direct PCR assays have been applied successfully for prenatal diagnosis in two families. The result showed that the fetuses were affected by homozygous Hb CS and compound heterozygous Hb CS/Hb PS. Accurate prenatal diagnosis of these families was observed using the newly developed assays. These assays should be applicable in routine thalassemia diagnostics as well as in the large-scale screening of Hb CS and PS in the region.

Molecular basis and diagnosis of thalassemia

Thalassemia is characterized by the impaired synthesis of globin chains due to disease-causing variants in α- or β-globin genes. In this review, we provide an overview of the molecular basis underlying α- and β-thalassemia, and of the current technologies used to characterize these disease-causing variants for the diagnosis of thalassemia. Understanding these molecular basis and technologies will prove to be beneficial for the accurate diagnosis of thalassemia.