The interaction of alpha thalassaemia with heterozygous beta thalassaemia

Therapeutic Relevance of Inducing Autophagy in β-Thalassemia

The β-thalassemias are inherited genetic disorders affecting the hematopoietic system. In β-thalassemias, more than 350 mutations of the adult β-globin gene cause the low or absent production of adult hemoglobin (HbA). A clinical parameter affecting the physiology of erythroid cells is the excess of free α-globin. Possible experimental strategies for a reduction in excess free α-globin chains in β-thalassemia are CRISPR-Cas9-based genome editing of the β-globin gene, forcing "de novo" HbA production and fetal hemoglobin (HbF) induction. In addition, a reduction in excess free α-globin chains in β-thalassemia can be achieved by induction of the autophagic process. This process is regulated by the Unc-51-like kinase 1 (Ulk1) gene. The interplay with the PI3K/Akt/TOR pathway, with the activity of the α-globin stabilizing protein (AHSP) and the involvement of microRNAs in autophagy and Ulk1 gene expression, is presented and discussed in the context of identifying novel biomarkers and potential therapeutic targets for β-thalassemia.

Impact of α-Globin Gene Expression and α-Globin Modifiers on the Phenotype of β-Thalassemia and Other Hemoglobinopathies: Implications for Patient Management

In this short review, we presented and discussed studies on the expression of globin genes in β-thalassemia, focusing on the impact of α-globin gene expression and α-globin modifiers on the phenotype and clinical severity of β-thalassemia. We first discussed the impact of the excess of free α-globin on the phenotype of β-thalassemia. We then reviewed studies focusing on the expression of α-globin-stabilizing protein (AHSP), as a potential strategy of counteracting the effects of the excess of free α-globin on erythroid cells. Alternative processes controlling α-globin excess were also considered, including the activation of autophagy by β-thalassemia erythroid cells. Altogether, the studies reviewed herein are expected to have a potential impact on the management of patients with β-thalassemia and other hemoglobinopathies for which reduction in α-globin excess is clinically beneficial.

Prevalence of Hemoglobinopathies in Premarital Screening in the Province of Nigde, Turkey

Hemoglobinopathies are one of the most widespread hereditary disorders in Turkey. The present study aimed to determine the prevalence of hemoglobinopathies in the Nigde province of Turkey. This study was conducted with 2013 individuals who applied for the premarital screening, between January 2019 and December 2021. The complete blood count was measured by an automated hematology analyzer. The types of hemoglobin were determined by high-performance liquid chromatography. A total of 2013 individuals including 951 (47.2%) females and 1062 (52.8%) males, were screened within the premarital screening program, and 67 (3.3%) of them were migrants. 53 out of 2013 (2.63%) individuals were identified as β thalassemia carriers, and five of them were migrants including two from Afghanistan, two from Iran, and one from Georgia. HbC was observed in two cases, a couple from Syria (0.1%), HbD in two cases (0.1%), HbE in one case from Thailand (0.05%), HbS-β-thalassemia in one case (0.05%), delta-β thalassemia in one case (0.05%), and unidentified structural variant in one case (0.05%). Moreover, 183 individuals (9.1%) were considered to have iron deficiency, α-thalassemia, or silent β-thalassemia carrier. These results indicate that the province of Nigde is a relatively risky region regarding hemoglobinopathies. Geographic location and immigrant population may have slightly affected the local prevalence of hemoglobinopathies and could be taken into consideration to ensure the effective implementation of the hemoglobinopathy prevention program.

Update in Laboratory Diagnosis of Thalassemia

Alpha- and β-thalassemias and abnormal hemoglobin (Hb) are common in tropical countries. These abnormal globin genes in different combinations lead to many thalassemic diseases including three severe thalassemia diseases, i.e., homozygous β-thalassemia, β-thalassemia/Hb E, and Hb Bart’s hydrops fetalis. Laboratory diagnosis of thalassemia requires a number of tests including red blood cell indices and Hb and DNA analyses. Thalassemic red blood cell analysis with an automated hematology analyzer is a primary screening for thalassemia since microcytosis and decreased Hb content of red blood cells are hallmarks of all thalassemic red blood cells. However, these two red blood cell indices cannot discriminate between thalassemia trait and iron deficiency or between α- and β-thalassemic conditions. Today, Hb analysis may be carried out by either automatic high-performance liquid chromatography (HPLC) or capillary zone electrophoresis (CE) system. These two systems give both qualitative and quantitative analysis of Hb components and help to do thalassemia prenatal and postnatal diagnoses within a short period. Both systems have a good correlation, but the interpretation under the CE system should be done with caution because Hb A2 is clearly separated from Hb E. In case of α-thalassemia gene interaction, it can affect the amount of Hb A2/E. Thalassemia genotypes can be characterized by the intensities between alpha-/beta-globin chains or alpha-/beta-mRNA ratios. However, those are presumptive diagnoses. Only DNA analysis can be made for specific thalassemia mutation diagnosis. Various molecular techniques have been used for point mutation detection in β-thalassemia and large-deletion detection in α-thalassemia. All of these techniques have some advantages and disadvantages. Recently, screening for both α- and β-thalassemia genes by next-generation sequencing (NGS) has been introduced. This technique gives an accurate diagnosis of thalassemia that may be misdiagnosed by other conventional techniques. The major limitation for using NGS in the screening of thalassemia is its cost which is still expensive. All service labs highly recommend to select the technique(s) they are most familiar and most economic one for their routine use.

Microcytic anemia in children: parallel screening for iron deficiency and thalassemia provides a useful opportunity for thalassemia prevention in low- and middle-income countries

Microcytic anemia in children is commonly attributed to iron deficiency without attempting to find the cause. Inadequate investigations to exclude hemoglobinopathies lead to missed opportunities for identification of thalassemia carriers. Here we aim to describe the relative contribution of iron deficiency and thalassemia to microcytic anemia in children. This hospital-based prospective study was conducted at the Colombo North Teaching Hospital, Ragama, Sri Lanka. All newly diagnosed patients with microcytic anemia were recruited and data were collected using an interviewer-administered questionnaire. Full blood count, blood film, serum ferritin, c-reactive protein, quantification of hemoglobin sub-types and α-globin genotype were performed using 4 ml of venous blood. A total of 104 children (Male- 60.5%) were recruited. Iron deficiency was the cause for anemia in 49% whilst 16% and 10% had α- and β-thalassemia trait respectively. Seven (6.7%) children had co-existing iron deficiency and thalassemia trait while two coinherited α- and β-thalassemia trait. Children with β-thalassemia trait had significantly higher red cell count and lower mean corpuscular volume compared to children with iron deficiency. However, none of the red cell parameters were significantly different between children with α-thalassemia trait and iron deficiency. Iron deficiency contributes only to half of children with microcytic anemia; one-fourth had thalassemia trait. Co-existence of iron deficiency and thalassemia trait or co-inheritance of α- and β-thalassemia trait were found in 9%. Parallel investigation of children with microcytic anemia to diagnose iron deficiency and thalassemia provides an opportunity to identify thalassemia carriers which is beneficial for thalassemia prevention.

Anaemia among females in child-bearing age: Relative contributions, effects and interactions of α- and β-thalassaemia

Introduction

Anaemia in women during pregnancy and child bearing age is one of the most common global health problems. Reasons are numerous, but in many cases only minimal attempts are made to elucidate the underlying causes. In this study we aim to identify aetiology of anaemia in women of child bearing age and to determine the relative contributions, effects and interactions of α- and β-thalassaemia in a region of the world where thalassaemia is endemic.

Methods

A cross sectional study was conducted at the Colombo North Teaching Hospital of Sri Lanka. The patient database of deliveries between January 2015 and September 2016 at University Obstetrics Unit was screened to identify women with anaemia during pregnancy and 253 anaemic females were randomly re-called for the study. Data were collected using an interviewer-administered questionnaire and haematological investigations were done to identify aetiologies.

Results

Out of the 253 females who were anaemic during pregnancy and were re-called, 8 were excluded due to being currently pregnant. Of the remaining 245 females, 117(47.8%) remained anaemic and another 22(9.0%) had non-anaemic microcytosis. Of anaemic females, 28(24.8%) were iron deficient, 40(35.4%) had low-normal serum ferritin without fulfilling the criteria for iron deficiency,18(15.3%) had β-haemoglobinopathy trait and 20(17.0%) had α-thalassaemia trait. Of females who had non-anaemic microcytosis, 14(66.0%) had α-thalassaemia trait. In 4 females, both α- and β-thalassaemia trait coexist. These females had higher levels of haemoglobin (p = 0.06), MCV (p<0.05) and MCH (p<0.01) compared to individuals with only β-thalassaemia trait. A significantly higher proportion of premature births (p<0.01) and lower mean birth weights (p<0.05) were observed in patients with α-thalassaemia trait.

Conclusions

Nearly one third of anaemic females in child bearing age had thalassaemia trait of which α-thalassemia contributes to a majority. Both α- and β-thalassaemia trait can co-exist and have ameliorating effects on red cell indices in heterozygous states. α-Thalassaemia trait was significantly associated with premature births and low birth weight. It is of paramount importance to investigate the causes of anaemia in women of child bearing age and during pregnancy in addition to providing universal iron supplementation.

Prevalence of α(+)-Thalassemia in the Scheduled Tribe and Scheduled Caste Populations of Damoh District in Madhya Pradesh, Central India

This study was carried out to ascertain the allelic frequency of α(+)-thalassemia (α(+)-thal) in Scheduled caste and scheduled tribe populations of the Damoh district of Madhya Pradesh, India. Random blood samples of Scheduled tribe (267) and Scheduled caste (168), considering the family as a sampling unit, were analyzed for the presence of the -α(3.7) (rightward) (NG_000006.1: g.34164_37967del3804) and -α(4.2) (leftward) (AF221717) deletions. α(+)-Thal was significantly higher in the Scheduled tribals (77.9%) as compared to the scheduled caste population (9.0%). About 58.0% scheduled tribals carried at least one chromosome with the -α(3.7) deletion and 20.0% scheduled tribals carried the -α(4.2) deletion. Frequency for the -α(3.7) allele was 0.487 in the scheduled tribal populations in comparison to 0.021 in scheduled castes. Allelic frequency for -α(4.2) was 0.103 and 0.024, respectively, in the above communities. No Hardy-Weinberg equilibrium for α-thal gene (p < 0.05) was detected in the tribal population, indicating the presence of selection pressures in favor of α-thal mutation and adaptation.

Epistasis and the sensitivity of phenotypic screens for beta thalassaemia

Genetic disorders of haemoglobin, particularly the sickle cell diseases and the alpha and beta thalassaemias, are the commonest inherited disorders worldwide. The majority of affected births occur in low-income and lower-middle income countries. Screening programmes are a vital tool to counter these haemoglobinopathies by: (i) identifying individual carriers and allowing them to make informed reproductive choices, and (ii) generating population level gene-frequency estimates, to help ensure the optimal allocation of public health resources. For both of these functions it is vital that the screen performed is suitably sensitive. One popular first-stage screening option to detect carriers of beta thalassaemia in low-income countries is the One Tube Osmotic Fragility Test (OTOFT). Here we introduce a population genetic framework within which to quantify the likely sensitivity and specificity of the OTOFT in different epidemiological contexts. We demonstrate that interactions between the carrier states for beta thalassaemia and alpha thalassaemia, glucose-6-phosphate dehydrogenase deficiency and Southeast Asian Ovalocytosis have the potential to reduce the sensitivity of OTOFTs for beta thalassaemia heterozygosity to below 70%. Our results therefore caution against the widespread application of OTOFTs in regions where these erythrocyte variants co-occur.

Co-inheritance of α-thalassaemia and β-thalassaemia in a prenatal screening population in mainland China

Objective

To determine the prevalence of α-thalassaemia in β-thalassaemia individuals in a Chinese population.

Methods

The standard diagnostic marker for β-thalassaemia was elevation of the Hb A2 level (>3.5%) with low mean corpuscular volume. The common α-thalassaemia mutations were studied by molecular analysis in all identified β-thalassaemia carriers.

Results

A prevalence rate of 3.3% for β-thalassaemia was found in our population; α- and β-thalassaemia interactions were found to co-exist in 17.8% of the β-thalassaemia carriers. The -SEA deletion was the most common α-thalassaemia mutation co-inherited with β-thalassaemia, followed by the -α3.7 deletion, the -α4.2 deletion, Hb Quong Sze, and Hb Constant Spring.

Conclusion

Our results suggest that it could be valuable to study co-existing α-globin mutations in subjects with β-thalassaemia trait in a prenatal screening programme, especially in populations with a high prevalence of haemoglobinopathies.

Problems in determining thalassemia carrier status in a program for prevention and control of severe thalassemia syndromes: a lesson from Thailand

BACKGROUND

Prevention and control of severe β thalassemia by carrier detection and identification of couples at risk in developed countries is one of the most successful stories in modern medicine. Similar programs in developing countries especially Southeast Asia, are more problematic because both α and β thalassemias are highly prevalent. In Thailand, there are limited data on whether we could determine, based on hematological phenotypes, the mutation severity and/or coinheritance of α thalassemia in β thalassemia traits.

METHODS

Comprehensive molecular, hematology and hemoglobin analyses of the α and β globin genes were performed in 141 healthy individuals identified as β thalassemia carriers.

RESULTS

Seventeen different β globin mutations were successfully identified out of all cases analyzed. Although the majority of the mutations identified were the β⁰ or severe β⁺ thalassemia alleles, a high proportion of mild mutations (25%) was observed. Of these β thalassemia traits, 22.3% were found to co-inherit the α thalassemias. Milder hematological phenotypes were noted in β⁺ compared with β⁰ thalassemia traits when the α globin genes were intact. Although co-inheritance of α⁰ thalassemia might be suspected in cases with skewed profiles, due to the overlapping values, it remains difficult to apply these parameters for reliable carrier determination.

CONCLUSIONS

A combination of hemoglobin analysis and DNA testing seems to be the best way to confirm carrier status in a region with high frequency for both α and β thalassemias. Underdiagnoses of carrier status could hamper the effectiveness of a thalassemia prevention and control program.

Association of Low Serum Iron with Alpha Globin Gene Deletions and High Level of HbF with Xmn-1 Polymorphism in Sickle Cell Traits

Usually sickle cell traits are asymptomatic but co-existence of various factrors may alter the clinical as well as biochemical levels. In India sickle cell traits are neglected condition. Here we are presenting the alpha deletion in association with low serum iron and increased HbF level with Xmn-1 carriers in sickle cell traits. Sickle traits with alpha deletions had significantly low level of serum iron (P-value <0.05) with low level of reticulocytes and red cell indices while Xmn-1 polymorphism associated with increased HbF level. Study concludes low serum iron associated with alpha deletions and high level of HbF associated with Xmn-1 polymorphism in sickle cell traits.

Genotypic influence of α-deletions on the phenotype of Indian sickle cell anemia patients

BACKGROUND

Some reports have shown that co-inheritance of α-thalassemia and sickle cell disease improves hematological parameters and results in a relatively mild clinical picture for patients; however, the exact molecular basis and clinical significance of the interaction between α-thalassemia and sickle cell disease in India has not yet been described. There is little agreement on the clinical effects of α-thalassemia on the phenotype of sickle cell disease.

METHODS

Complete blood count and red cell indices were measured by an automated cell analyzer. Quantitative assessment of hemoglobin variants HbF, HbA, HbA(2), and HbS was performed by high performance liquid chromatography (HPLC). DNA extraction was performed using the phenol-chloroform method, and molecular study for common α-deletions was done by gap-PCR.

RESULTS

Out of 60 sickle cell anemia patients, the α-thalassemia genotype was found in 18 patients. Three patients had the triplicated α-genotype (Anti α-3.7 kb), and the remaining patients did not have α-deletions. This study indicates that patients with co-existing α-thalassemia and sickle cell disease had a mild phenotype, significantly improved hematological parameters, and fewer blood transfusions than the patients with sickle cell anemia without co-existing α-deletions.

CONCLUSION

Co-existence of α-thalassemia and sickle cell anemia has significant effects on the phenotype of Indian sickle cell patients.

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.

Evaluation of the free α-hemoglobin pool in red blood cells: a new test providing a scale of β-thalassemia severity

β-Thalassemias are characterized by an imbalance of globin chains with an excess of α-chains which precipitates in erythroid precursors and red blood cells (RBCs) leading to inefficient erythropoiesis. The severity of the disease correlates with the amount of unpaired α-chains.Our goal was to develop a simple test for evaluation of the free α-hemoglobin pool present in RBC lysates. Alpha-Hemoglobin Stabilizing Protein (AHSP), the chaperone of α-Hb, was used to trap excess a-Hb. A recombinant GST-AHSP fusion protein was bound to an affinity micro-column and then incubated with hemolysates of patients. After washing, the α-Hb was quantified by spectrophotometry in the elution fraction. This assay was applied to 54 patients: 28 without apparent Hb disorder, 20 β-thalassemic and 6 α-thalassemic. The average value of free α-Hb pool was 93 ± 21 ppm (ng of free α-Hb per mg of Hb subunits)in patients without Hb disorder, while it varies from 119 to 1,756 ppm, in β-thalassemic patients and correlated with genotype. In contrast,the value of the free α-Hb pool was decreased in α-thalassemic patients (65 ± 26 ppm). This assay may help to characterize β-thalassemia phenotypes and to follow the evolution of the globin chain imbalance(α/β+γ ratio) in response to treatment.

Molecular characterization of alpha-thalassemia in the Dohuk region of Iraq

The molecular basis of alpha-thalassemia (alpha-thal) has been addressed by several studies from the eastern Mediterranean region, but not from Iraq. To address this issue, we studied 51 individuals with unexplained hypochromia and/or microcytosis, as well as nine patients with documented Hb H disease from the Dohuk region in northern Iraq. We used multiplex gap-polymerase chain reaction (gap-PCR), reverse hybridization, and sequencing for this purpose. It was found that the most common genotypes in those with unexplained hypochromia and/or microcytosis were -alpha(3.7)/alpha alpha, followed by - -(MED-I)/alpha alpha, then -alpha(3.7)/-alpha (3.7), respectively, detected in 84.3% of the above individuals. Other genotypes identified sporadically were -alpha(4.2)/alpha alpha, alpha(poly A1)alpha/alpha alpha (AATAAA>AATAAG), alpha(Adana)alpha/alpha alpha [Hb Adana, codon 59 (Gly-->Asp) or HBA1:c.179G>A], and alpha(Evanston)alpha/alpha alpha [Hb Evanston, codon 14 (Trp-->Arg) or HBA1:c.43 T>C]. Three cases (5.88%) remained uncharacterized even after sequencing. All nine Hb H cases carried the -alpha(3.7)/- -(MED-I) genotype. Such findings are rather different from those in other eastern Mediterranean populations, particularly with relevance to an Hb H molecular basis.

Genetic modifiers of the beta-haemoglobinopathies

Identification of the molecular basis of the beta-thalassaemias and sickle cell disease (SCD) has made it clear that patients with the same beta-globin genotypes can have very variable patterns of clinical expression. Extensive biochemical and pathophysiological studies over the last 50 years have derived two major modifiers--innate ability to produce fetal haemoglobin and co-inheritance of alpha-thalassaemia, subsequently validated by family and population studies. However, these two modifiers do not explain the full clinical spectrum. Genetic studies have been successful in identifying modifiers if the loci have a major clinical effect and if the genetic variants are common. It is possible that additional modifiers could be uncovered using genetic approaches but success will depend on large sample sizes of well-characterised patients with well-defined phenotypes. Since some of the complications, such as overt stroke in SCD, are relatively rare events, intermediate end-points that contribute to the phenotype, such as Transcranial Doppler velocity (a major predictor of stroke in SCD), could be integrated within the genetic analysis. Integrating multiplex genetic testing with clinical and laboratory data to generate predictive models shows potential, but such genetic approaches also require large datasets.

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.

Heterocellular hereditary persistence of fetal haemoglobin affects the haematological parameters of beta-thalassaemia trait

To assess and define the effects of heterocellular hereditary persistence of fetal haemoglobin (HPFH) on the haematological phenotype of heterozygous beta-thalassaemia, we have studied a large kindred that included a total of 204 subjects with 60 beta-thalassaemia carriers, of whom 35 were also heterozygous, and five homozygous, for heterocellular HPFH. The study was possible because of the homogeneity of the beta-thalassaemia mutation and the ability to genotype the heterocellular HPFH allele. Heterocellular HPFH had a significant effect on the mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV) and haemoglobin (Hb) A2 values in the beta-thalassaemia carriers and accounted for 29%, 30% and 24% of their respective variances. beta-thalassaemia subjects with heterocellular HPFH had higher MCV and MCH values, concomitant with lower levels of Hb A2, and a reduced ineffective erythropoiesis. We conclude that co-inheritance of heterocellular HPFH leads to a primary increase in gamma-chain synthesis in beta-thalassaemia trait and can be another confounding factor in the use of red cell indices and Hb A2 levels in population screening for beta-thalassaemia.

Diversity of alpha-globin mutations and clinical presentation of alpha-thalassemia in Israel

Alpha-thalassemia is among the world's most common single gene disorders, caused primarily by gene deletions. In Israel, where alpha(o)-trait thalassemia is uncommon, it is of particular importance because of its phenotypic interactions with beta-thalassemia in hetero- and homozygotes. In a study of 232 individuals referred for molecular evaluation of anemia, 303 chromosomes carried alpha-globin gene abnormalities; 6 gene rearrangements and 11 point mutations were identified. This unexpected heterogeneity is in part due to the many ethnic subgroups represented by these patients. Our findings include nine unique Israeli alleles, 3 of which are described here for the first time. An equal number of point mutations was found in the alpha2-globin gene as compared to alpha1. A threonine deletion in codon 39 of the alpha1-globin gene, found frequently in Arabs, is unique to Israel and probably represents one of several indigenous alleles. Among Arabs, point mutations were more frequent than large deletions. Surprisingly, in Ashkenazi Jews, who resided for many centuries in a nonmalarial environment, a single alpha-globin gene deletion -alpha(3.7) was found in many cases. The clinical presentation of individuals carrying two or more alpha-globin lesions was highly variable. In general, the severity correlated inversely with the number of functional alpha-globin genes. In some cases, impairment of two alpha-globin genes by point mutations led to a thalassemia-intermedia-like picture which could be misdiagnosed as beta-thalassemia. We conclude that alpha-thalassemia is phenotypically and genotypically more heterogeneous than previously recognized. DNA analysis is invaluable as it provides a specific diagnosis and enables reliable genetic counseling.

Erythroid Maturation and Globin Gene Expression in Mice With Combined Deficiency of NF-E2 and Nrf-2

NF-E2 binding sites, located in distant regulatory sequences, may be important for high level α- and β-globin gene expression. Surprisingly, targeted disruption of each subunit of NF-E2 has either little or no effect on erythroid maturation in mice. For p18 NF-E2, this lack of effect is due, at least in part, to the presence of redundant proteins. For p45 NF-E2, one possibility is that NF-E2–related factors, Nrf-1 or Nrf-2, activate globin gene expression in the absence of NF-E2. To test this hypothesis for Nrf-2, we disrupted the Nrf-2 gene by homologous recombination. Nrf-2–deficient mice had no detectable hematopoietic defect. In addition, no evidence was found for reciprocal upregulation of NF-E2 or Nrf-2 protein in fetal liver cells deficient for either factor. Fetal liver cells deficient for both NF-E2 and Nrf-2 expressed normal levels of α- and β-globin. Mature mice with combined deficiency of NF-E2 and Nrf-2 did not exhibit a defect in erythroid maturation beyond that seen with loss of NF-E2 alone. Thus, the presence of a mild erythroid defect in NF-E2–deficient mice is not the result of compensation by Nrf-2.

Erythroid Maturation and Globin Gene Expression in Mice With Combined Deficiency of NF-E2 and Nrf-2

NF-E2 binding sites, located in distant regulatory sequences, may be important for high level α- and β-globin gene expression. Surprisingly, targeted disruption of each subunit of NF-E2 has either little or no effect on erythroid maturation in mice. For p18 NF-E2, this lack of effect is due, at least in part, to the presence of redundant proteins. For p45 NF-E2, one possibility is that NF-E2–related factors, Nrf-1 or Nrf-2, activate globin gene expression in the absence of NF-E2. To test this hypothesis for Nrf-2, we disrupted the Nrf-2 gene by homologous recombination. Nrf-2–deficient mice had no detectable hematopoietic defect. In addition, no evidence was found for reciprocal upregulation of NF-E2 or Nrf-2 protein in fetal liver cells deficient for either factor. Fetal liver cells deficient for both NF-E2 and Nrf-2 expressed normal levels of α- and β-globin. Mature mice with combined deficiency of NF-E2 and Nrf-2 did not exhibit a defect in erythroid maturation beyond that seen with loss of NF-E2 alone. Thus, the presence of a mild erythroid defect in NF-E2–deficient mice is not the result of compensation by Nrf-2.

Relationship between genotype and phenotype in monogenic diseases: relevance to polygenic diseases

Since the early descriptions of sickle cell anemia, it has been clear that genotype at a single locus rarely completely predicts phenotype. This paper reviews explanations for phenotypic variability in some monogenic diseases. In cystic fibrosis, there is strong correlation between genotype and pancreatic phenotype but only weak association with respiratory phenotype, possibly due to differential inheritance of alleles at loci controlling susceptibility to respiratory infection. In addition, disease mutations have been shown to have more or less severe effect, depending on other variation within the cystic fibrosis gene. In phenylketonuria, genotype at the phenylalanine hydroxylase locus appears to explain the biochemical phenotype, but not the intellectual status. There may be genetically determined variation in flux through the minor metabolic pathways for phenylalanine, influencing levels of alternative metabolites involved in mental development. Phenotypic discordance in sickle cell anemia and beta-thalassemia has been associated with the co-inheritance of genes for hereditary persistence of fetal hemoglobin. A mouse locus has been identified that influences tumour number in mice with the multiple intestinal neoplasia gene. Understanding of the genetic interactions that determine phenotype in apparently monogenic diseases should lead to clarification of the role of different genes in polygenic diseases with complex inheritance patterns, as well as enhancing the ability to predict the outcome of a disease mutation.

A 12-year preventive program for beta-thalassemia in Northern Sardinia

From 1980 to 1991, 6.3% of the adult population of the province of Sassari, Northern Sardinia, underwent voluntary beta-thalassemia screening. Of the 28,000 subjects examined, 15.7% proved to be heterozygotes for beta-thalassemia. In addition, the screening of 7500 students in 26 villages in Sassari province fixed the frequency of beta-thalassemia in this part of Sardinia at 10.4%. Of the 539 couples at risk to be expected from this figure, the screening detected 43% (234). The data suggest that inductive screening played a major role in the efficiency of this preventive beta-thalassemia program. Follow up of 221 pregnancies found to be at risk for homozygous beta-thalassemia and referred to the Antenatal Diagnosis Service, Cagliari, Southern Sardinia, showed that antenatal diagnosis was carried out in 80% of them. The overall percentage of couples refusing antenatal diagnosis was 10.8%, but over the years the acceptance rate for the procedure increased from 87% to 96%. Atypical hematological findings in 1.5% of 468 members of the couples at risk required globin chain synthesis and molecular analyses to define the precise beta-thalassemia genotype. Heterogeneous "mild" beta-thalassemia mutations as well as coexisting delta-thalassemia were found in silent type I and type II beta-thalassemia carriers which, without chain synthesis and DNA investigations, would have escaped detection.

Hematologic phenotype of the mutations IVS1-n6 (T-->C), IVS1-n110 (G-->A), and CD39 (C-->T) in carriers of beta-thalassemia in Greece

The hematologic phenotype was characterized in heterozygotes for three of the most common beta-thalassemia mutations in the Greek population. The study included 17 carriers of beta++ IVS1-n6 (T-->C), 21 carriers of beta+ IVS1-n110 (G-->A), and 17 carriers of beta 0 CD39 (C-->T). The 55 beta-thalassemia heterozygotes were selected from among parents of patients on regular transfusion regimens, and the beta-thalassemia mutation was identified by means of the polymerase chain reaction to amplify the appropriate region of the beta-globin gene and then by allele-specific oligonucleotide hybridization. The assessment of hematologic phenotype included complete blood count and quantitation of hemoglobin HbA2 and HbF and of the globin chain biosynthesis ratio. Comparison and statistical analysis of the hematologic parameters for the three mutations demonstrated no consistent correlation among the three mutations relative to Hb levels, hematocrit, and red cell indices, although heterozygotes for the IVS1-n6 mutation produce red blood cells with slightly higher mean corpuscular volume; significantly lower values of HbA2 (mean, 3.81% +/- 0.62% with four values less than 3.60%) in IVS1-n6 heterozygotes compared with IVS1-n110 heterozygotes (mean, 4.69% +/- 0.48%) and CD39 heterozygotes (mean, 4.75% +/- 0.50%, P < 0.001); and significantly higher HbF levels in CD39 heterozygotes (mean, 2.31% +/- 1.52%) compared with IVS1-n6 heterozygotes (mean, 0.79% +/- 0.45%, P < 0.01) and IVS1-n110 heterozygotes (mean, 1.17% +/- 0.75%, P < 0.01). With respect to the HbA2 levels, the findings are in agreement with previous studies in Mediterranean populations; the slightly higher levels of HbF in CD39 heterozygotes appear to be reported for the first time.

Normal individuals with high Hb A2 levels

Increased haemoglobin (Hb) A2 levels associated with reduced mean corpuscular volume (MCV) and Hb content per cell (MCH) are the most typical features of heterozygous beta thalassaemia. However, double heterozygotes for alpha and beta thalassaemia may have normal MCV and MCH but Hb A2 always in the carrier range. In this report we describe two Sardinian families who have increased Hb A2 levels, normal red blood cell indices and normal globin chain synthesis and in whom DNA sequence analysis of beta and delta globin genes did not reveal any abnormality. Our findings demonstrate the existence of a genetic trait not resulting from a defect of the beta globin gene cluster, transmitted in a dominant manner and manifested as isolated increase of Hb A2.

Screening and prenatal diagnosis of the haemoglobinopathies

In this paper we have reviewed the social and technical aspects of carrier screening and prenatal diagnosis of the inherited haemoglobinopathies. The characteristics of programmes based on carrier screening and prenatal diagnosis ongoing in a number of at-risk Mediterranean populations have been described. The most relevant and common aspects of these programmes are the continuous educational campaign directed to the population at large, the voluntary basis and non-directive counselling. The target population has been most commonly couples before or after marriage. The vast majority of couples counselled accepted prenatal diagnosis. All programmes have encountered a high degree of success as indicated by the marked reduction in the birth rate of infants with thalassaemia major. No significant adverse effects have been reported. A programme with similar characteristics and for which the preliminary results are encouraging, is operating for sickle cell anaemia in the Cuban population. In a population with high frequency of hydrops fetalis, screening for deletion alpha-thalassaemia is recommended to prevent the negative effects on a pregnant woman of the presence of an hydropic fetus. Thalassaemia carrier screening is now carried out by automatic red cell indices and HbA2 determination. Definition of atypical cases may require iron studies, globin chain synthesis determination and/or alpha, beta- and delta-globin gene analysis. Identification of the carrier state is followed by definition of the mutation on enzymatically amplified DNA. Known mutations may be detected by restriction endonuclease analysis, non-denaturing polyacrylamide gel electrophoresis, allele-specific primers or allele-specific probes. The most promising procedures, which are also amenable to complete automation are reverse oligonucleotide hybridization and primer-specific amplification. Unknown mutations are defined by denaturing gradient gel electrophoresis, single-strand conformation polymorphism analysis, and chemical mismatch cleavage analysis followed by direct sequencing. The same methods on enzymatically amplified chorionic villus DNA are used for prenatal diagnosis. The potential pitfall resulting from maternal contamination can be avoided by careful dissection of the maternal decidua from the chorion and by the simultaneous amplification of a suitable polymorphism.

Beta thalassaemia in the indigenous British population

We have analysed the molecular basis of beta-thalassaemia in 22 Anglo-Saxon individuals, all of whom were heterozygous for beta-thalassaemia except for one, who was a compound heterozygote. Using a combination of allele-specific priming of the polymerase chain reaction (PCR) and direct sequencing of genomic DNA amplified by the PCR, 20/23 beta-thalassaemic genes were characterized. Nine different mutations were identified; four are commonly found in the Mediterranean, one in Asia, one has been described previously in both Europe and Asia, and three are rare mutations associated with a dominant beta-thalassaemia phenotype. In three individuals the mutation remains uncharacterized despite sequence analysis of the beta-globin gene and its immediate flanking regions. We report our findings and discuss the diversity of these mutations.

Heterozygous beta-thalassemia: relationship between the hematological phenotype and the type of beta-thalassemia mutation

In this study we have correlated the severity of the hematological features to the type of the beta-thalassemia mutation [codon 39 (C----T), IVS-I nt 110 (G----A), IVS-I nt 1 (G----A), IVS-I nt 6 (T----C), IVS-II nt 745 (C----G), -87 (C----G) and beta 6 (-1 bp)], in a group of beta-thalassemia heterozygotes of Italian descent in whom we excluded the presence of iron deficiency or deletion alpha-thalassemia. The beta-thalassemia mutation was defined by dot blot analysis on amplified DNA with allelic specific oligonucleotide probes. We found that a) heterozygotes for beta+ IVS-I nt 6 and beta+ -87 mutations produce larger and better hemoglobinized red blood cells, and b) heterozygotes for beta+ IVS-I nt 6 and beta+ IVS-I nt 110 mutations have a less marked increase of Hb A2 levels as compared to heterozygotes for the other mutations investigated. These findings indicate that milder beta-thalassemia mutations such as the beta+ IVS-I nt 6 and beta+ -87, express also in the heterozygous state a milder phenotype as compared to beta o-thalassemia or severe beta+ thalassemia (beta+ IVS-I, nt 110). The Hb A2 levels, on the other hand, were not related to the severity of the mutation because of less marked increase was found in a mild (beta+ IVS-I nt 6) as well in a severe (beta+ IVS-I nt 110) mutation. From the practical point of view these findings should be adequately considered in carrier screening and genetic counselling.

Thalassemia: genotypes and phenotypes

The large degree of phenotypic heterogeneity of thalassemia can now be related to the underlying genomic defects. This information has accumulated rapidly over the last years through the recent advances in molecular technology. The list of main types of thalassemia (alpha or beta) that can be differentiated includes several gene deletions (complete or partial) and point mutations (or very short deletions). These occur within the genes or across the flanking DNA sequences and apparently interfere with the expression of these genes. From a quantitative point of view, the severity of the condition is directly related to the amount of functional globin chain mRNA which is made available to the ribosomes; this may vary from zero (gene deletions, frameshift, non-sense mutations or mutations at the splice-junction nucleotides) to very little (mostly hnRNA processing mutants) or to slightly subnormal (transcriptional mutants, mutations resulting in cryptic site activation or in defective cleavage of the poly-A tail). A few hyper-unstable globin chains also produce a thalassemic phenotype. This pattern is straightforward in the alpha-thalassemias. In the beta-thalassemias, the decreased beta-chain synthesis reflects the available mRNA, but the phenotypic expression depends also on the ability of the patient to reactivate gamma-chain synthesis and complement the red cell content with hemoglobin F.

Prenatal diagnosis of thalassemia and hemoglobinopathies in Switzerland

During a 10-month period, 10 couples originating from Africa (3), the tropics (1) and the thalassemia-belt region (6), living in Switzerland, requested prenatal diagnosis of hemoglobinopathies. Hb SS (twice), Hb Bart's (Hydrops fetalis) and beta-thalassemia major were diagnosed either by gene mapping or by direct detection of the mutations in DNA amplified by the PCR procedure. Whenever it was possible to obtain fetal blood or tissue, diagnosis was confirmed. In one Vietnamese man, concomitant existence of alpha-thal 1 with beta-thalassemia resulted in an unusually high Hb level because of balanced alpha and beta globin synthesis. The 10 couples examined originated from 7 different countries and presented at least 7 different Hb pathologies. This variety of pathologies represents the main difficulty for prenatal diagnosis of hemoglobinopathies in a non-endemic country. A diagnostic approach to overcome this problem is developed.

Identification of deletion and triple alpha-globin gene haplotypes in the Montreal beta-thalassemia screening program: implications for genetic medicine

We obtained blood samples in a screening program designed to detect beta-thalassemia heterozygotes in Montreal; additional samples were obtained from referred persons. We analyzed DNA for variant numbers of alpha-globin genes, notably the alpha-thalassemia2 (-alpha/), alpha-thalassemia1, (- -/), and triplicated alpha-globin gene (alpha alpha alpha/) haplotypes using restriction enzymes and probes for alpha-globin and zeta-globin gene sequences. We estimated the numbers of Montreal residents of Italian and Greek ethnic origin with -alpha/alpha alpha genotype. Thus, 4.3% of Italians and 1.5% of Greeks, or about 7,500 persons, are estimated to be alpha-thalassemia2, trait (silent carriers), largely (80%) in the -alpha 3.7/type I form. The triplicated alpha-globin gene haplotype was also found. The risk of a severe (alpha-thalassemia1) phenotype associated with inheritance of - -/alpha alpha or -alpha/-alpha genotypes was low and was found predominantly in this study, in persons of Asian ethnic origin. The sample of Asians was too small to estimate carrier frequencies; however, based on results from the beta-thalassemia screening program, we estimated that about 4% of Asians (about 1,300 persons) in Montreal are alpha-thalassemia carriers. We identified persons heterozygous for both beta-thalassemia and alpha-thalassemia mutations. In these double heterozygotes, the effect of the triplicated alpha-globin gene was to make the erythrocyte parameters used for screening (MCV and %HbA2) more deviant from normal whereas deletion of 2 alpha-globin genes tended to normalize the erythrocyte values. These findings have implications for the screening program and reproductive counseling.

The salience of Garrod's 'molecular groupings' and 'Inborn Factors in Disease'

Garrod's important second book, Inborn Factors in Disease (1931), was about inherited predisposition to disease. Chemical and metabolic individuality, which are the modalities of predisposition, originated in 'molecular groupings' (proteins) in Garrod's view of life. Such 'groupings' as interlocus molecular hybrids, allelic complementation and expressions of modifier genes, can assume variant expression in heterozygotes. Here, it is shown that genetic variation in such 'molecular groupings' has clinical relevance, for example (1) in reproductive counselling for thalassaemia; (2) in heterozygosity where the affected enzymes are normally homopolymeric; (3) in clinical severity of 'monogenic' disease (e.g. familial hypercholesterolaemia and muscular dystrophy) when variation is not explained by allelic heterogeneity. The associated chemical individuality in each case can be used to identify risk and thus as a mode of predictive medicine.

The interaction of alpha thalassaemia and sickle cell-beta zero thalassaemia

The effects of alpha thalassaemia on sickle cell-beta zero thalassaemia have been studied by comparing haematological and clinical features in four subjects homozygous for alpha thalassaemia 2 (2-gene group), 27 heterozygotes (3-gene group), and 55 with a normal alpha globin gene complement (4-gene group). Alpha thalassaemia was associated with significantly higher haemoglobin levels and lower reticulocyte counts independent of the presence of splenomegaly. Contrary to expectation, alpha thalassaemia was associated with small but significant increases in mean cell volume and mean corpuscular haemoglobin concentration. Splenomegaly at age 5 years and episodes of acute splenic sequestration were significantly more frequent in the 4-gene group. There were no significant differences in painful crises, acute chest syndrome, or other clinical features.

The molecular basis of thalassaemia major and thalassaemia intermedia in Asian Indians: application to prenatal diagnosis

A study of the molecular pathology of beta thalassaemia in the Asian Indian immigrant population in the U.K. included 37 patients with thalassaemia major and 14 with thalassaemia intermedia. Using a combination of oligonucleotide probe hybridization and restriction endonuclease analysis the mutations in 100/102 (98%) of the beta thalassaemia genes were characterized. Nine different types were found, of which six are associated with beta zero, one with severe beta+ and two with mild beta+ thalassaemia. Comparison of the beta-globin gene cluster haplotypes, alpha globin genotypes and beta gene mutations of the thalassaemia major group with the thalassaemia intermedia group suggests that the co-inheritance of a high Hb F determinant associated with the - + - + + 5' beta haplotype and the inheritance of a mild beta-thalassaemia mutation are the major ameliorating factors of disease severity in Asian Indians. In comparison with other population groups. beta thalassaemia in Asian Indians is not associated with one or two predominant mutations. Despite this, prenatal diagnosis by direct detection is possible in the majority of families by restriction analysis and a limited number of oligonucleotide probes since the majority of severely affected individuals are homozygous for a single mutation. The characterization of these mutations should be useful for the planning of prenatal diagnosis programmes for beta thalassaemia in other Asian Indian communities.

Interaction of heterozygous beta zero-thalassemia with single functional alpha-globin gene

In this study, we analyzed the phenotypic manifestations resulting from the interaction of heterozygous beta zero-thalassemia(beta zero-39 nonsense mutation) with the functional loss of three alpha-globin structural genes in six subjects, of whom four had the [-alpha/--]alpha-globin genotype and two the [--/alpha Th alpha] alpha-globin genotype. The beta-thalassemia defect was in all cases the nonsense mutation at codon 39. The nondeletion alpha-thalassemia alpha th was the initiation codon mutation (AUG----GUG) of the alpha-2 gene. In all these subjects hypochromia and microcytosis were more marked than in beta zero-thalassemia heterozygotes with a full complement of four alpha-globin genes. All but one had moderate anemia. The alpha:beta globin chain synthesis ratios were consistently decreased. No cases had Hb H on electrophoresis. Subjects with [--/alpha Th alpha] alpha-globin genotype had more severe thalassemia-like manifestations than those with [--/-alpha] alpha-globin genotype.

Pitfalls in genetic counselling for beta-thalassemia: an individual with 4 different thalassemia mutations

This paper describes a complex combination of four thalassemia genes (delta(+), beta(0), nondeletion and deletion alpha-thalassemia) in the spouse of a typical high Hb A2 beta-thalassemia carrier presenting for genetic counselling. This complex gene combination resulted in a hematological phenotype, characterized by thalassemia-like red cell indices, normal Hb A2 and Hb F levels and slightly reduced alpha/beta globin chain synthesis ratio, and therefore not indicative for the presence of beta-thalassemia trait. Family studies in combination with alpha-globin gene mapping, haplotype analysis at the beta-globin gene cluster and definition of the beta-thalassemia mutation by oligonucleotide hybridization led us to identify a beta-thalassemia mutation, to define the molecular basis for this phenotype and give the appropriate genetic counselling.