Genotype-phenotype correlations in beta-thalassemias

Does size matter? Two new deletions in the HBB gene cause β0-thalassemia

Most β-thalassemias are caused by mutations involving one or a limited number of nucleotides within the gene or its adjacent regions. They can be substitutions or deletions; in these cases, the loss ranges from a single nucleotide to even the entire HBB gene, so we wonder if the phenotype is due to the size of the deletion or the location of the mutation. To clarify this, we present two new deletions in the β-globin gene that cause β⁰-thalassemia. The hematological parameters were determined with an automated cell counter; the Hb A2 and Hb F levels were measured by performance liquid chromatography. Hemoglobins were analyzed by capillary zone electrophoresis (Sebia Capillarys Flex system) and ion-exchange HPLC (BioRad Variant II β-thalassemia Short Program). Molecular characterization was performed by automatic Sanger sequencing. The screening of common α-thalassemia point mutations and deletions in the world (21 in total) were carried out using multiplex PCR followed by reverse-hybridization with a commercial Alpha-Globin StripAssay kit. We have characterized two new mutations-(1) 1-bp deletion [CD61/62(-G)] [HBB:c.186_187delG], (2) 105-bp deletion [IVS-2-nt767-CD111] [HBB:c.316-84_333del]-and we have described, for first time in Spain, the 25-bp deletion [β nts 252 - 276 deleted] [HBB:c.93-22_95del] mutation. These mutations were classified as pathogenic by UniProt Variants confirmed according to the American College of Medical Genetics and Genomics guidelines. These mutations present a phenotype compatible with β⁰-thalassemia, supported by hematological parameters that correlate the degree of reduction in the synthesis of the β-globin chain. Identification of this type of mutation is important for genetic counselling of partners where both are carriers, so that they are aware of the genetic risk of having affected children, allowing them to take an informed decision about their reproductive choices.

Detection of the HBB: c.393T>G Mutation in Two Patients with Hypochromic Microcytic Anemia

A novel mutation, HBB: c.393T>G on the HBB gene, was detected in two hypochromic microcytic anemia patients from Yulin, in the Guangxi Province of the People's Republic of China (PRC), by next-generation sequencing (NGS). It is a nonsense mutation causing a stop codon at amino acid 131 in exon 3 of the HBB gene. It was found in a heterozygous state in two patients who both presented severe anemia during pregnancy and moderate anemia before pregnancy; Hb A₂ levels were slightly increased (more than 4.0%) in both patients. It was also detected in the father of one of the patients. This mutation was pathogenic, and caused the dominant thalassemia-like phenotypes in the two patients.

Induction of therapeutic levels of HbF in genome-edited primary β0 39-thalassaemia haematopoietic stem and progenitor cells

Hereditary persistence of fetal haemoglobin (HPFH) is the major modifier of the clinical severity of β-thalassaemia. The homozygous mutation c.-196 C>T in the Aγ-globin (HBG1) promoter, which causes Sardinian δβ⁰ -thalassaemia, is able to completely rescue the β-major thalassaemia phenotype caused by the β⁰ 39-thalassaemia mutation, ensuring high levels of fetal haemoglobin synthesis during adulthood. Here, we describe a CRISPR/Cas9 genome-editing approach, combined with the non-homologous end joining (NHEJ) pathway repair, aimed at reproducing the effects of this naturally occurring HPFH mutation in both HBG promoters. After selecting the most efficient guide RNA in K562 cells, we edited the HBG promoters in human umbilical cord blood-derived erythroid progenitor 2 cells (HUDEP-2) and in haematopoietic stem and progenitor cells (HSPCs) from β⁰ -thalassaemia patients to assess the therapeutic potential of HbF induction. Our results indicate that small deletions targeting the -196-promoter region restore high levels of fetal haemoglobin (HbF) synthesis in all cell types tested. In pools of HSPCs derived from homozygous β⁰ 39-thalassaemia patients, a 20% editing determined a parallel 20% increase of HbF compared to unedited pools. These results suggest that editing the region of HBG promoters around the -196 position has the potential to induce therapeutic levels of HbF in patients with most types of β-thalassaemia irrespective of the β-globin gene (HBB) mutations.

Association of BCL11A genetic variant (rs11886868) with severity in β-thalassaemia major & sickle cell anaemia

Background & objectives:

The amount of foetal haemoglobin that persists in adulthood affects the clinical severity of haemoglobinopathies including β-thalassaemia major and sickle cell anaemia (SCA). The present study was undertaken to analyse β-thalassaemia as well as SCA patients for the single nucleotide polymorphism (SNP), rs11886868 (T/C) in BCL11A gene and to evaluate the association between this polymorphism and severity of β-thalassaemia major and SCA.

Methods:

A total of 620 samples (420 β-thalassaemia major and 200 SCA cases) were analysed before blood transfusion using basic screening tests like complete blood analysis and osmotic fragility and further confirmed by high performance liquid chromatography (HPLC), amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and reverse dot blot techniques. All patients were transfusion dependent. Patients with β-thalassaemia and SCA were classified into mild, moderate, severe according to the severity score based on Hb levels, age of onset, age at which patients received their first blood transfusion, the degree of growth retardation and splenectomy. β-thalassaemia as well as SCA patients were analysed for the SNP, rs11886868 (T/C) in BCL11A gene and association between this polymorphism and severity of β-thalassaemia major as well as SCA was evaluated.

Results:

There was a significant difference in genotypic and allelic frequencies of BCL11A gene polymorphism between mild and moderate and mild and severe cases in both the groups. A significant (P<0.001) difference was observed in the mean HbF levels between the three genotypes in different severity groups. HbF levels were found to be high in CC genotype bearing individuals followed by TC and TT in β-thalassaemia major as well as SCA.

Interpretation & conclusions:

This study confirms that the T/C variant (rs11886868) of the BCL11A gene causing downregulation of BCL11A gene expression in adult erythroid precursors results in the induction of HbF and ameliorates the severity of β-thalassaemia as well as SCA.

Molecular Understanding of Non-Transfusion-Dependent Thalassemia Associated with Hemoglobin E-β-Thalassemia in Northeast Thailand

Non-transfusion-dependent thalassemia (NTDT) is associated with various forms of thalassemia and genetic modifiers. We report the molecular basis of NTDT in hemoglobin (Hb) E-β-thalassemia disease. This study was done in 73 adult patients encountered at the prenatal diagnosis center of Khon Kaen University, Northeast Thailand. Hematological parameters and Hb patterns were collected, and α- and β-globin gene mutations were determined. Multiple single-nucleotide polymorphisms (SNPs) including the rs7482144/Gγ-XmnI polymorphism, rs2297339, rs2838513, rs4895441, and rs9399137 in the HBS1L-MYB gene, rs4671393 and rs11886868 in the BCL11A gene, and G176AfsX179 in the KLF1 gene were examined. Five β0-thalassemia mutations and a severe β+-thalassemia mutation in trans to the βE gene were identified. No significant difference in hematological parameters was observed among β-thalassemia genotypes. Coinheritance of α-thalassemia was observed in 31 of the 73 subjects (42.5%). Four SNPs including Gγ-XmnI, rs2297339, rs4895441, and rs9399137 of HBS1L-MYB were found to be associated with high Hb F levels in 39 (53.4%) subjects. The molecular basis of NTDT in the remaining 3 (4.1%) cases could not be defined. These results indicate multiple genetic factors in NTDT patients and underline the importance of complete genotyping to provide proper management, make clinical predictions, and improve genetic counseling.

Increasing prevalence of thalassemia in America: Implications for primary care

Thalassemia, once a rarity in the United States, is increasingly encountered in clinical practice due to shifts in immigration. Early carrier screening in at-risk populations can help clinicians implement genetic counseling and prevent new cases. Chronic transfusions are the mainstay of therapy for patients with severe thalassemia (beta thalassemia major), and are used intermittently in individuals with milder forms of thalassemia (Hb H/H Constant Spring disease and beta thalassemia intermedia). Iron overload is a major source of morbidity and mortality in individuals with transfusion and non-transfusion-dependent thalassemia, necessitating iron chelation therapy. Iron overload contributes to increased risk of cirrhosis, heart failure, and endocrinopathies, while ineffective erythropoiesis and hemolysis contribute to multiple complications, including splenomegaly, extramedullary hematopoiesis, pulmonary hypertension, and thrombosis. An understanding of the importance of carrier screening, complications, monitoring, and management strategies, coupled with collaboration with a hematologist with thalassemia expertise, is essential to reduce the morbidity and mortality in patients with thalassemia.

Development and Recent Progresses of Gene Therapy for β-Thalassemia

β-thalassemias are among the most common inherited monogenic disorders worldwide due to mutations in the β-globin gene that reduce or abolish the production of the β-globin chain resulting in transfusion-dependent chronic anemia. Currently, the only curative treatment is allogeneic hematopoietic stem cells (HSCs) transplantation, but this option is limited by the a vailability of HLA-matched donor. Gene therapy, based on autologous transplantation of genetically corrected HSCs, holds the promise to treat patients lacking a compati ble bone marrow donor. I nit ial attempts of gene transfer have been unsuccessful due to limitations of available vectors to stably transfer a globin gene in HSCs and reach high and regulated expression in the erythroid progeny. With the advent of lentiviral vectors (LVs), based on human immunodeficiency virus, many of the initial limitations have been overcome. Since 2000 when Sadelain and co-workers first demonstrated successful globin gene transfer in murine thalassemia models with improvement of the phenotype using a recombinant β globin/LV, several other groups have developed different vectors encoding either β, γ or mutated globin genes and confirmed these results in both murine models and erythroid progeny derived from patient’s HSCs. In light of these encouraging results, research has recently moved into clinical trials that are ongoing or soon to begin. One participant in an ongoing gene transfer trial for β-thalassemia has achieved clinical benefit with elimination of his transfusi on re quirement. Here , dev elopmen t and recent progress of gene therapy for β-thalassemia is reviewed.

Pathophysiology and Clinical Manifestations of the β-Thalassemias

The β-thalassemia syndromes reflect deficient or absent β-globin synthesis usually owing to a mutation in the β-globin locus. The relative excess of α-globin results in the formation of insoluble aggregates leading to ineffective erythropoiesis and shortened red cell survival. A relatively high capacity for fetal hemoglobin synthesis is a major genetic modifier of disease severity, with polymorphisms in other genes also having a significant role. Iron overload secondary to enhanced absorption and red cell transfusions causes an increase in liver iron and in various other tissues, leading to endocrine and cardiac dysfunction. Modern chelation regimens are effective in removing iron and preserving or restoring organ function.

Phenotypic heterogeneity of asian Indian inversion deletions gγ(aγδβ)0 breakpoint a and breakpoint B

Asian Indian inversion deletion Gγ (Aγδβ)0-thalassemia is a rare entities characterized by high HbF. Due to interaction with various genetic factors, patients with Gγ (Aγδβ)0-thalassemia showed clinical variability. Here we are presenting the phenotypic expression of Gγ(Aγδβ)0 thalassemia under influence of various co-inherited factors. Patient with α-globin gene deletion had mild phenotype than the patient with β-globin mutations. Patient with alpha gene deletion were presenting clinical character like thalassemia intermedia while Gγ (Aγδβ)0-thalassemia patients with co- presence of beta thalssemia mutation clinically behaved like thalassemia major.

Genotype-phenotype correlation of β-thalassemia spectrum of mutations in an Indian population

Coexistence of thalassemia, hemoglobinopathies and malaria has interested geneticists over many decades. The present study represents such a population from the eastern Indian state of Orissa. Children and their siblings (n=38) were genotyped for β-thalassemia mutations and genotype-phenotype correlation was determined. The major genotype was IVS 1.5 mutation: 26% homozygous (n=10) and 37% (n=14) double heterozygous with other mutations or hemoglobinopathies. Sickle hemoglobin was the major associated hemoglobinopathy (n=12, 32%). Other mutations found were Cd 8/9, HbE and Cd 41/42. The study population did not contain any IVS 1.1 mutations which is the second major Indo-Asian genotype. Genotype-phenotype correlation revealed that genotypes of IVS 1.5, Cd 8/9 Cd 41/42 alone or in association, exhibit severe, moderate and mild severity of thalassemia, respectively. Identification of the mutation at an early age as a part of new born screening and early intervention may help reduce the thalassemia-related morbidity.

Genetic modifiers of β-thalassemia and clinical severity as assessed by age at first transfusion

BACKGROUND

The clinical and hematologic features of β-thalassemia are modulated by different factors, resulting in a wide range of clinical severity. The main factors are the type of disease-causing mutation and the ability to produce α-globin and γ-globin chains. In the present study we investigated the respective contributions of known modifiers to the prediction of the clinical severity of β-thalassemia as assessed by the patients' age at first transfusion.

DESIGN AND METHODS

We studied the effect of seven loci in a cohort of 316 Sardinian patients with β(0)-thalassemia. In addition to characterizing the β-globin gene mutations, α-globin gene defects and HBG2:g.-158C>T polymorphism, we genotyped two different markers in the BCL11A gene and three in the HBS1L-MYB intergenic region using single nucleotide polymorphism microarrays, imputation and direct genotyping. We performed Cox proportional hazard analysis of the time to first transfusion.

RESULTS

According to the resulting model, we were able to explain phenotypic severity to a large extent (Harrell's concordance index=0.72; Cox & Snell R(2)=0.394) and demonstrated that most of the model's discriminatory ability is attributable to the genetic variants affecting fetal hemoglobin production (HBG2:g.-158C>T, BCL11A and HBS1L-MYB loci: C-index=0.68, R(2)=0.272), while the remaining is due to α-globin gene defects and gender. Consequently, significantly distinct survival curves can be described in our population.

CONCLUSIONS

This detailed analysis clarifies the impact of genetic modifiers on the clinical severity of the disease, measured by time to first transfusion, by determining their relative contributions in a homogeneous cohort of β(0)-thalassemia patients. It may also support clinical decisions regarding the beginning of transfusion therapy in patients with β-thalassemia.

Molecular analysis of β-thalassemia patients: first identification of mutations HBB:c.93-2A>G and HBB:c.114G>A in Brazil

The various clinical phenotypes in β-thalassemias have stimulated the study of genetic factors that could modify the manifestations of these diseases. We examined 21 patients with β-thalassemia (β-thal) in order to identify some genetic modifying factors: β-thalassemia mutations, HBG2:g.-158C>T polymorphism, α-globin gene deletions and (AT)xNz(AT)y motif within the hypersensitive site 2-locus control region (HS2-LCR). In the 42 alleles analyzed, the most frequent mutations observed were HBB:c.92+6T>C (30.9%), HBB:c.118C>T (16.7%), HBB:c.93-21G>A (11.9%) and HBB:c.92+1G>A (4.8%); this finding is in accordance with previous data of the Brazilian population. The other genetic factors analyzed showed no relation with the severity of the disease. For the first time in Brazil, we report HBB:c.93-2A>G and HBB:c.114G>A mutations on the β-globin gene, both in a heterozygous state. This is also the first study to analyze the HS2-LCR in β-thalassemic individuals in the Brazilian population.

Recent advances in β-thalassemias

β-thalassemias are heterogeneous hereditary anemias characterized by a reduced output of β-globin chains. The disease is most frequent in the temperate regions of the world, where it represents an important health problem. In the last decades, several programs, aimed at controlling the birth rate of thalassemia newborns by screening and prenatal diagnosis of populations with high risk of β-thalassemia, have been successful accomplished. Bone marrow transplantation has offered a definitive cure for the fraction of patients with available donors. In the same time, steady improvements were made in the traditional clinical management of β-thalassemia patients. The introduction of the oral iron chelators deferiprone that preferentially chelates hearth iron and the development of novel NMR diagnostic methods has led to reduced morbility, increased survival and improved quality of life. More recently, major advances have being made in the discovery of critical modifier genes, such as Myb and especially BCL11A (B cell lymphoma 11A), a master regulator of HbF (fetal hemoglobin) and hemoglobin switching. Polimorphysms of BCL11A, Myb and γ-globin genes account for most of the variability in the clinical phenotypes in β-thalassemia and sickle cell anemia patients. Finally, the year 2010 has brought in the first successful experiment of gene therapy in a β-thalassemia patient, opening up the perspective of a generalized cure for all β- thalassemia patients.

Alpha globin gene numbers: an important modifier of HbE/beta thalassemia

HbE [beta 26 Glu-Lys] is the second most common abnormal Hb in humans. HbE when associated with beta thalassemia (HbE/beta thalassemia) in compound heterozygous state results in a clinically severe condition. HbE/beta thalassemia has a very variable clinical phenotype. One of the possible explanations for the observed variable clinical severity is variation of alpha gene number. The main aims of this study were to determine the frequency of alpha deletion/mutations and triplication in HbE/beta thalassemia patients and to study the effect of alpha gene numbers on the phenotype of these patients. 240 HbE/beta thalassemia patients who attended the Hematology Outpatient Department of the Institute were studied. Patients were divided into three groups mild (score=0-3.5), moderate (score=4-7) and severe (score=7.5-10). alpha deletion was found in 22 (7.5%), out of these 22 patients 16 (11 alphaalpha/-alpha(3.7), 4-alpha(3.7)/-alpha(3.7) & 1 alphaalpha/--(SA)) were from Gp I and 6 (alphaalpha/-alpha(3.7)) were from Gp II. alpha triplication was found in 7 (2.9%) and out of these 7 patients 5 were (alphaalpha/alphaalphaalpha(anti-3.7)) from Gp III and 2 were (alphaalpha/alphaalphaalpha(anti-3.7)) from Gp II. The most common interaction was found to be HbE/beta thalassemia and deletional alpha(+)-thalassemia (alphaalpha/-alpha(3.7)) followed by others. alpha deletions and point mutations genotype were mostly observed in the individuals from Gp I while alpha triplication was most frequent in Gp III individuals. Interaction of HbE/beta thal with alpha-thalassemia is common in the Indian population. Patients inheriting alpha deletions and point mutations behaved mildly with some exceptions, while patients with alpha triplication had a severe phenotype requiring frequent transfusions.

Amelioration of Sardinian beta0 thalassemia by genetic modifiers

Sardinian beta-thalassemia patients all are homozygotes for the same null allele in the beta-globin gene, but the clinical manifestations are extremely variable in severity. Previous studies have shown that the coinheritance of alpha-thalassemia or the presence of genetic variants that sustain fetal hemoglobin production has a strong impact on ameliorating the clinical phenotype. Here we evaluate the contribution of variants in the BCL11A, and HBS1L-MYB genes, implicated in the regulation of fetal hemoglobin, and of alpha-thalassemia coinheritance in 50 thalassemia intermedia and 75 thalassemia major patients. We confirm that alpha-thalassemia and allele C of single nucleotide polymorphism rs-11886868 in BCL11A were selectively represented in thalassemia intermedia patients. Moreover, allele G at single nucleotide polymorphism rs9389268 in the HBS1L-MYB locus was significantly more frequent in the thalassemia intermedia patients. This trio of genetic factors can account for 75% of the variation differences in phenotype severity.

The significance of the hemoglobin A(2) value in screening for hemoglobinopathies

BACKGROUND AND OBJECTIVE

The inherited hemoglobinopathies are a large group of disorders that include thalassemias and hemoglobin variants. Accurate determination of the carrier phenotype is essential for detecting couples at risk for producing offspring with hemoglobinopathy. Heterozygous beta-thalassemia is usually silent at the clinical level. His phenotype is characterized by microcytosis and hypochromia with increased hemoglobin A(2) (HbA(2)) value. Therefore, HbA(2) determination plays a key role in screening programs for hemoglobinopathy. The aim of this review is to address and suggest an approach for reducing or abolishing hemoglobinopathy screening mistakes.

DESIGN AND METHODS

Quantitative methods for HbA(2) value determination, comment on the accuracy of the test and on the interpretation of data were discussed. The most probable diagnostic conclusion based on the HbA(2) level, hemoglobin pattern, hematological parameters and iron markers was suggested in this review.

RESULTS

Hemoglobinopathies are the only genetic disease where it is possible to detect carriers using hematological findings rather than DNA analysis. However, hematological diagnosis is sometimes presumptive, and in these cases, DNA analysis becomes necessary. Complete screening is based on the detection of red cell indices, HbA(2), HbF and hemoglobin variant values. In particular, HbA(2) determination plays a key role in screening programs for beta-thalassemia because a small increase in this fraction is one of the most important markers of beta-thalassemia heterozygous carriers.

CONCLUSION

Genetic factors both related and unrelated to the beta- and alpha-globin gene clusters, iron metabolism, endocrinological disorders, and some types of anemia, together with intra- and inter-laboratory variations in HbA(2) determination, may cause difficulties in evaluating this measurement in screening programs for hemoglobinopathies. Therefore, knowledge of all these issues is important for reducing or eliminating the risk of mistakes in screening programs for hemoglobinopathies.

Can homeopathy bring additional benefits to thalassemic patients on hydroxyurea therapy? Encouraging results of a preliminary study

Several homeopathic remedies, namely, Pulsatilla Nigricans (30th potency), Ceanothus Americanus (both mother tincture and 6th potency) and Ferrum Metallicum (30th potency) selected as per similia principles were administered to 38 thalassemic patients receiving Hydroxyurea (HU) therapy for a varying period of time. Levels of serum ferritin (SF), fetal hemoglobin (HbF), hemoglobin (Hb), platelet count (PC), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), white blood cell (WBC) count, bilirubin content, alanine amino transferase (ALT), aspartate amino transferase (AST) and serum total protein content of patients were determined before and 3 months after administration of the homeopathic remedies in combination with HU to evaluate additional benefits, if any, derived by the homeopathic remedies, by comparing the data with those of 38 subjects receiving only HU therapy. Preliminary results indicated that there was a significant decrease in the SF and increase in HbF levels in the combined, treated subjects. Although the changes in other parameters were not so significant, there was a significant decrease in size of spleen in most patients with spleenomegaly and improvement in general health conditions along with an increased gap between transfusions in most patients receiving the combined homeopathic treatment. The homeopathic remedies being inexpensive and without any known side-effects seem to have great potentials in bringing additional benefits to thalassemic patients; particularly in the developing world where blood transfusions suffer from inadequate screening and fall short of the stringent safety standards followed in the developed countries. Further independent studies are encouraged.

Increased gamma-globin gene expression in beta-thalassemia intermedia patients correlates with a mutation in 3'HS1

We report a novel set of genetic markers in the DNaseI hypersensitive sites comprising the human beta-globin locus chromatin hub (CH), namely HS-111 and 3'HS1. The HS-111 (-21 G>A) and 3'HS1 (+179 C>T) transitions form CH haplotypes, which occur at different frequencies in beta-thalassemia intermedia and major patients and normal (nonthalassemic) individuals. We also show that the 3'HS1 (+179 C>T) variation results in a GATA-1 binding site and correlates with increased fetal hemoglobin production in beta-thalassemia intermedia patients. In contrast, the HS-111 (+126 G>A) transition, found in three normal chromosomes, is simply a rare polymorphism. We conclude that the CH haplotypes are useful genetic determinants for beta-thalassemia major and intermedia patients, while the 3'HS1 (+179 C>T) mutation may have functional consequences in gamma-globin genes expression.

The thalassaemia syndromes

The thalassaemia syndromes, endemic in the Mediterranean area, the Middle East, the Indian subcontinent, the Far East and in tropical Africa, are the most common hereditary disorders in humans, and millions of people are affected by diseases. Due to a widespread population flow between continents in recent past centuries, the thalassaemias are now occurring with relatively high frequency in many non-endemic areas. In the Nordic countries, homozygous thalassaemia is still relatively rare, and most health-care personnel are not familiar with these diseases. This article focuses on two important issues, namely the biological and the clinical aspects of thalassaemia.

Common alpha-thalassemia deletions in transfusion-dependent thalassemia patients in the Southeast Asia region of Myanmar

Screening of 3 common alpha-thalassemia (thal) deletions (-alpha3.7, -alpha4.2 and --SEA) in Southeast Asia was done by polymerase chain reaction in 170 unrelated Myanmar thal patients receiving transfusions. Thal deletions were detected in 27 patients (15.9%) as: (1) alpha-thal-2 (-alpha3.7/alphaalpha) in 12 heterozygous or hemoglobin (Hb) E-beta-thal cases; (2) alpha-thal-1 in 7 patients (2-alpha3.7/-alpha3.7 and 5 --SEA/alphaalpha); and (3) Hb H (-alpha3.7/--SEA) in 8 patients. The latter 15 alpha-thal-1 and Hb H patients had no beta-thal mutations and represented 8.8% of the overall patients seeking transfusion for refractory anemia in Myanmar. This is the first description of alpha-thal in Myanmar from the molecular aspect, and its clinical and racial heterogeneity are described and discussed.

Genotypic heterogeneity and correlation to intergenic haplotype within high HbF beta-thalassemia intermedia

OBJECTIVES

A molecular study was carried out of beta-thalassemia intermedia patients, compound heterozygotes for mutations usually found in beta-thalassemia major, with high levels of HbF in the absence of hereditary persistence of fetal hemoglobin (HPFH) syndrome. Our objective was to locate cis-DNA structures, DNA haplotypes, motifs, or polymorphisms that may correlate with the presence of high HbF.

METHODS

Allele-specific oligonucleotide (ASO) hybridization was used for the detection of mutations and restriction fragment length polymorphism (RFLP) analysis and automated sequencing for motifs, haplotypes, and polymorphisms. Southern blot was used for investigating alpha-thalassemia and/or alpha- or gamma-globin genes triplications. RNA extracted from burst forming unit-erythroid (BFU-e) colonies of peripheral blood mononuclear cell cultures was used in reverse transcriptase-polymerase chain reaction (RT-PCR) to investigate intergenic transcription.

RESULTS

We established that (i) the combination: T haplotype of the Agamma-delta-globin intergenic region, the motif (TA)9N10(TA)10 in the HS2 site of locus control region (LCR), and TAG pre-Ggamma haplotype is sufficient but not necessary for high HbF, (ii) the genetic determinant(s) for high HbF involves an element associated with this combination and must be present in the specific R haplotype occurring in beta-thalassemia intermedia and (iii) the genetic determinant(s) for high HbF does not involve the abolition of intergenic transcription in the Agamma-delta-globin intergenic region.

CONCLUSIONS

The genetic determinant(s) of high HbF in the absence of HPFH is linked to intergenic haplotype T and does not disrupt intergenic transcription.

Compound heterozygote state for GgammaAgamma(deltabeta) degrees -thalassemia and hereditary persistence of fetal hemoglobin

We report a hitherto undescribed interaction of a deletional (deltabeta) degrees -thalassemia and a deletional hereditary persistence of fetal hemoglobin (HPFH) in an adult Thai individual. He was a 40-year-old Thai male who had the following hematologic data: Hb 13.9 g/dL, Hct 43.8%, MCV 78.0 fL, MCH 24.7 pg, MCHC 31.6 g/dL, and RDW 17.1%. Hemoglobin analysis revealed 97% Hb F with Ggamma-globin chain predominant. Globin gene analyses demonstrated that he carried the GgammaAgamma(deltabeta) degrees -thalassemia deletion in trans to the HPFH-6. Hematologic data of the patient were compared to those of the heterozygotes for these high-Hb F determinants found in his parents and an unrelated Thai patient with a compound HPFH-6/deletion-inversion Ggamma(Agammadeltabeta) degrees -thalassemia previously described.

Regulation of the globin genes

The a- and b-globin gene clusters are subject to several levels of regulation. They are expressed exclusively in the erythroid cells, only during defined periods of development and in a perfectly tuned way, assuring, at any stage of ontogeny, a correct balance in the availability of a- and b-globin chains for hemoglobin assembling. Such a tight control is dependent on regulatory regions of DNA located either in proximity or at great distances from the globin genes in a region characterized by the presence of several DNAse I hypersensitive sites and known as the Locus Control Region. All these sequences exert stimulatory, inhibitory or more complex activities by interacting with transcription factors that bridge these regions of DNA to the RNA polymerase machinery. Many of these factors have now been cloned and the corresponding mouse genes inactivated, shading new light on the metabolic pathways they control. It is increasingly recognized that such factors are organized into hierarchies according to the number of genes and circuits they regulate. Some genes such as GATA-1 and 2 are master regulators that act on large numbers of genes at early stage of differentiation whereas others, like EKLF, stand on the lowest step and control only single or limited number of genes at late stages of differentiation. We will review recent data gathered from expression studies in cell cultures, in transgenic or K.O. murine models as well as from a clinical settings. We will also discuss the development of novel theories on the regulation of the a- and b-globin genes and clusters.

Molecular analysis of beta-thalassaemia patients in a high incidence area of southern Italy

The prevalence of eight mutations in 84 patients with beta-thalassaemia major and in 16 subjects with thalassaemia intermedia was investigated. All of the patients were Italian, originating from Eastern Sicily (Messina area) and some Calabrian regions. Genomic DNA was amplified by polymerase chain reaction (PCR). DNA molecular investigations were performed by allele-specific oligonucleotide (ASO) hybridization, to identify the following beta-thalassaemia mutations: CD39 (C-T), IVS1-110 (G-A), IVS1-6 (T-C), IVS1-1 (G-A), IVS2-745 (C-G), IVS2-1 (G-A), -87 (C-G), CD6 A (-A). Our data underline that in thalassemia intermedia two mutations were statistically prevalent: IVS1-6 T-->C (P < 0.001) and CD 6-A (P < 0.05). CD 39 was statistically prevalent in beta-thalassaemia major patients (P < 0.01). The difference between the two groups was not statistically significant for all the other mutations. Five different genotypes were recorded among thalassaemia intermedia and 15 among beta-thalassaemia major patients. Twenty-five percent of the intermedia patients and 4.5% of the major patients had homozygosity for mild mutations (group I); 62.5% of the intermedia patients and 26.2% of the major patients had combinations of mild/severe mutations (group II). In addition, homozygosity or double heterozygosity for severe mutations (group III) was found in 12.5% of the intermedia patients and 69% of the major patients. Some genotypes were restricted to thalassaemia intermedia, including heterozygosity -87/IVS1-6 and IVS1-6/CD 6-A. It is essential to understand the distribution and frequency of the relevant mutations in each population where beta-thalassaemias exist. This is of particular importance for genotype-phenotype correlation and for carrier detection, genetic counselling and prenatal diagnosis.

Clinical management of beta-thalassemia major

Management of patients with beta-thalassemia is based on adequate, safe blood transfusions (free of transfusion-transmitted diseases) and prevention of iron overload. Iron overload causes multiple endocrinopathies, contributes to osteoporosis, and is the cause of cardiac disease. Cardiac disease, secondary to iron damage, causes death in developed countries as a result of noncompliance to deferoxamine from the third decade of life. In underdeveloped countries, cardiac death starts from 12 years of age, due to nonavailability of deferoxamine. With the emergence of the advanced cardiac magnetic resonance imaging technique, early diagnosis of heart iron will allow the currently available iron-chelating agents (oral and parenteral) to be used in an innovative way to improve the quality of life and improve survival of patients with beta-thalassemia.

Effect of transfusional iron overload on immune response

Increased susceptibility to infectious disease is observed in persons with transfusion-dependent thalassemia and iron overload who experience increased exposure to pathogens and chronic immune stimulation. An abnormal low CD8(+) T (LT8) immune phenotype defines a subgroup of patients. The CD8(+) T cell immunophenotype is stable despite continued blood transfusion and is independent of age. CD8(+) T cells, but not CD4(+) T cells, were modulated during intravenous chelation with deferoxamine. Return to characteristic pretreatment levels of CD8 was observed in both the low and the normal groups, suggesting the possibility of a set point. Proliferative response to mitogens and antigens was increased by chelation. Because CD8(+) T cells are important in immune response to infectious disease, these studies suggest that intrinsic CD8(+) T cell subset differences may be a critical factor in determining susceptibility to infection independent of transfusional iron overload or alloantigen exposure.

Juxtaposed regions of extensive and minimal linkage disequilibrium in human Xq25 and Xq28

Linkage disequilibrium (LD), or the non-random association of alleles, is poorly understood in the human genome. Population genetic theory suggests that LD is determined by the age of the markers, population history, recombination rate, selection and genetic drift. Despite the uncertainties in determining the relative contributions of these factors, some groups have argued that LD is a simple function of distance between markers. Disease-gene mapping studies and a simulation study gave differing predictions on the degree of LD in isolated and general populations. In view of the discrepancies between theory and experimental observations, we constructed a high-density SNP map of the Xq25-Xq28 region and analysed the male genotypes and haplotypes across this region for LD in three populations. The populations included an outbred European sample (CEPH males) and isolated population samples from Finland and Sardinia. We found two extended regions of strong LD bracketed by regions with no evidence for LD in all three samples. Haplotype analysis showed a paucity of haplotypes in regions of strong LD. Our results suggest that, in this region of the X chromosome, LD is not a monotonic function of the distance between markers, but is more a property of the particular location in the human genome.

HbF production in beta thalassaemia heterozygotes for the IVS-II-1 G-->A beta(0)-globin mutation. Implication of the haplotype and the (G)gamma-158 C-->T mutation on the HbF level

We studied the presence of the XmnI site and the beta-globin haplotype in 24 individuals, carriers of the IVSII-1 G-->A beta(0)-globin mutation, of whom fourteen had no detectable levels of HbF, while ten coming from 5 families, presented HbF levels ranging from 1.7 to 9% of the total Hb. Of these beta-thalassaemia heterozygotes with fetal hemoglobin, 6 were females and 4 were males with median HbF levels of 4.85% and 4% respectively, and an excess of (G)gamma chains (range (G)gamma/(A)gamma: 55/45-70/30). Of the group of carriers of beta-thalassaemia with HbF < 0.1, in all cases except one, IVSII-1 mutation was found associated with XmnI polymorphic site. Haplotype analysis in these individuals revealed that in 10 cases IVSII-1 was linked with haplotype IIIb, in 1 case with haplotype IIIa, and in 3 cases with haplotype IX. On the other hand, in the group of carriers with measurable levels of HbF, IVSII-1 was always associated with haplotype IIIa and the XmnI site was either in-homozygous or the heterozygous state in-cis or in-trans with the mutated beta-globin gene. In conclusion the results of the study of these families seem that XmnI site in-cis with the IVSII-1 does not induce HbF production when this beta(0)-thalassaemia mutation is associated with IIIb or IX haplotype. On the other hand the (G)gamma -158 C-->T mutation is associated with small amounts of HbF in IVSII-1 heterozygotes, when the beta-globin mutation is linked to haplotype IIIa.

Genetic modifying factors in beta-thalassemia

The beta-thalassemia is probably the most extensively studied genetic disease. Essentially any molecular defect that has been first described in association with the globin genes has been later implicated as a molecular determinant of newly discovered genes. Accordingly, the thalassemias have always represented a model genetic disease, especially in relation to the development of programs for population screening, genetic counseling and prenatal diagnosis. Here we will review the present knowledge on the genetics of thalassemia and of the relevant modifying factors. Major categories of the carrier state, the genotypes, the clinical phenotypes and the correlation between genotype and phenotype will be discussed.

Association of unstable hemoglobin variants and heterozygous beta-thalassemia: example of a new variant Hb Acharnes or [beta53(D4) Ala --> Thr]

We report here the functional and structural characterization of Hb Acharnes [beta53(D4) Ala --> Thr], an unstable and electrophoretically silent variant, that was found associated in trans with a beta(0)-thalassemic mutation (IVSI-1 G --> A), in a patient with thalassemia intermedia syndrome. This case is discussed in comparison with other sporadic cases that we have previously investigated, resulting from the co-inheritance of a beta(0)-thalassemic mutation (CD39 C --> T) with two other types of unstable hemoglobins, Hb Köln [beta98(FG5) Val --> Met], and Hb Arta [beta45(CD4) Phe --> Cys]. It may be concluded that, in these associated forms, both the degree of instability of the variant and the altered oxygen binding properties (affecting the degree of tissue hypoxia) are major determinants of their clinical expression.

Phenotypic variability of Filipino beta(o)-thalassemia/HbE patients in Indonesia

Three Indonesian patients with identical genotypes, each compound heterozygotes for Filipino beta(o)-thalassemia/HbE, expressed different clinical severities. One patient has mild disease and is transfusion independent, while the other two are severely affected and transfusion dependent. The size of the Filipino beta(o)-globin gene deletion was confirmed to be 45 kb, resolving conflicting values given in the literature. Neither ameliorating genetic factors such as alpha-globin gene deletions or the XmnI restriction site polymorphism at position -158 upstream of the (G)gamma-globin gene, nor differences in beta-globin gene haplotype, explain the phenotypic variation. These observations have implications for the development of antenatal diagnosis in Indonesia, as at present it is not possible to give an accurate prediction of severity of phenotype for this common genotype.

Severe thalassaemia intermedia: clinical problems in the absence of hypertransfusion

In many of the parts of the world where thalassaemia is common, the blood supply is inadequate or unsafe, and desferrioxamine is too expensive for routine use. We classify some patients as having 'severe thalassaemia intermedia', i.e. those with moderately severe thalassaemia who can survive without regular transfusions, but who are at risk of many complications which are reviewed here. These include bone deformity and fractures, extramedullary haemopoietic tumours, leg ulcers, autoimmune haemolysis and, especially after splenectomy, thromboembolism and infection. An increase in the quality and safety of the blood supply, and a cheaper and/or oral iron chelator, would enable more of these patients to be treated as thalassaemia major and have improved survival and quality of life.

De novo mutation of the beta-globin gene initiation codon (ATG-->AAG) in a Northern European boy

We present a case of beta-thalassemia intermedia involving a 13-year-old boy of Northern European descent. His mother, father and older sister have normal hematologic indices. Molecular studies demonstrate that the proband carries a novel mutation of the beta-globin gene initiation codon (ATG-->AAG) which should give rise to beta(0)-thalassemia trait. The possibility of non-paternity was excluded, indicating that the novel mutation was the result of a de novo event. A review of the literature indicates that mutations involving the beta-globin gene initiation codon can give rise to a more severe phenotype than is generally associated with most other beta(+) or beta(0) mutations.

Fetal erythropoiesis and the diagnosis and treatment of hemoglobin disorders in the fetus and child

Although synthesis of adult hemoglobin (alpha 2 beta 2) is reduced or absent in both alpha and beta thalassemias, these disorders differ in their clinical significance to the fetus and neonate. alpha-Globin synthesis is observed in the yolk sac by 3 weeks of gestation and, by 9 weeks of gestation, alpha-globin represents the main alpha-like hemoglobin in the fetus. By contrast, the switch to beta-globin chain synthesis usually remains incomplete until 1 year after birth. Therefore, the clinical manifestations of homozygous beta-thalassemia may be ameliorated by sustained synthesis of fetal hemoglobin during the first 6 months of life, whereas up until 10 years ago, homozygous alpha-thalassemia was invariably associated with death in utero. More recently, reports of infants with homozygous alpha-thalassemia surviving the neonatal period have emerged, observations particularly relevant to large numbers of immigrants to North America from Southeast Asia, where alpha-thalassemia is common. Studies of patients with the beta-globin disorders thalassemia and sickle cell disease showed that the severity of both disorders is ameliorated by sustained synthesis of fetal hemoglobin into adult life. Hence, treatment for both these disorders has focused on the pharmacological manipulation of fetal hemoglobin. Studies in vitro, in animal models, and in affected patients have shown that several compounds stimulate gamma-globin synthesis and fetal hemoglobin production through a variety of proposed mechanisms. Some of the successes in human trials are outlined herein.

Relationship between the severity of beta-thalassaemia syndromes and the number of alleviating mutations

Thalassaemia intermedia, defined as homozygous beta-thalassaemia in which patients are not transfusion-dependent, covers a wide range of clinical severity. It may arise because one or more genetic factors ameliorate the otherwise severe phenotype of thalassaemia major. Exactly which and how many such mutations are necessary to produce a thalassaemia intermedia phenotype is incompletely understood, although such information would be useful both clinically and for prenatal diagnosis. We examined DNA from 28 patients with thalassaemia intermedia resident in London and 28 matched patients with thalassaemia major, for 3 types of genetic modifying factors, namely; mild beta-thalassaemia mutations, the upstream XmnI G-gamma globin gene polymorphism, and alpha-globin gene deletions. The results show that the number of alleviating mutations present has a large influence on the phenotype of patients with homozygous beta-thalassaemias. A single alleviating mutation was present in 56% of thalassaemia intermedia subjects compared with 26% of thalassaemia major subjects. Two alleviating mutations were present in 33% of thalassaemia intermedia subjects compared with 1 thalassaemia major subject. No patients with thalassaemia major had 3 alleviating mutations, in contrast to 11% of those with thalassaemia intermedia. Although the findings did not account for the full range of phenotypic variation, such information is of potential value both in the clinical management and the prenatal diagnosis of homozygous beta-thalassaemia.

Isolation, genomic structure, and expression of human erythroid Krüppel-like factor (EKLF)

Erythroid Krüppel-like factor (EKLF) is an essential transcriptional activator that directs high-level expression of the adult beta-globin promoter by binding to its CACCC element, one of a trio of highly conserved sequences present in erythroid cell-specific promoters and enhancers. This report describes the isolation and characterization of the human homolog of murine EKLF. The human EKLF transcription unit shares a number of structural properties with its marine counterpart. Human EKLF is contained within 3 kb of genomic DNA, and its coding region is interrupted by two introns whose locations are conserved with the murine gene. The three zinc fingers share >90% sequence similarity with and are predicted to bind the same target sequence as the mouse EKLF. The rest of the protein is proline-rich and retains approximately 70% sequence similarity to the mouse gene. Human EKLF is expressed in bone marrow and HEL, JK1, and OCIM1 erythroleukemic cell lines but not in K562 nor in myeloid or lymphoid cell lines. These results indicate that the genomic structure and erythroid-restricted expression of EKLF are highly conserved between the murine and human homologues. Availability of human EKLF will enable initiation of studies to molecularly assess whether it is functionally compromised in those cases of beta-thalassemia that contain a normal beta-globin gene locus.

Severity of beta-thalassemia due to genotypes involving the IVS-I-6 (T-->C) mutation

Among individuals of Mediterranean or Middle Eastern descent, the IVS-I-6 (T-->C) mutation is one of the most common causes of beta-thalassemia. In this report, we describe the clinical phenotypes of a group of beta-thalassemia patients who are compound heterozygotes for the relatively mild IVS-I-6 (T-->C) beta-thalassemia mutation and more severe beta(+)- or beta (0)-thalassemia mutations. Although most of these patients are transfusion-dependent, the requirement for regular transfusions generally occurred late in childhood. A correlation between concomitant alpha-thalassemia and a mild transfusion-independent phenotype is not apparent, indicating the involvement of other ameliorating determinants.

Extended therapy with intravenous arginine butyrate in patients with beta-hemoglobinopathies

BACKGROUND

Enhanced production of fetal hemoglobin lessens the severity of beta-thalassemia and sickle cell disease. Intravenous infusion of arginine butyrate can increase the number of reticulocytes containing fetal hemoglobin in patients with these disorders, and it has induced a substantial increase in hemoglobin in one patient with thalassemia. We therefore tested the efficacy of this agent in patients with beta-hemoglobinopathies.

METHODS

We treated 10 patients with severe beta-thalassemia or sickle cell disease with arginine butyrate at an initial dose of 500 mg per kilogram of body weight per day (final dose, 2000 mg per kilogram per day), 6 days per week, for a mean (+/- SD) of 10 +/- 1.2 weeks (range, 9 to 13). A hematologic response was defined as an increase in the hemoglobin concentration of at least 2 g per deciliter in patients with thalassemia and as a twofold increase in the fetal hemoglobin concentration in patients with sickle cell disease.

RESULTS

Increase in gamma-globin messenger RNA and in reticulocytes containing fetal hemoglobin but not in hemoglobin were observed in the patients with thalassemia. A small, unsustained increase in fetal hemoglobin was observed in two patients with sickle cell disease. Drug toxicity was minimal at standard doses. One patient had a grand mal seizure after inadvertently receiving 2000 mg of arginine butyrate per kilogram over a period of six hours.

CONCLUSIONS

Ten weeks of intravenous arginine butyrate did not produce a hematologic response in 10 patients with either severe beta-thalassemia or sickle cell disease.