Genotype-phenotype correlation and report of novel mutations in β-globin gene in thalassemia patients

Spectrum of HBB gene mutations among 696 β-thalassemia patients and carriers in Southern Vietnam

BACKGROUND

Thalassemias are common inherited blood disorders that have been extensively studied in Asia. Thus far, data on mutations of the HBB gene in Vietnamese patients with β-thalassemia are limited to small studies.

METHODS

We recruited 696 β-thalassemia patients and carriers in southern Vietnam and analyzed for the HBB gene mutations using Sanger sequencing technology.

RESULTS

We documented 27 types of known mutations and 10 types of novel variants on 737 alleles out of 1392 surveyed alleles. The three most common mutations, which account for more than ¾ of all mutant alleles, were c.79G > A (HbE), c.124_127delTTCT, and c.52A > T. The novel variants were mainly located in 5' untranslated region (c.-92delC and c.-67A > G) and 3' untranslated region (c.*4C > T, c.*116_*117insA, c.*142 T > C, c.*156G > C, c.*176_*177insA, and c.*247 T > C), except for one in intron 2 (c.316-99 T > G) and one in exon 3 (c.385delG).

CONCLUSION

We provide here a comprehensive mutation spectrum of the HBB gene in Southern Vietnam, which is crucial for carrier screening and prenatal diagnosis in the future.

Novel Therapeutic Advances in β-Thalassemia

Simple Summary

Beta-thalassemia (β-thalassemia) is an autosomal recessive inherited disorder that causes decreased production of hemoglobin. Ineffective erythropoiesis and excess iron deposition are the most significant pathophysiological problems. Chronic red blood cell transfusions along with control of iron overload are the main principles of treatment. Yet, the patients have a problematic quality of life. Recently, novel therapies have emerged based on better knowledge of the pathophysiology of the disease. Aiming at ineffective erythropoiesis through the TGF-β ligand traps, such as luspatercept, has been shown to reduce the transfusion burden. Therapeutic approaches aiming at the iron metabolism mechanisms as well as the pathway of the production of erythroid cyclic guanosine monophosphate are being used in clinical trials with encouraging results. Significant improvements in the technique of hemopoietic stem cell transplantation have been accomplished, with a focus on the improvement of the conditioning regimen and the donor selection. Gene therapy has exhibited remarkable advances using lentiviral β-globin gene insertion techniques or gene editing platforms that target the suppression of γ-globin repressors. All these approaches will have a positive result in the quality of life of thalassemia patients.

Abstract

The main characteristic of the pathophysiology of β-thalassemia is reduced β-globin chain production. The inevitable imbalance in the α/β-globin ratio and α-globin accumulation lead to oxidative stress in the erythroid lineage, apoptosis, and ineffective erythropoiesis. The result is compensatory hematopoietic expansion and impaired hepcidin production that causes increased intestinal iron absorption and progressive iron overload. Chronic hemolysis and red blood cell transfusions also contribute to iron tissue deposition. A better understanding of the underlying mechanisms led to the detection of new curative or “disease-modifying” therapeutic options. Substantial evolvement has been made in allogeneic hematopoietic stem cell transplantation with current clinical trials investigating new condition regimens as well as different donors and stem cell source options. Gene therapy has also moved forward, and phase 2 clinical trials with the use of β-globin insertion techniques have recently been successfully completed leading to approval for use in transfusion-dependent patients. Genetic and epigenetic manipulation of the γ- or β-globin gene have entered the clinical trial setting. Agents such as TGF-β ligand traps and pyruvate kinase activators, which reduce the ineffective erythropoiesis, have been tested in clinical trials with favorable results. One TGF-β ligand trap, luspatercept, has been approved for use in adults with transfusion-dependent β-thalassemia. The induction of HbF with the phosphodiesterase 9 inhibitor IMR-687, which increase cyclic guanosine monophosphate, is currently being tested. Another therapeutic approach is to target the dysregulation of iron homeostasis, using, for example, hepcidin agonists (inhibitors of TMPRSS6 and minihepcidins) or ferroportin inhibitors (VIT-2763). This review provides an update on the novel therapeutic options that are presently in development at the clinical level in β-thalassemia.

A novel β-thalassemia variant at HBB:c.14delC (Codon 4, -C) identified via next-generation sequencing

OBJECTIVES

β-Thalassemia (β-thal) is a genetic disease of the blood caused by mutations in the β-globin gene. Conventional methods for detecting thalassemia variants often miss rare and novel variants. Identifying the rare and novel β-thal variants, especially in the high prevalence regions, would enable better disease prevention.

METHODS

A Chinese family who had joined the Thalassemia Prevention Program was recruited in this study. The β-thal carrier screening was performed using next-generation sequencing (NGS), and the results were validated through direct DNA sequencing. Hematological parameters were analyzed, and hemoglobin electrophoresis was performed. Additionally, the presence of thalassemia-associated deletions was determined using gap-polymerase chain reaction.

RESULTS

A novel frameshift variant of β-thal, HBB:c.14delC(Codon 4, -C), was identified in a 31-year-old Chinese man. Subsequent genetic investigation showed that his mother also carried this novel variant. Hematological analysis and clinical evaluation suggested that this variant was present in the heterozygous state and might belong to a severe phenotype of β-thal.

CONCLUSIONS

We identified a novel frameshift variant of β-thal. NGS has the potential for identifying rare and novel thalassemia variants and broadening the spectrum of thalassemia screening and thus may contribute to effective prevention of thalassemia.

HBB mutations and HbA2 level: Escaping the carrier screening programs

HbA2 level alone for beta thalassemia trait may not be accurate and reliable even without iron deficiency so molecular genetic testing is important and should be considered for some individuals.

The phenotypic and molecular diversity of hemoglobinopathies in India: A review of 15 years at a referral center

INTRODUCTION

The hemoglobinopathies pose a significant health burden in India. Apart from the β thalassemias and sickle cell disorders, α thalassemias and structural hemoglobin variants are also common. Here we have reviewed the phenotypic and molecular diversity of hemoglobinopathies encountered at a referral center in western India over a period of 15 years.

MATERIALS AND METHODS

Screening for hemoglobinopathies was done using HPLC and cellulose acetate electrophoresis. Molecular characterization was done using Covalent Reverse Dot Blot Hybridization (CRDB), Amplification Refractory Mutation System (ARMS), GAP PCR and direct DNA sequencing.

RESULTS

The study includes 31 075 individuals who were referred for diagnosis of hemoglobinopathies and prenatal diagnosis. Of these 14 423 individuals showed various hemoglobin abnormalities. Beta genotyping in 5615 individuals showed the presence of 49 β thalassemia mutations. 143 β thalassemia heterozygotes had normal or borderline HbA₂ levels. We identified three δ gene mutations (HbA₂ Pellendri, HbA₂ St.George, HbA₂ Saurashtra) in β thalassemia heterozygotes leading to normal HbA₂ levels. The commonest defects among the raised Hb F determinants were Gγ(Αγδβ)⁰ Indian inversion and the HPFH-3 Indian deletion. A total of 312 individuals showed the presence of α thalassemia, of which 12.0% had a single α gene deletion (-α/αα). HbH disease was identified in 29 cases with 10 different genotypes. Alpha globin gene triplication was seen in 2.1% of β thalassemia heterozygotes with a thalassemia intermedia phenotype. Seven unusual α chain variants and eight uncommon β chain variants were identified.

CONCLUSION

The repertoire of molecular defects seen in the different globin genes will be valuable for management and control of these disorders both in India as well as in other countries where there is a huge influx of migrant populations from India.

A Novel -72 (T→A) β-Promoter Mutation Causing Slightly Elevated HbA2 in a Vietnamese Heterozygote

We report a novel β⁺-thalassemia mutation found in a Vietnamese family. The molecular defect T→A lies at -72 of the β-globin gene promoter, within the conserved CCAAT box. The index case was a 5-year-old child having red blood cells indices close to normal and slightly increased level of HbA₂ (3.96%). The expression of the mutated β allele was inferred by luciferase reporter assay in K562 cells. The β -72 determinant is the eighth β-thalassemic mutation identified in Vietnam and it was not previously reported in any population. The absence of homozygous or compound heterozygous states did not allow us to precisely predict either its clinical impact or its relevance in management programs. Our results further underline the importance of identifying and characterizing new or rare β⁺-thalassemic alleles in carrier screening and prenatal diagnosis.

Molecular Characterization of β-Thalassemia Intermedia in Southeast Iran

Inheritance of mild mutations within the β-globin gene and coinheritance of α-thalassemia (α-thal) are known as two important genetic modifiers in β-thalassemia (β-thal) intermedia (β-TI). We aimed to evaluate the spectrum of β- and α-thal mutations in β-TI patients in Southeast Iran. Common β- and α-globin gene mutations were detected by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and multiplex gap-PCR, respectively. There were 26 male (57.8%) and 19 female (42.2%) patients. HBB: c.92 + 5T > C [IVS-I-5 (G > C)] and HBB: c.-138C + 1G > A [IVS-II-I (G > A)] represented the prevalent alleles with respective frequencies of 60.0 and 10.0%. Other β-globin mutations included HBB: c.-138C > T [-88 (C > T)], HBB: c.27_28insG [frameshift codons (FSC) 8/9 (+G)], HBB: c.46delT [codon 15 (-T)], HBB: c.93-22_95del (IVS-I, 25 del), and the 619 bp deletion (NG_000007.3: g.71609_72227del619). The predominant genotypic combinations were β(0)/β(0) (68.9%), β(0)/β(+ )(8.9%) and β(+)/β(+ )(2.2%). Coinheritance of α-thal was observed in 33.0% of the patients, with the -α(3.7) (rightward) (NG_000006.1: g.34164_37967del3804) as the most common deletion (86.0%). One patient was diagnosed with the -α(4.2) (leftward) (AF221717) and one with the - -(MED) (g.24664_41064del16401) deletions, while no patients carried the -(α)(20.5) (g.15164_37864del22701), α(-5 nt) (HBA2: c.95 + 2_95_6delTGAGG) or codon 19 (-G) (HBA2: c.56delG) mutations. The alleviating molecular mechanism was not explainable by β(+ )or concurrent α-thal in more than half of our β-TI patients. This encourages conducting more studies to identify other contributing factors, especially Hb F-inducing genetic modifiers.

2017 Clinical trials update in new treatments of β-thalassemia

The underlying basis of β-thalassemia pathology is the diminished β-globin synthesis leading to α-globin accumulation and premature apoptotic destruction of erythroblasts, causing oxidative stress-induced ineffective erythropoiesis, bone marrow hyperplasia, splenomegaly, and increased intestinal iron absorption with progressive iron overload. Better understanding of the molecular mechanisms underlying this disease led to the recognition of new targets with potential therapeutic utility. Agents such as JAK2 inhibitors and TGF-β ligand traps that reduce the ineffective erythropoiesis process are already being tested in clinical trials with promising results. Other agents that aim to reduce oxidative stress (activators of Foxo3, HRI-eIF2aP, Prx2, Hsp70, and PK anti-oxidant systems and inhibitors of HO-1) and to decrease iron overload (hepcidin agonists, erythroferrone inhibitors and exogenous transferrin) are also under experimental investigation. Significant progress has also been made in the area of allogeneic hematopoietic stem cell transplantation with several ongoing clinical trials examining new condition regimens as well as different donor selection and stem cell source options. Gene therapy has reached a critical point and phase 1 clinical trials have recently been launched to examine the effectiveness and especially long term safety. Epigenetic manipulation and genomic editing of the γ- or β-globin gene are novel and promising experimental gene therapy approaches for β-thalassemia giving hope for cure for this chronic disease. This review outlines the key points of the molecular mechanisms underlying β-thalassemia in relation to the development of new therapies and an update is given both at the pre-clinical and clinical level. Am. J. Hematol. 91:1135-1145, 2016. © 2016 Wiley Periodicals, Inc.