Alpha-thalassaemia

Molecular and cellular analysis of a novel HBA2 mutation (HBA2: c.94A > G) shows activation of a cryptic splice site and generation of a premature termination codon

In this study, we describe the clinical features and provide experimental analyses of a novel point mutation affecting the penultimate nucleotide of the first exon of the HBA2 (HBA2: c.94A > G) gene identified in a 26-year-old female who also carries a heterozygous Hb E (HBB: c.79G > A) variant. The aim of the study was to investigate the impact of this point mutation on the transcriptional activity of the HBA2 gene using a combination of an initial in silico prediction followed by in vitro mutagenesis and transcriptional activity assessment. The analyses revealed that the HBA2: c.94A > G point mutation causes the activation of a cryptic splice site located 49 bp upstream of the exon1-intron1 boundary in both HBA2 long and short isoforms, thus generating a frameshift and a premature termination codon between codons 48 and 49 in the second exon. A rapid degradation of the aberrantly spliced transcripts by the nonsense mediated decay (NMD) surveillance system is highly indicative of an α-thalassemia (α-thal) phenotype. However, the abnormal mRNA may not be entirely degraded since the proband presents a slight splenomegaly that could be the sign of extra vascular hemolysis.

Deferasirox for the treatment of iron overload in non-transfusion-dependent thalassemia

Non-transfusion-dependent thalassemia (NTDT) defines a group of patients who do not require regular transfusions for survival, but are at significant risk of iron accumulation from underlying disease-related mechanisms distinct from transfusional iron overload. Management of iron overload in NTDT has received little attention compared with that of β-thalassemia major, despite evidence of significant iron-induced complications with advancing age. The efficacy and safety of the iron chelator deferasirox in NTDT has been evaluated in two pilot studies and the first prospective, randomized, placebo-controlled study (THALASSA) of any chelator in NTDT. Treatment with deferasirox for up to 2 years yielded a sustained reduction in iron burden, with a clinically manageable safety profile. Following these trial data, deferasirox is the first iron chelator approved for use in NTDT patients, and with NTDT guidelines now available, physicians are better equipped to achieve effective monitoring and management of iron burden in NTDT.

Detection of three common α-thalassemia in non-deletion types and six common thalassemia in deletion types by QF-PCR

OBJECTIVE

Thalassemia is one of the most common monogenic hereditary diseases in tropical and subtropical regions. An effective way to avoid the birth of severe thalassemia patients is to strengthen the thalassemia screening of couples before wives are pregnant. Thalassemia gene carriers can be diagnosed by molecular biology in order to conduct effective guidance for fertility.

DESIGNS AND METHODS

For --(SEA) and --(THAI) of α-thalassemia and HPFH-SEA and DBT of β-thalassemia, we design the fGap-PCR primer; for α(CS)α, α(QS)α and α(WS)α, we design the fAS-PCR primer; for -α(3.7)and -α(4.2), we design the QF-PCR primer; and lastly, we use universal primers and multiple-tailed primers to make a single-tube QF-PCR system.

RESULTS

When the QF-PCR system is used to diagnose 123 screening samples of thalassemia genotyping, the typing result is consistent with conventional diagnosis of Gap-PCR and PCR-RDB.

CONCLUSIONS

Compared with conventional Gap-PCR and PCR-RDB, this QF-PCR system is easy to operate, has high precision, and can diagnose genotypes in a large scale. Its automatic operation is more suitable for the large-scale screening of the thalassemia gene.

Distribution of alpha thalassaemia gene variants in diverse ethnic populations in malaysia: data from the institute for medical research

Alpha thalassaemia is highly prevalent in the plural society of Malaysia and is a public health problem. Haematological and molecular data from 5016 unrelated patients referred from various hospitals to the Institute for Medical Research for α thalassaemia screening from 2007 to 2010 were retrieved. The aims of this retrospective analysis were to describe the distribution of various alpha thalassaemia alleles in different ethnic groups, along with their genotypic interactions, and to illustrate the haematological changes associated with each phenotype. Amongst the patients, 51.2% (n = 2567) were diagnosed with α thalassaemia. Of the 13 α thalassaemia determinants screened, eight different deletions and mutations were demonstrated: three double gene deletions, --(SEA), --(THAI), --(FIL); two single-gene deletions, α-³·⁷ and -α⁴·²; and three non-deletion mutations, Cd59G > A (haemoglobin [Hb] Adana), Cd125T > C (Hb Quong Sze) and Cd142 (Hb Constant Spring). A high incidence of α-³·⁷ deletion was observed in Malays, Indians, Sabahans, Sarawakians and Orang Asli people. However, the --SEA deletion was the most common cause of alpha thalassaemia in Chinese, followed by the α-³·⁷ deletion. As many as 27 genotypic interactions showed 1023 α thalassaemia silent carriers, 196 homozygous α⁺ thalassaemia traits, 973 heterozygous α⁰ thalassaemia carriers and 375 patients with Hb H disease. Statistical analysis showed a significant difference in the distribution of α thalassaemia determinants amongst the various ethnic groups. Hence, the heterogeneous distribution of common determinants indicated that the introduction of an ethnicity-targeted hierarchical α thalassaemia screening approach in this multi-ethnic Malaysian population would be effective.

A systematic review of factors associated with the deferral of donors failing to meet low haemoglobin thresholds

BACKGROUND/OBJECTIVES

Blood donors attending a donation session may be deemed ineligible to donate blood due to a failure to meet low haemoglobin (Hb) thresholds. Several studies have identified factors associated with a donor falling below these Hb thresholds. A review of these factors will inform future prospective studies and form the basis for predictive models of deferral due to low Hb.

MATERIALS/METHODS

Studies were identified by searching MEDLINE, EMBASE, The Cochrane Library and the WHO International Clinical Trials Registry from 1980 to September 2012. Demographic data, donor history, haematological/biological factors and the primary outcome of deferral due to low Hb were extracted. Analyses were descriptive and quantitative; pooled odds ratios (ORs) were obtained by meta-analysis.

RESULTS

Fifty-five studies met the inclusion criteria. A consistently higher rate of low Hb deferral was reported in females compared with males; meta-analysis showed a significantly greater risk of deferral due to low Hb in females compared with males in studies with universal Hb thresholds for males and females (OR 14.91, 95% confidence interval (CI) 12.82-17.34) and in studies with sex-specific Hb thresholds (OR 8.19, 95% CI 4.88-13.74). Greater rates of deferral due to low Hb were also associated with increasing age, higher ambient temperature, low body weight, shorter inter-donation interval and in donors of Hispanic or African descent.

CONCLUSION

This work will help to define the criteria that should be considered in any large scale study of blood donor deferral, especially those that measure or aim to change failure to meet low Hb thresholds.

Molecular epidemiological survey of hemoglobinopathies in the Wuxi region of Jiangsu Province, eastern China

In order to determine the prevalence and molecular characterization of hemoglobinopathies in the Wuxi region of Jiangsu Province in the People's Republic of China (PRC), a total of 10,297 healthy people selected from a regional hospital were screened. Hemoglobin (Hb) electrophoresis, complete blood cell (CBC) count, polymerase chain reaction (PCR), DNA sequencing, reverse dot-blot and multiplex ligation-dependent probe amplification (MLPA) were used to detect Hb variants, thalassemias and hereditary persistence of fetal Hb (HPFH). Two thousand and twenty-one adult subjects were screened for thalassemia, five cases were identified as α-thalassemia (α-thal) carriers including three cases of the -α(3.7) (rightward) deletion, one case of the - -(SEA) deletion and one case of β-thal [IVS-II-654 (C>T), (HBB: c.316-197C>T)]. The incidence of Hb variants, thalassemia and HPFH/δβ-thal were 0.136% (14/10,297), 0.25% (5/2021) and 0.0001% (1/10,297), respectively. Eight genotypes of Hb variants were found, including Hb E [β26(B8)Glu→Lys, GAG>AAG; HBB: c.79G>A], Hb J-Bangkok [β56(D7)Gly→Asp (GGC>GAC); HBB; c.170G>A], Hb G-Coushatta [β22(4)Glu→Ala (GAA>GCA); HBB: c.68A>C], Hb Queens [α34(B15)Leu→Arg (CTG>CGG) (α2 or α1); HBA2: c.104T>G (or HBA1)], Hb I [α16(A14)Lys→Glu, AAG>GAG (α1); HBA1: c.49A>G], Hb Beijing [α16(A14)Lys→Asn (AAG>AAC or AAT) (α2 or α1); HBA2: c.51G>C (or HBA1) or 51G>T (or HBA1)], Hb Ube-2 [α68(E17)Asn→Asp (AAC>GAC) (α2 or α1); HBA2: c.205A>G (or HBA1)] and Hb G-Taipei [β22(B4)Glu→Gly (GAA>GGA); HBB: c.68A>G]. A Sicilian δβ(0)-thal, identified for the first time in Asia, was also found in this survey.

A stepwise α-thalassemia screening strategy in high-prevalence areas

INTRODUCTION

Coinheritance of α-thalassemia influences the clinical and hematological phenotypes of β-hemoglobinopathies (β-thalassemia and sickle cell disease) and when present together in significant frequency within a population, a spectrum of clinical forms is observed. Precise molecular characterization of α-thalassemia is important in understanding their disease-modifying role in β-hemoglobinopathies and for diagnostic purposes.

PATIENTS AND METHODS

Because currently used approaches are labor/cost-intensive, time-consuming, error-prone in certain genotype combinations and not applicable for large epidemiological screening, we developed a systematic stepwise strategy to overcome these difficulties. We successfully applied this to characterize the α-globin gene status in 150 Omani cord blood samples with Hb Barts and 32 patients with HbH disease.

RESULTS

We observed a good correlation between α-globin genotypes and level of Hb Bart's with the Hb Bart's levels significantly higher in both deletional and non-deletional α-globin genotypes. The most common α-globin genotype in HbH cases was α(TSaudi) α/α(TSaudi) α (n = 16; 50%) followed by -α(3.7) /-(MED) (n = 10; 31%). This approach detects also the α-globin gene triplication as exemplified by the study of a family where the β-globin gene defect failed to explain the β-thalassemia intermedia phenotype.

CONCLUSION

Molecular characterization of α-thalassemia is complex due to high sequence homology between the duplicated α-globin genes and to the existence of a variety of gene rearrangements (small and large deletions of various sizes) and punctual substitutions (non-deletional alleles). The novelty of our strategy resides, not in the individual technical steps per se but in the reasoned sequential order of their use taking into consideration the hematological phenotype as well.

Deferasirox demonstrates a dose-dependent reduction in liver iron concentration and consistent efficacy across subgroups of non-transfusion-dependent thalassemia patients

The 1-year THALASSA study enrolled 166 patients with various non-transfusion-dependent thalassemia (NTDT) syndromes, degrees of iron burden and patient characteristics, and demonstrated the overall efficacy and safety of deferasirox in reducing liver iron concentration (LIC) in these patients. Here, reduction in LIC with deferasirox 5 and 10 mg/kg/day starting dose groups is shown to be consistent across the following patient subgroups—baseline LIC/serum ferritin, age, gender, race, splenectomy (yes/no), and underlying NTDT syndrome (β-thalassemia intermedia, HbE/β-thalassemia or α-thalassemia). These analyses also evaluated deferasirox dosing strategies for patients with NTDT. Greater reductions in LIC were achieved in patients dose-escalated at Week 24 from deferasirox 10 mg/kg/day starting dose to 20 mg/kg/day. Patients who received an average actual dose of deferasirox >12.5–≤17.5 mg/kg/day achieved a greater LIC decrease compared with the ≥7.5–≤12.5 mg/kg/day and >0–<7.5 mg/kg/day subgroups, demonstrating a dose–response efficacy. LIC reduction across patient subgroups was generally consistent with the primary efficacy analysis with a similar safety profile. Am. J. Hematol. 88:503–506, 2013. © 2013 Wiley Periodicals, Inc.

Treating iron overload in patients with non-transfusion-dependent thalassemia

Despite receiving no or only occasional blood transfusions, patients with non-transfusion-dependent thalassemia (NTDT) have increased intestinal iron absorption and can accumulate iron to levels comparable with transfusion-dependent patients. This iron accumulation occurs more slowly in NTDT patients compared to transfusion-dependent thalassemia patients, and complications do not arise until later in life. It remains crucial for these patients' health to monitor and appropriately treat their iron burden. Based on recent data, including a randomized clinical trial on iron chelation in NTDT, a simple iron chelation treatment algorithm is presented to assist physicians with monitoring iron burden and initiating chelation therapy in this group of patients. Am. J. Hematol. 88:409–415, 2013. © 2013 Wiley Periodicals, Inc.

Prenatal diagnosis of haemoglobinopathies: our experience of 523 cases

BACKGROUND

We performed counselling for prenatal diagnosis (PD) of haemoglobinopathies in 372 couples. Thirty-four out of 372 (9.1%) did not undergo PD: six due to spontaneous abortion; nine because it was too difficult to make a decision if PD was positive; 18 because counselling excluded the carrier status of one or both parents; and one because parental mutations were mild.

METHODS

Eleven out of 338 (3.3%) couples underwent PD because they had a thalassaemic child; 106 (31.4%) were found to be at high risk during pre-conceptional screening; 221 (65.4%) because of familiarity. Of 523 PDs in 486 (92.9%), including six dichorionic twin pregnancies, PD was performed on DNA from chorionic villi (CV), and in 37 from amniocytes (7.1%). In 1/523 cases, PD was not completed because DNA from CV was not sufficient; in two cases single tandem repeat analysis revealed maternal contamination of foetal DNA; in 7/522 (1.3%) cases PD revealed non-paternity. In 435/522 (83.3%) cases, PD was performed using reverse dot-blot and ARMS; 34/522 (6.5%) required sequencing. In 53/522 (10.2%) cases it was necessary to test globin loci for large rearrangements.

RESULTS

One hundred and twenty out of 522 (23.0%) PDs revealed an affected foetus. In all but two cases the couple interrupted pregnancy. In the six twin pregnancies PD revealed a normal and a carrier foetus (two cases), carrier status in both foetuses (two cases) and a carrier and an affected foetus (two cases). In these latter cases the couple planned selective interruption.

CONCLUSIONS

Our PD procedure is successful and reliable, and is useful in high-risk areas characterised by molecular heterogeneity.

Hemoglobin A2 Lowered by Iron Deficiency and α -Thalassemia: Should Screening Recommendation for β -Thalassemia Change?

Screening for β-thalassemia trait (BTT) relies on measuring hemoglobin (Hb) A₂. Since multiple factors can affect HbA₂ levels, the screening can become unreliable. In 1356 healthy Arabs enrolled into a federally funded premarital BTT screening program, the effects of iron deficiency (ID), α⁺-thalassemia trait, gender, smoking, and tribalism on HbA₂ were studied. The complete blood count and hemoglobin fractions were determined on the entire cohort; serum ferritin (<15 μg/L) in 391 subjects was used to determine ID. BTT was present in 29 (2.1%) subjects (HbA₂ > 3.5%). Among 77(20.3%) subjects with ID, the mean HbA₂ (2.30 ± 0.23%) was 0.2% lower than in subjects without iron deficiency (2.50 ± 0.24%, P < 0.0001). In 65 (38%)/172 subjects with phenotypic α⁺-thalassemia trait, the mean HbA₂ (2.43 ± 0.24%) was 0.13% lower than in subjects without α⁺-thalassemia trait, P < 0.0001. The mean HbA₂ did not differ between males and females, smokers and nonsmokers, and between the tribes. Thus, 35 (2.6%) subjects with HbA₂ between 3.2 and 3.5% were at a risk of false negative diagnosis of BTT. Since iron deficiency and α⁺-thalassemia are both common and both lower HbA₂, modifications in screening recommendations for BTT are proposed.

Evidence of recent natural selection on the Southeast Asian deletion (--(SEA)) causing α-thalassemia in South China

Background

The Southeast Asian deletion (--^SEA) is the most commonly observed mutation among diverse α-thalassemia alleles in Southeast Asia and South China. It is generally argued that mutation --^SEA, like other variants causing hemoglobin disorders, is associated with protection against malaria that is endemic in these regions. However, little evidence has been provided to support this claim.

Results

We first examined the genetic imprint of recent positive selection on the --^SEA allele and flanking sequences in the human α-globin cluster, covering a genomic region spanning ~410 kb, by genotyping 28 SNPs in a Chinese population consisting of 76 --^SEA heterozygotes and 138 normal individuals. The pattern of linkage disequilibrium (LD) and the long-range haplotype test revealed a signature of positive selection. The network of inferred haplotypes suggested a single origin of the --^SEA allele.

Conclusions

Thus, our data support the hypothesis that the --^SEA allele has been subjected to recent balancing selection, triggered by malaria.

Hemoglobinopathy: molecular epidemiological characteristics and health effects on Hakka people in the Meizhou region, southern China

Background

Hemoglobinopathies are the most common inherited diseases in southern China. However, there have been only a few epidemiological studies of hemoglobinopathies in Guangdong province.

Materials and Methods

Peripheral blood samples were collected from 15299 “healthy” unrelated subjects of dominantly ethnic Hakka in the Meizhou region, on which hemoglobin electrophoresis and routine blood tests were performed. Suspected cases with hemoglobin variants and hereditary persistence of fetal hemoglobin (HPFH) were further characterized by PCR, DNA sequencing, reverse dot blot (RDB) or multiplex ligation-dependent probe amplification (MLPA). In addition, 1743 samples were randomly selected from the 15299 subjects for thalassemia screening, and suspected thalassemia carriers were identified by PCR and RDB.

Results

The gene frequency of hemoglobin variants was 0.477% (73/15299). The five main subgroups of the ten hemoglobin variants were Hb E, Hb G-Chinese, Hb Q-Tahiland, Hb New York and Hb J-Bangkok. 277 cases (15.89%, 277/1743) of suspected thalassemia carriers with microcytosis (MCV<82 fl) were found by thalassemia screening, and were tested by a RDB gene chip to reveal a total of 196 mutant chromosomes: including 124 α-thalassemia mutant chromosomes and 72 β-thalassemia mutant chromosomes. These results give a heterozygote frequency of 11.24% for common α and β thalassemia in the Hakka population in the Meizhou region. 3 cases of HPFH/δβ-thalassemia were found, including 2 cases of Vietnamese HPFH (FPFH-7) and a rare Belgian ^Gγ(^Aγδβ)⁰–thalassemia identified in Chinese.

Conclusions

Our results provide a detailed prevalence and molecular characterization of hemoglobinopathies in Hakka people of the Meizhou region. The estimated numbers of pregnancies each year in the Meizhou region, in which the fetus would be at risk for β thalassemia major or intermedia, Bart’s hydrops fetalis, and Hb H disease, are 25 (95% CI, 15 to 38), 40 (95% CI, 26 to 57), and 15 (95% CI, 8 to 23), respectively.

The potential role of cell penetrating peptides in the intracellular delivery of proteins for therapy of erythroid related disorders

The erythroid related disorders (ERDs) represent a large group of hematological diseases, which in most cases are attributed either to the deficiency or malfunction of biosynthetic enzymes or oxygen transport proteins. Current treatments for these disorders include histo-compatible erythrocyte transfusions or allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy delivered via suitable viral vectors or genetically modified HSCs have been under way. Protein Transduction Domain (PTD) technology has allowed the production and intracellular delivery of recombinant therapeutic proteins, bearing Cell Penetrating Peptides (CPPs), into a variety of mammalian cells. Remarkable progress in the field of protein transduction leads to the development of novel protein therapeutics (CPP-mediated PTs) for the treatment of monogenetic and/or metabolic disorders. The “concept” developed in this paper is the intracellular protein delivery made possible via the PTD technology as a novel therapeutic intervention for treatment of ERDs. This can be achieved via four stages including: (i) the production of genetically engineered human CPP-mediated PT of interest, since the corresponding native protein either is missing or is mutated in the erythroid progenitor cell (ErPCs) or mature erythrocytes of patients; (ii) isolation of target cells from the peripheral blood of the selected patients; (iii) ex vivo transduction of cells with the CPP-mediated PT of interest; and (iv) re-administration of the successfully transduced cells back into the same patients.

Protein antioxidants in thalassemia

It is common knowledge that thalassemic patients are under significant oxidative stress. Chronic hemolysis, frequent blood transfusion, and increased intestinal absorption of iron are the main factors that result in iron overload with its subsequent pathophysiologic complications. Iron overload frequently associates with the generation of redox-reactive labile iron, which in turn promotes the production of other reactive oxygen species (ROS). If not neutralized, uncontrolled production of ROS often leads to damage of various intra- and extracellular components such as DNA, proteins, lipids, and small antioxidant molecules among others. A number of endogenous and exogenous defense mechanisms can neutralize and counteract the damaging effects of labile iron and the reactive substances associated with it. Endogenous antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and ferroxidase, may directly or sequentially terminate the activities of ROS. Nonenzymatic endogenous defense mechanisms include metal binding proteins (ceruloplasmin, haptoglobin, albumin, and others) and endogenously produced free radical scavengers (glutathione (GSH), ubiquinols, and uric acid). Exogenous agents that are known to function as antioxidants (vitamins C and E, selenium, and zinc) are mostly diet-derived. In this review, we explore recent findings related to various antioxidative mechanisms operative in thalassemic patients with special emphasis on protein antioxidants.

The molecular basis of α-thalassemia

The globin gene disorders including the thalassemias are among the most common human genetic diseases with more than 300,000 severely affected individuals born throughout the world every year. Because of the easy accessibility of purified, highly specialized, mature erythroid cells from peripheral blood, the hemoglobinopathies were among the first tractable human molecular diseases. From the 1970s onward, the analysis of the large repertoire of mutations underlying these conditions has elucidated many of the principles by which mutations occur and cause human genetic diseases. This work will summarize our current knowledge of the α-thalassemias, illustrating how detailed analysis of this group of diseases has contributed to our understanding of the general molecular mechanisms underlying many orphan and common diseases.

Epidemiological profile of common haemoglobinopathies in Arab countries

Haemoglobinopathies including the thalassemias and sickle cell disease are known to be prevalent inherited disorders in most Arab countries with varying prevalence rates and molecular characterisation. β-thalassemia is encountered in polymorphic frequencies in almost all Arab countries with carrier rates of 1-11 % and a varying number of mutations. The most widespread mutation in Lebanon, Egypt, Syria, Jordan, Tunisia and Algeria is the IVS-I-110 (G>A). In the Eastern Arabian Peninsula, the Asian Indian mutations (IVS-I-5 (G>C), codons 8/9 (+G) and IVS-I (-25 bp del)) are more common. The α-thalassemias are encountered in the majority of Arab countries in frequencies ranging from 1 to 58 % with the highest frequencies reported from Gulf countries. The (-α(3.7)) mutation is the most frequent followed by the non-deletional α2 polyadenylation signal mutation (AATAAA>AATAAG) and the α2 IVS1 5-bp deletion. The rates of sickle cell trait in Arab countries range from 0.3 to 30 %, with the Benin, the Arab-Indian and the Bantu haplotypes constituting the bulk of the haplotypes, leading to two major phenotypes; a mild one associated with the Arab-Indian and a severe one with the Benin and Bantu haplotypes. Public health approaches targeting prevention of haemoglobinopathies in Arab countries include newborn screening for sickle cell disease, and premarital screening for carriers of β-thalassemia and sickle cell disease. These services are still patchy and inadequate in many Arab countries recommending the upgrade of these services with strengthening of the education and training of health care providers and raising public awareness on the feasibility of prevention and care for haemoglobinopathies.

The spectrum of α-thalassemia mutations in the Kurdish population of Northeastern Iraq

In an attempt to determine the spectrum of α-thalassemia (α-thal) mutations in the Kurdish population of Northeastern (NE) Iraq, a total of 101 unrelated adults with unexplained hypochromia and/or microcytosis were enrolled. α-Thalasssemia mutations were characterized by gap polymerase chain reaction (gap-PCR), multiplex PCR (m-PCR) and reverse hybridization and sequencing for both α genes. A total of nine α-thal mutations were characterized including four deletional ones: -α(3.7) (rightward), - -(MED-I), -(α)(20.5), -α(4.2) (leftward) and five nondeletional ones: α(polyA1)α, αα(Adana), α(-5 nt)α, α(CS)α and α(polyA2)α. These determinants were arranged in 12 different genotypes, the most frequent of which were: -α(3.7)/αα, - -(MED-I)/αα, -α(3.7)/-α(3.7), α(polyA1)α/αα, αα(Adana)/αα and -(α)(20.5)/αα. This pattern is similar to that reported in Turkey, western (W) Iran, Cyprus and Greece, and to some extent, different from the pattern observed in the Arabian Peninsula.

Strategies for basic laboratory diagnostics of the hemoglobinopathies in multi-ethnic societies: interpretation of results and pitfalls

The consistent multi-ethnic migrations of the last decades have considerably changed the epidemiology of the hemoglobinopathies. Healthy carriers of these conditions are present today in many nonendemic parts of the world, and severely affected children are now born where these diseases were previously rare or unknown. Improving the competence in carrier diagnostics at the laboratory level is one of the first concerns when introducing management and primary prevention of the severe conditions in nonendemic areas. This review describes how and when carriers should be correctly diagnosed and informed. The essential technologies needed for basic carrier diagnostics in different situations are summarized in some detail, and interpretation of the results and a number of related problems are discussed. The role of the hematology laboratory is essential, particularly in nonendemic areas where the first line of health care is often insufficiently aware of hemoglobinopathy management. Carriers living in nonendemic areas can be appropriately diagnosed and informed regarding genetic risk and prevention by well-organized laboratories. Both basic and specialized diagnostics are needed for the correct treatment for the anemic carriers, for primary prevention in couples at risk and for state-of-the art care of severely affected patients.

Study of three families with Hb Agrinio [α29(B10)Leu→Pro, CTG>CCG (α2)] in the Spanish population: three homozygous cases

Most α-thalassemia (α-thal) mechanisms are deletions of one or both α-globin genes and less than 5.0-10.0% are point mutations. Hb Agrinio [α29(B10)Leu→Pro, CTG>CCG (α2)] is a hyperunstable α chain structural variant in which the thalassemic phenotype is determined by a post translational precipitation of the structurally anomalous chain in erythroid precursors. This study involved 14 cases with Hb Agrinio from three families. Selective sequencing of the α2 gene showed a CTG(Leu)>CCG(Pro) mutation at codon 29. The mutation was found in a heterozygous state in 11 cases and in a homozygous state in three cases. These are the first cases with Hb Agrinio described in Spain. In all cases where a leucine is exchanged for a proline, an unstable hemoglobin (Hb) will occur both in the α and the β chain. Some of these are as unstable as Hb Agrinio and their presence is difficult to detect except by DNA sequencing.

Inherited hemoglobin disorders in an Afro-Amazonian community: Saracura

The most common hemoglobinopathies, viz, hemoglobins S and C, and α- and β-thalassemias, were investigated through the molecular screening of 116 subjects from the community of Saracura, comprising fugitive African slaves from farms of the municipality of Santarém, in the west of Pará State, Brazilian Amazon. The observed frequency of the HBB*S gene (0.9%) was significantly lower than that encountered in other Afro-derived communities in the region. Concomitantly, the absence of the HBB*C allele has been reported for most of the Afro-Amazonian communities thus far studied. As remnant populations of quilombos are generally small, the heterogeneous distribution of HBB*S and HBB*C alleles among them is probably due to genetic drift and/or founder effect. The observed frequency of 3.7 kb deletion in Saracura (8.5%) was consistent with the African origin of the population, with a certain degree of local differentiation and admixture with individuals of Caucasian ancestry, placed in evidence by the occurrence of - -(MED) deletion (1.2%), a common mutation in Mediterranean regions. As regards β-thalassemia, among the seven different mutations found in Saracura, three β^o and two β⁺ mutations were of Mediterranean origin, and two β⁺ of African. Thus, only 28% of the local β-thalassemia mutations found in Saracura were of African origin.

Mutation analysis of Netrin 1 and HMX3 genes in patients with superior semicircular canal dehiscence syndrome

CONCLUSION

In spite of its absence in the control population, there is questionable evidence for the alteration c.114C->T in the HMX3 gene being implicated in the development of superior semicircular canal dehiscence (SSCD). However, the concept of a complex disease is valid for SSCD and a possible molecular origin can neither be confirmed nor excluded by the results of this study.

OBJECTIVES

SSCD was first described in 1998 by Minor et al. While the etiology is not clear, findings from both temporal bone CT and histologic studies suggest a congenital or developmental origin. In recent years, a couple of genes regulating inner ear morphogenesis have been described. Specifically, Netrin-1 and HMX3 have been shown to be critically involved in the formation of the SCC. Molecular alterations in these two genes might lead to a disturbed development of this canal and might represent an explanation for SSCD.

METHODS

DNA was extracted from whole blood of 15 patients with SSCD. The coding sequences of Netrin-1 and HMX3 were amplified by PCR and sequenced.

RESULTS

One sequence alteration, heterozygous c.114C->T (conservative change without alteration of amino acid) in exon 1 of HMX3, was detected in 2 of 15 patients but not in 300 control chromosomes. The study was supported in part by the Emilia-Guggenheim-Schnurr-Foundation, Basel, Switzerland.

Recent advances in the molecular understanding of non-transfusion-dependent thalassemia

Thalassemias are a group of inherited autosomal recessive hematologic disorders that occur because of defects in the alpha (α)- and beta (β)-globin genes of adult hemoglobin (Hb). An imbalance in the synthesis of one or more of the globin chains can result in a wide spectrum of phenotypes depending on the type and amount of globin synthesized and additional genetic modifiers. In patients with thalassemia intermedia, a condition known as non-transfusion-dependent thalassemia (NTDT), transfusion requirements are absent or episodic. Non-transfusion-dependent thalassemia includes β-thalassemia intermedia, HbE β-thalassemia, and α-thalassemia intermedia, also known as Hb H disease. This article focuses on the molecular features and genetic mutations specific to NTDT.

Advances in the treatment of alpha-thalassemia

Alpha (α)-thalassemia represents a group of recessively inherited hemoglobin disorders marked by deficient or absent synthesis of 1 to all 4 of the α-globin genes. Inactivation of 3 α-globin genes--either by deletional or nondeletional mutations--results in hemoglobin H (Hb H) disease. Patients with Hb H disease produce hemoglobin composed of all beta chains and have moderate to severe hemolytic anemia, a variable degree of ineffective erythropoiesis, and splenomegaly. Transfusion requirements vary depending on the mutation and clinical severity. Treatment for deletional Hb H disease is primarily preventative and transfusions are uncommon. Patients with nondeletional Hb H disease (e.g., Hb H Constant Spring) typically have more severe anemia, and approximately one-third require regular transfusions. These patients often require comprehensive, multidisciplinary care. This chapter focuses on screening, diagnosis, and treatment approaches for patients with Hb H disease.

Candidate diseases for prenatal gene therapy

Prenatal gene therapy aims to deliver genes to cells and tissues early in prenatal life, allowing correction of a genetic defect, before irreparable tissue damage has occurred. In contrast to postnatal gene therapy, prenatal application may target genes to a large population of stem cells, and the smaller fetal size allows a higher vector to target cell ratio to be achieved. Early gestation delivery may allow the development of immune tolerance to the transgenic protein, which would facilitate postnatal repeat vector administration if needed. Moreover, early delivery would avoid anti-vector immune responses which are often acquired in postnatal life. The NIH Recombinant DNA Advisory Committee considered that a candidate disease for prenatal gene therapy should pose serious morbidity and mortality risks to the fetus or neonate, and not have any effective postnatal treatment. Prenatal gene therapy would therefore be appropriate for life-threatening disorders, in which prenatal gene delivery maintains a clear advantage over cell transplantation or postnatal gene therapy. If deemed safer and more efficacious, prenatal gene therapy may be applicable for nonlethal conditions if adult gene transfer is unlikely to be of benefit. Many candidate diseases will be inherited congenital disorders such as thalassaemia or lysosomal storage disorders. However, obstetric conditions such as fetal growth restriction may also be treated using a targeted gene therapy approach. In each disease, the condition must be diagnosed prenatally, either via antenatal screening and prenatal diagnosis, for example, in the case of hemophilias, or by ultrasound assessment of the fetus, for example, congenital diaphragmatic hernia. In this chapter, we describe some examples of the candidate diseases and discuss how a prenatal gene therapy approach might work.

Prevalence of α-thalassemia 3.7 kb deletion in the adult population of Rio Grande do Norte, Brazil

α-Thalassemia, arising from a defect in α-globin chain synthesis, is often caused by deletions involving one or both of the α-genes on the same allele. With the aim of investigating the prevalence of α-thalassemia 3.7 kb deletion in the adult population of Rio Grande do Norte, 713 unrelated individuals, between 18 and 59 years-of-age, were analyzed. Red blood cell indices were electronically determined, and A₂ and F hemoglobins evaluated by HPLC. PCR was applied to the molecular investigation of α-thalassemia 3.7 kb deletion. Eighty (11.2%) of the 713 individuals investigated presented α-thalassemia, of which 79 (11.1%) were heterozygous (-α^3.7/αα) deletions and 1 (0.1%) homozygous (-α^3.7/-α^3.7). Ethnically, heterozygous deletions were higher (24.8%) in Afro-Brazilians. Comparison of hematological parameters between individuals with normal genotype and those with heterozygous α⁺-thalassemia showed a statistically significant difference in the number of erythrocytes (p < 0.001), MCV (p < 0.001), MCH (p < 0.001) and Hb A₂ (p = 0.007). This study is one of the first dedicated to investigating α-thalassemia 3.7 kb deletion in the population of the State Rio Grande do Norte state. Results obtained demonstrate the importance of investigating this condition in order to elucidate the causes of microcytosis and hypochromia.

Immigration and changes in the epidemiology of hemoglobin disorders in Italy : an emerging public health burden

BACKGROUND

In the last years Italy is confronting with massive migratory movements from developing countries where hemoglobinopathies are widespread. This is causing a large diffusion and a changing spectrum in the epidemiology of hemoglobin disorders in Italy.

METHODS

Investigations recently published in Italy on hemoglobinopathies among immigrants were revised in order to appreciate the impact of immigration from developing countries on epidemiology of these pathologies and to outline adequate guidelines of prevention.

RESULTS

Although in Italy there is a limited number of investigations regarding the relation between immigration and hemoglobin disorders, published data show that in our Nation there is a changing and increasing spectrum of hemoglobinopathies linked to immigration.

CONCLUSIONS

Prospective and retrospective actions of public healthy preventive policy are requested, based upon information (health educational programs for immigrants and caregivers), screenings among immigrants (school screening, pre-marital, preconception and early pregnancy screening, newborn screening), counseling for foreign at-risk couples and healthy carriers.

Zebrafish globin switching occurs in two developmental stages and is controlled by the LCR

Globin gene switching is a complex, highly regulated process allowing expression of distinct globin genes at specific developmental stages. Here, for the first time, we have characterized all of the zebrafish globins based on the completed genomic sequence. Two distinct chromosomal loci, termed major (chromosome 3) and minor (chromosome 12), harbor the globin genes containing α/β pairs in a 5'-3' to 3'-5' orientation. Both these loci share synteny with the mammalian α-globin locus. Zebrafish globin expression was assayed during development and demonstrated two globin switches, similar to human development. A conserved regulatory element, the locus control region (LCR), was revealed by analyzing DNase I hypersensitive sites, H3K4 trimethylation marks and GATA1 binding sites. Surprisingly, the position of these sites with relation to the globin genes is evolutionarily conserved, despite a lack of overall sequence conservation. Motifs within the zebrafish LCR include CACCC, GATA, and NFE2 sites, suggesting functional interactions with known transcription factors but not the same LCR architecture. Functional homology to the mammalian α-LCR MCS-R2 region was confirmed by robust and specific reporter expression in erythrocytes of transgenic zebrafish. Our studies provide a comprehensive characterization of the zebrafish globin loci and clarify the regulation of globin switching.

Rapid identification of the copy number of α-globin genes by capillary electrophoresis analysis

OBJECTIVES

The current study aimed at the rapid identification of the copy number of α-globin genes for the diagnosis of α-thalassemia.

DESIGN AND METHODS

To identify the copy number of α-globin genes in α-thalassemia, we developed a novel method using a multiplex polymerase chain reaction (PCR) in combination with the CE analysis.

RESULTS

The proposed method provides a rapid detection of the common α-globin gene deletions. Sixty-six patients with α-thalassemia and 46 normal controls were included in the present study. The obtained results showed good correlation with those obtained by gap PCR. Moreover, a low amount of maternal cell contamination in the fetus specimen for the prenatal diagnosis of hemoglobin Barts hydrops fetalis as well as the rare multiplicated α-globin genes can be identified using this method.

CONCLUSION

This method provides a convenient and efficient tool for the rapid identification of the copy number of α-globin genes in α-thalassemia and the individuals with α-globin gene multiplication.

Thalassaemia

Thalassaemia is one of the most common genetic diseases worldwide, with at least 60,000 severely affected individuals born every year. Individuals originating from tropical and subtropical regions are most at risk. Disorders of haemoglobin synthesis (thalassaemia) and structure (eg, sickle-cell disease) were among the first molecular diseases to be identified, and have been investigated and characterised in detail over the past 40 years. Nevertheless, treatment of thalassaemia is still largely dependent on supportive care with blood transfusion and iron chelation. Since 1978, scientists and clinicians in this specialty have met regularly in an international effort to improve the management of thalassaemia, with the aim of increasing the expression of unaffected fetal genes to improve the deficiency in adult β-globin synthesis. In this Seminar we discuss important advances in the understanding of the molecular and cellular basis of normal and abnormal expression of globin genes. We will summarise new approaches to the development of tailored pharmacological agents to alter regulation of globin genes, the first trial of gene therapy for thalassaemia, and future prospects of cell therapy.

Hematologic features of alpha thalassemia carriers

Alpha thalassemia (α-thal) is relatively common worldwide. Most carriers are defective in either one or two alpha globin genes out of four functional ones, with deletions being more common than point mutations. The hematologic features are very important for the selection of the appropriate molecular tests while determining the genotype. The aim of this study was to compare hematologic features of patients with various types of α globin mutations. Hematological indices including red blood cells (RBC), hemoglobin concentration (Hb), mean cell volume (MCV), mean cell hemoglobin (MCH), Mean corpuscular hemoglobin concentration (MCHC) and percentage of Hemoglobin (HBA1, HBA2 and HBF) of seven-hundred and twenty two patients presenting ten different α-thal genotypes were considered. All patients showed reduced MCV and/or MCH values.Moreover, MCV and MCH were lower in patients with two functional alpha globin genes in comparison to patients with one mutated alpha globin gene (P value<0.001). In conclusion, MCV and MCH valuescan be helpful for the selection of the appropriate molecular tests to determine the genotype of alphathalassemia carriers.

Advances in hemoglobinopathy detection and identification

Hemoglobin disorders consist of two different groups, the structural hemoglobin variants and the thalassemias. The structural hemoglobin variants typically are based on the point mutations in the alpha- or beta-globin chain that results in a single-amino acid substitution in the corresponding globin chain, whereas thalassemias are caused by quantitative reduction in globin chain synthesis. Various techniques are applied for the laboratory investigation of these diseases, among them mass spectrometry (MS) for the detection and identification of structural hemoglobin variants and array techniques for the thalassemias. In this review, we present in the first part the most important mass spectrometric techniques applied in hemoglobin variant detection and identification and discuss several important aspects of this analysis technique in hematology. In the second part, the DNA analysis techniques used in hemoglobin analysis, such as reverse hybridization or microarray-based comparative genomic hybridization (CGH) techniques, are briefly discussed.