Suppression of Hb Bart's to improve tissue oxygenation and fetal development in homozygous alpha-thalassemia

Intra-uterine reduction of Hb Bart's only reached with exchange transfusions.

Aberrant glycated haemoglobin (HbA1c) results leading to haemoglobinopathy diagnosis in four Belgian patients

INTRODUCTION

We report four cases in which haemoglobinopathy screening was triggered following aberrant HbA1c analysis. Either the HbA1c assay was unable to produce a quantifiable result or it showed the presence of an extra fraction and/or the result was discordant with the clinical context.

CASE REPORT

In the reported four patients, all from Caucasian, Belgian descent, Hb analysis was performed using cation-exchange high performance liquid chromatography. If necessary, additional Hb electrophoresis was carried out to establish a preliminary (biochemical) diagnosis. Definitive diagnosis was obtained for every sample through DNA-analysis. Three patients were carriers of Hb J-Toronto and one of Hb Stanleyville-II.

DISCUSSION

This report underlines the importance of correct interpretation of HbA1c results to avoid mismanagement of (diabetic) patients. Since neither the RBC indices, the clinical context, nor the ethnicity of these patients was suspicious for an underlying haemoglobinopathy, the aberrant HbA1c result was the only indicator for further investigation. Laboratory personnel and clinicians should be aware of the possibility of uncommon, sometimes clinically unsuspected, Hb variants to cause aberrant HbA1c values, even in populations with low prevalence for haemoglobinopathies. Further analysis should be prompted to obtain definitive diagnosis. Alternative methods for monitoring glycaemic control should be used.

State of the art and new developments in molecular diagnostics for hemoglobinopathies in multiethnic societies

For detecting carriers of thalassemia traits, the basic part of diagnostics consists of measurement of the hematological indices followed by mostly automatic separation and measurement of the Hb fractions, while direct Hb separation either on high pressure liquid chromatography or capillary electrophoresis is sufficient to putatively identify carriers of the common Hb variants like HbS, C, E, D, and O-Arab. A putative positive result is reported together with an advice for parents, partner, or family analysis. For couples, presumed at-risk confirmation at the DNA level is essential. In general, this part of diagnostics is done in specialized centers provided with sufficient experience and the technical tools needed to combine hematological and biochemical interpretation with identification of the mutations at the molecular level. State-of-the-art tools are usually available in centers that also provide prenatal diagnosis and should consist of gap-PCR for the common deletions, direct DNA sequencing for all kind of point-mutations and the capacity to uncover novel or rare mutations or disease mechanisms. New developments are MLPA for large and eventually unknown deletion defects and microarray technology for fine mapping and primer design for breakpoint analysis. Gap-PCR primers designed in the region flanking the deletion breakpoints can subsequently be used to facilitate carrier detection of uncommon deletions in family members or isolated populations in laboratories where no microarray technology or MLPA is available.

Hb Haaglanden: a new nonsickling β7Glu>Val variant. Consequences for basic diagnostics, screening, and risk assessment when dealing with HbS-like variants

INTRODUCTION

To report a new hemoglobin variant undistinguishable from the common HbS on HPLC. To show the efficiency of the simplest confirmation method for HbS and to discuss the implications that may occur if HbS-like variants are wrongly reported as HbS.

METHODS

Basic hematology, separation and measurement of the Hb fractions, 'sickle test,' and molecular analysis.

RESULTS

The abnormal Hb fractions were eluting in the HbS window on HPLC, sickle test was however negative, and DNA sequencing of the beta globin gene revealed an unclassified variant HBBc.23A>T, p.Glu8Val in heterozygous form.

CONCLUSIONS

Although the amino acid substitution of this new variant is identical to that of HbS and shifted of a single amino acid position, no polymerization occurs in vitro. The sickle test is a valid method to confirm or exclude HbS trait in individual cases. Whenever the case is part of a possible couple at risk, then one has to use full DNA analysis in both partners not to miss hidden concomitant defects important for genetic risk predictions.

Relationship between neonatal screening results by HPLC and the number of α-thalassaemia gene mutations; consequences for the cut-off value

Objectives

To evaluate the relationship between FAST peak percentage by adapted Bio-Rad Vnbs analysis using the valley-to-valley integration and genotypes with the aim to improve differentiation between severe α-thalassaemia forms (HbH disease) and the milder disease types.

Method

DNA analysis for α-thalassaemia was performed on 91 dried blood spot samples presenting normal and elevated FAST peak levels, selected during three years of Dutch national newborn screening.

Results

Significant differences were found between samples with and without α-thalassaemia mutations, regardless of the genetic profiles. No significant difference was demonstrated between HPLC in -α/αα and -α/-α, between -α/-α and –/αα and between –/αα and –/-α genotypes.

Conclusion

This study confirms that the percentage HbBart's, as depicted by the FAST peak, is only a relative indication for the number of α genes affected in α-thalassaemia. Based on the data obtained using the modified Bio-Rad Vnbs software, we adopted a cut-off value of 22.5% to discriminate between possible severe α-thalassaemia or HbH disease and other α-thalassaemia phenotypes. Retrospectively, if this cut-off value was utilized during this initial three-year period of neonatal screening, the positive predictive value would have been 0.030 instead of 0.014.

Occurrence of common and rare δ-globin gene defects in two multiethnic populations: thirteen new mutations and the significance of δ-globin gene defects in β-thalassemia diagnostics

INTRODUCTION

The aim of this review is to study the frequency of common and the occurrence of rare and novel mutations of the delta-globin gene and of Hb Lepore defects that might interfere with thalassemia diagnostics and to report the rationale of HbA2 estimation in the presence of delta- or alpha-gene mutations.

METHODS

A total of 135 cases suspected to have a delta-globin gene defect collected in a diagnostic center in the USA and in a reference laboratory in the Netherlands were characterized by molecular analysis.

RESULTS

Hb B2 was found at a frequency of at least 0.5% in the USA and 0.87% in the Netherlands. Known variants such as Hb A2-Babinga, Hb A2-Sphakia, Hb A2-Fitzroy, Hb A2-Flatbush, Hb A2-NYU, Hb A2-Grovetown, HbA2-Yialousa, Hb A2-Indonesia and several delta-thalassemia mutations were found together with 13 new mutations and two new polymorphisms, while Hb Lepores were regularly observed.

CONCLUSION

HbA2 mutations either structurally stable and visible or undetectable because of a thalassemia effect or instability are clinically asymptomatic but may compromise the diagnosis of beta-thalassemia minor. Stable mutations result in two HbA2 fractions of about half of the expected value. Expression defects are undetectable as a protein fraction but reduce the amount of HbA2 by half.

Iron depletion: an ameliorating factor for sickle cell disease?

We report some observations from our laboratory practice that might be important for the treatment of sickle cell disease (SCD). We describe data from two cases indicating that iron depletion might have a beneficial effect diminishing the formation of HbS in favor of HbF, possibly reducing the severity of the disease. We believe that it would be worthwhile to monitor the course of the disease comparing cases with identical genotypes with and without iron depletion, and we advise to consider chelation therapy to reduce iron overload in patients with SCD.

Newborn screening for hemoglobinopathies using capillary electrophoresis technology: Testing the Capillarys Neonat Fast Hb device

OBJECTIVES

To diagnose hemoglobinopathies in newborns by separating and measuring the Hb fractions on high throughput capillary electrophoresis. To test and validate the Capillarys Neonat Fast Hb device (Sebia) on fresh and dry blood samples.

DESIGN AND METHODS

The Hb fractions in 1.600 cord blood samples from the multi ethnic Dutch population were separated and measured. Further, the sensitivity, specificity and reproducibility of the device in detecting abnormalities and measuring the Hb fractions were estimated.

RESULTS

The apparatus separated all significant Hb fractions that should be detected during newborn screening (NBS) with 100% sensitivity. The reproducibility of the migrations guaranteed putative specificity for the few relevant frequent variants observed (HbS, C, and E). The estimation of the HbA and F fractions proved reliable using a well-designed integration mode.

DISCUSSION

Due to the limited number of samples no cases with sickle cell disease or β-thalassemia major were found in this cohort. However, the heterozygous state for the common variants associated with these diseases was clearly recognizable. The measurements were sufficiently precise to recognize sickle cell disease, β-thalassemia major and intermedia and to identify carriers including possible β-thalassemia. Therefore, Capillarys Neonat Fast Hb (Sebia) can be considered as a valid instrument for NBS of the Hemoglobinopathies on fresh and dry blood samples.

Evaluating five dedicated automatic devices for haemoglobinopathy diagnostics in multi-ethnic populations

We have tested five haemoglobin (Hb) separation apparatuses, dedicated to haemoglobinopathy diagnostics. These are the four high performance liquid chromatography devices: VARIANT II, HA 8160, G7, Ultra(2) and the Capillary Electrophoresis apparatus from Sebia. In the first place, we focussed on the capacity of all apparatuses to detect the most common structural variants relevant for public health, these being HbS, HbC, HbE, HbD-Punjab and HbO-Arab. We then compared how the high HbA(2)beta-thalassaemia carriers were identified. All apparatuses were able to identify carriers of these traits with the expected sensitivity and specificity. With the primary goal of a high degree of conformity in basic diagnostics of haemoglobinopathies, we present the interpretation and the significance of the results on all apparatuses, and we comment on the unavoidable problems and solutions.

A new deletion defect leading to ?-thalassaemia in a large Dutch Caucasian family

alpha-thalassaemia is a common inherited haemoglobin disorder that can cause only mild symptoms in carriers and is often either not diagnosed or mistaken for iron deficiency anaemia in the Netherlands. Although considered rare in North-Europeans, we also regularly observe common and rare defects in this population. It is important to be alert for the mild symptoms of these carriers because compound heterozygous and homozygous combinations can result in intermediate, severe or fatal disease in the progeny of healthy carriers. Using a new technical application, a novel alpha degrees -thalassaemia deletion was recently detected in our laboratories in a propositus of a large Dutch Caucasian family. We report the phenotypic and molecular study of this new form of alpha(o)-thalassaemia (called--(OH)alpha-thalassaemia deletion), which was observed in 10 of the 19 individuals studied in the index family. Our results indicate that the frequency of these unsuspected alpha(o)-thalassaemia defects is probably underestimated in the Netherlands.

[Prevention of hereditary haemoglobinopathies in The Netherlands]

Haemoglobinopathies are defects that interfere with the synthesis of haemoglobin. Parents who are both healthy carriers (heterozygotes) may produce severely affected homozygous or compound heterozygous children who can be treated only symptomatically. Offering Dutch couples at risk the possibility of primary prevention is a matter of good healthcare and its organisation deserves priority. The prevention of haemoglobinopathy is based on the provision of information to potential carriers, carrier diagnostics and counselling, services that can in principle be provided by existing public health care institutions. Three moments at which the prevention of recessive diseases can be offered are the phase of preconception, the phase of early pregnancy (prospective primary prevention) and the postnatal phase at the time of a following pregnancy (retrospective primary prevention). By providing basic information and requesting laboratory tests for the diagnosis ofhaemoglobinopathy, the general practitioner plays a crucial role in primary prevention.

Nine unknown rearrangements in 16p13.3 and 11p15.4 causing alpha- and beta-thalassaemia characterised by high resolution multiplex ligation-dependent probe amplification

BACKGROUND

Approximately 80% of the alpha- and 10% of the beta-thalassaemias are caused by genomic deletions involving the alpha- and beta-globin gene clusters on chromosomes 16p13.3 and 11p15.5, respectively. Gap-PCR, Southern blot analysis, and fluorescent in situ hybridisation are commonly used to identify these deletions; however, many deletions go undetected using conventional techniques.

METHODS

Patient samples for which no abnormalities had been found using conventional DNA techniques were analysed by a three colour multiplex ligation-dependent probe amplification assay. Two sets of 35 and 50 probes, covering a region of 700 kb of the alpha- and 500 kb of the beta-globin gene cluster, respectively, were designed to detect rearrangements in the alpha- and beta-globin gene clusters.

RESULTS

In 19 out of 38 patient samples, we found 11 different alpha-thalassaemia deletions, six of which were not previously described. Two novel deletions leaving the alpha-globin gene cluster intact were found to cause a complete downregulation of the downstream alpha-genes. Similarly, 31 out of 51 patient samples were found to carry 10 different deletions involving the beta-globin gene cluster, three of which were not previously described. One involves the deletion of the locus control region leaving the beta-globin gene cluster intact.

CONCLUSIONS

These deletions, which are not easily detected by conventional techniques, may have clinical implications during pregnancy ranging from mild to life threatening microcytic haemolytic anaemia in neonates. The approach as described here is a rapid and sensitive method for high resolution analysis of the globin gene clusters and for any region of the genome.

The molecular spectrum of beta-thalassemia and abnormal hemoglobins in the allochthonous and autochthonous dutch population

The prevalence at birth of hemoglobin defects in the autochthonous North-European population is low. However, the long immigration and colonial history of the Netherlands has resulted in a group of about 1-2 million 'autochthonous' inhabitants, with Asian, South-European or African ancestors, in whom a moderate birth prevalence of globin gene mutations can be expected. Furthermore, at least 10% of the Dutch population consists of recent immigrants from different countries with high birth prevalence of hemoglobinopathies. Because of the endogamous partner choice, which is prevalent in this population, the risk for homozygous progeny remains elevated. At least 100,000 carriers of hemoglobinopathies of recent allochthonous origin are present in the Netherlands, and the number of homozygous children is rising. Prevention by prenatal diagnosis requires a suitable protocol and knowledge about the molecular defects present in the country. Therefore we have analyzed a large number of patients and carriers, both at the hematological and at the DNA level. Our survey revealed 47 different beta-thalassemia determinants, characterized on 223 independent chromosomes from individuals of different ethnic origins. As expected, the most prevalent mutations were largely represented. The cd39 (C-->T) mutation was found in 70% of the immigrants from Morocco, Sardinia and other Central-West-Mediterranean regions while the IVS-I-110 (G-->A) was prevalent in the East-Mediterranean populations. The IVS-I-5 (G-->C) mutation was found in 45% of the patients of Indonesian origin. We also registered 308 independent chromosomes with common structural defects (HbS, HbC, HbE, Hb Lepore, Hb Constant Spring and HbD Punjab) and 33 chromosomes with 19 different, less frequent, rare or very rare mutants. Seven structural mutants were described for the first time and published separately. Furthermore, 139 independent chromosomes with deletional and nondeletional alpha-thalassemia defects were characterized.

Molecular spectrum of alpha-thalassemia in the Iranian population of Hormozgan: three novel point mutation defects

We describe the molecular spectrum of alpha-thalassemia mutations in a population sample of newborns in the South-Iranian province of Hormozgan. Out of 660 randomly collected blood samples 218 (33%) had visibly elevated Hb Bart's. DNA was extracted from 78 samples out of this selection (n=156), of which 114 alleles were found to carry an alpha-thalassemia defect. Besides the common -alpha3.7 (79.1%), -alpha4.2 (1.7%), and alpha-5nt alpha alleles (4.3%), three novel nondeletional alpha-thalassemia mutations were found; the alpha2 cd19 (-G) frameshift mutation (12.2%), the alpha1 IVS1-148(A-->G) (0.9%) affecting the splice acceptor site consensus sequence and the cd14 (TGG-->TAG) (0.9%), which creates a premature stop codon in the first exon of the alpha1-gene. A fourth mutation in the alpha1-gene, the IVS1-38 (C-->T) (0.9%) of undetermined effect, was found in an individual heterozygous for the alpha2 cd19(-G) mutation.

Paediatric allogeneic bone marrow transplantation for homozygous beta-thalassaemia, the Dutch experience

We reviewed the results of the Dutch paediatric bone marrow transplant (BMT) program for children receiving HLA-identical BMT for beta-thalassaemia major over an 18-year period. In all, 19 patients underwent a total of 21 transplants in our treatment centre between July 1984 and February 2002. Eight females (age 0.3-12 years; median 5 years) and 11 males (age 0.8-18 years; median 6 years) were included. Information, prospectively collected, included molecular defects, donor genotype, beta/alpha-globin expression rates, serum ferritin levels, hepato-splenomegaly, chelation history, virology screening, liver pathology together with post-transplant outcome inclusive of leucocyte chimerism. In total, 11 patients received standard busulphan/cyclophosphamide (Bu/Cy) conditioning, with or without ATG. Stable engraftment was seen in 5/11 with late rejection occurring in six patients. Of these, two children underwent a second successful SCT. For this group, overall event-free survival (EFS) and disease-free survival (DFS) were 90 (10/11) and 64% (7/11), respectively. The probability of rejection was 55%. Subsequent addition of melphalan to the conditioning regimen resulted in long-term stable engraftment in all patients with an EFS/DFS for this group of 90% (9/10). Treatment-related mortality, irrespective of conditioning, was low at 5% (1/19 patients). Veno-occlusive disease (VOD) occurred in 19% (4/21 transplants) and acute GvHD in 19% (4/21 transplants). Post-BMT beta/alpha synthetic ratio measurement monitored donor erythroid engraftment and predicted rejection with a return to transfusion dependency. Maintained full donor chimerism is indicative of stable engraftment both for leucocyte and erythroid lineages, whereas mixed donor chimerism is not. Our results emphasise the importance of the conditioning regimen and post-transplant chimerism surveillance predictive of rejection or long-term stable engraftment.

Hemoglobin H disease resulting from the association of the - alpha 3.7 rightward deletion and the (alpha alpha)MM deletion in a Brazilian patient

A patient with Hb H disease resulting from the association of the - alpha 3.7 rightward deletion with the rare (alpha alpha)MM deletion, which removes the entire alpha-major regulatory element (MRE), is reported. This is the first description of an alpha-thalassemic mutation resulting from deletion of the locus-controlling sequences in the South-American population.

Molecular spectrum of beta-thalassemia in the Iranian Province of Hormozgan

Prevention of beta-thalassemia implies knowledge of the molecular spectrum occurring in the population at risk. This knowledge is necessary, especially when a prevention protocol is applied to a multiethnic population. For this purpose, we have recently analyzed a large population of Iranian patients living in the Province of Hormozgan in Iran, and a small group of Iranian patients living in The Netherlands. We have found a different mutation spectrum in both populations as compared to the data obtained by other authors for the Iranian regions of Tehran, Fars, Sistan Balouchestan, Bushehr, and Khouzestan. The IVS-I-5 (G-->C) is the most frequent mutant in the province of Hormozgan (69%), followed by the IVS-II-1 (G-->A) (9.6%), while the IVS-I-1 (G-->A) was the most frequent defect found in the Iranian population sample in The Netherlands. The IVS-II-745 (C-->G) mutation in cis with the 5'UTR (untranslated region) +20 (C-->T) transition was observed in two unrelated, transfusion-dependent homozygotes, living in the Hormozgan Province where, in contrast with populations living in other provinces of Iran, no IVS-I-110 (G-->A) or IVS-I-1 (G-->A) mutations were found. We report the molecular spectra of our population samples and compare them with the mutation spectra observed in the Iranian populations by other authors. We discuss the severe phenotype of the patients homozygous for the IVS-II-745 (C-->G) mutation, linked in cis to the 5'UTR +20 (C-->T) transition. Molecular analysis using commercial kits is briefly compared with denaturing gradient gel electrophoresis, emphasizing the value of a rapid method of detection for molecular defects in areas where many mutations occur.

Different geographic origins of Hb Constant Spring [alpha(2) codon 142 TAA-->CAA]

BACKGROUND AND OBJECTIVES

The occurrence of Hb CS is usually limited to the geographic area which includes Southern China and South East Asia. In 1968 Hb CS was also found to occur in the Mediterranean area where it was originally described as Hb Athens. We investigated the independent origin of these termination codon mutations of the alpha 2-globin gene by determining the alpha-cluster haplotype and comparing the hematologic data from Hb CS-Hb H patients and their family members.

DESIGN AND METHODS

We studied one Hb CS-Hb H patient of Greek origin and a Sicilian family in which one individual was affected by Hb CS-Hb H. The haplotype of the Hb CS allele was determined and compared to the haplotype of an Hb CS-Hb H individual of Chinese origin.

RESULTS

The haplotype found for the Greek and Sicilian Hb CS was the same but differed significantly from the Asiatic Hb CS mutation.

INTERPRETATION AND CONCLUSIONS

The Hb CS mutation found in both Mediterranean patients arose independently in the Mediterranean area. The difference in clinical manifestation of the Hb CS-Hb H disease in both patients is less common but consistent with similar variation in the clinical expression of analogous Hb Icaria-Hb H disease patients.

alpha-thalassaemia as a result of a novel splice donor site mutation of the alpha1-globin gene

We describe the characterization of an alpha+-thalassaemia determinant as a result of a transition of G-->A of the donor splice consensus site sequence of the first intron of the alpha1-globin gene (alpha1IVS I-1). The mutation was found in combination with the South-East Asian alpha0-thalassaemia deletion in an haemoglobin (Hb)H patient and her sister, both of Thai origin. Sequencing of the abnormally spliced mRNA product revealed the presence of a cryptic splice site in exon 1 of the alpha1-globin gene. No normally spliced alpha1mRNA was detected. The abnormally spliced mRNA product from the alpha1-gene carrying the mutation does not lead to functional protein and causes a mild HbH-disease phenotype when in combination with the deletion type alpha0-thalassaemia.

Hb Aghia Sophia [alpha62(E11)Val-->0 (alpha1)], an "in-frame" deletion causing alpha-thalassemia

In this report we describe a case of Hb H disease due to the interaction of the --(MED 1) deletion with a new alpha(+)-thalassemia determinant. The molecular analysis of the proband's genomic DNA was carried out by polymerase chain reaction amplification and sequencing of both alpha genes of the alpha(+)-thalassemia chromosome and revealed a deletion of codon 62 of the alpha1 gene. This DNA triplet codes for a valine residue at the E11 alpha helix, which is located in the interior of the heme pocket. Substitutions of valine E11 with other amino acid residues in the alpha as well as beta polypeptide chains lead, in the heterozygous carrier, either to Hb M disease or to congenital non-spherocytic hemolytic anemia. We assume that the deletion of valine at alpha62(E11) disrupts the conformation of the alpha chain to such an extent that the mutated subunit is rapidly removed by proteolysis. The final result is an alpha-thalassemia phenotype rather than an unstable hemoglobin syndrome. This conclusion is supported by the apparent absence of an abnormal alpha chain in the peripheral blood of the patient.

Haemoglobinopathy analyses in the Netherlands: a report of an in vitro globin chain biosynthesis survey using a rapid, modified method

The paper reports the results obtained from the study of 949 patients examined for a suspected alpha- or beta-thalassaemia using a rapid modified method of in vitro biosynthesis determination. Part of the results have been evaluated in correlation with the different molecular defects, defects combinations and with the presence of abnormal haemoglobins. The validity of the method for diagnosis of thalassaemia and particularly for the analysis of complex defects combinations which may occur in multiethnic populations is illustrated. The technology of the modified method is thoroughly described and the influence of the factors interfering with the reliability of the experiments is discussed.

Hb Nijkerk: a new mutation at codons 138/139 of the beta-globin gene inducing severe hemolytic anemia in a Dutch girl

We describe a new structural mutant of the beta-globin chain in a 17-year-old Dutch Caucasian girl. The mutant is associated with a severe pathology as a consequence of hyper-instability of the hemoglobin tetramer. The proband, whose parents had no history of hemolysis, was admitted to the hospital at 5 months of age with hemolytic anemia and splenomegaly. No indications for autoimmune defects or enzymopathies were found. Repeated hemoglobin electrophoresis on cellulose acetate revealed no abnormalities. At the age of 17 years, a minor abnormal band of less than 1% was detected on starch gel electrophoresis, migrating slightly faster than Hb A2. Sequencing of the beta-globin gene revealed heterozygosity for a 4 bp deletion (GCTA) in combination with a 1 bp insertion (T) at codons 138/139. This event eliminates two amino acids (Ala-Asn) and introduces a new residue (Tyr). We discuss the hematological and the pathophysiological consequences of this mutant, which is fully expressed as a gene product, and apparently assembled into unstable tetramers that precipitate shortly after.

A complex haemoglobinopathy diagnosis in a family with both beta zero- and alpha (zero/+)-thalassaemia homozygosity

The occurrence of point mutation alpha-thalassaemia and of complex combinations of haemoglobin defects is underestimated. Haemoglobinopathies, the most frequent monogenic recessive autosomal disorder in man, occur predominantly in Mediterranean, African and Asiatic populations. However, countries of immigration with a low incidence in the indigenous population, are now confronted with a highly heterogeneous array of imported defects. Furthermore, the occurrence of severe phenotypes is bound to increase in the near future because of the endogamous growth of the ethnical minorities and the lack of prevention. We describe an Afghan family in which both partners of a consanguineous relationship are carriers of a beta- as well as an alpha-thalassaemia determinant. The combination of defects was revealed by the in vitro measurement of the beta/alpha biosynthetic ratio and was characterised at the DNA level. The molecular defects involved are the Cd5(-CT), a Mediterranean beta zero-thalassaemia mutation, and the alpha 2(zero/+)-thalassaemia AATA(-AA) polyadenylation defect. The alpha-thalassemia defect is a rare RNA-processing mutant described only twice before in heterozygous form in Asian-Indian patients. The mutation suppresses the expression of a alpha 2 gene and reduces the expression of the less efficient, 3' located alpha 1 gene as well, inducing a near alpha zero-thalassaemia phenotype. This defect is now described for the first time in the homozygous condition in one of the children who, in addition to being homozygous for the alpha-thalassaemia point mutation, is also a carrier of the beta zero-thalassaemia defect. A previously described homozygous case of the alpha (zero/+)-thalassaemia condition, caused by a similar polyadenylation defect, was characterised by a severe HbH disease. However, the patient described here present at 7 years of age with severe caries, like his beta-thalassaemia homozygous brother but without hepatosplenomegaly, haemolysis or severe anaemia. The haematological analysis revealed 9.5 g/dl Hb; 5.4 x 10(12)/I RBC; 0.33 I/I PCV; 61 fl MCV; 17.6 pg MCH and 6.2% of HbA2. The biosynthetic ratio beta:alpha was 1.6 and no HbH fraction was detectable either on electrophoresis or as inclusion bodies. The parents reported no complications during pregnancy, at birth, or in the neonatal period in rural Afghanistan. We presume therefore that the counterbalancing effect induced by the co-existing beta-thalassaemia defect could have modified a potentially severe perinatal HbH disease into a strongly hypochromic but well compensated 'alpha zero-like heterozygous' thalassaemia phenotype. The risk of a severe HbH disease, could have been easily missed in this family which was referred because of a child affected with beta-thalassaemia major.

Phenotype variability of the dominant beta-thalassemia induced in four Dutch families by the rare cd121 (G-->T) mutation

Eight patients who were carriers of beta-thalassemia induced by the cd121 (G-->T) mutation are described in four nonrelated Dutch families. This mutant, which is considered rare and inherited in a dominant manner, is expressed in a different way among each of the four families and even among carriers of the same family. The symptoms vary from an hemolytic anemia of intermediate gravity with hepatosplenomegaly, inclusion bodies and erythroblastosis, to a mild anemia with minor hematological abnormalities. We report the analytical procedures used for the detection of the mutant, the hematological and clinical data of the four families and discuss the variable physiopathology of this molecular defect. We also compare the variation in fetal hemoglobin expression in relation to the haplotypes of the beta-gene cluster and to the different hematological conditions. The presence of this rare mutant in four nonrelated Dutch families could derive from a single mutation or from multiple events. The existence of the four mutations in three different haplotypes suggests the occurrence of at least two independent events. The presence of five abnormal hemoglobins and the beta-thalassemia defect on different haplotypes at cd121 also suggests a relatively increased rate of mutations at this particular site.

A case of non-beta-globin gene linked beta thalassaemia in a Dutch family with two additional alpha-gene defects: the common -alpha3.7 deletion and the rare IVS1-116 (A-->G) acceptor splice site mutation

We describe a family with beta thalassaemia, apparently not linked to the beta-globin gene cluster, in combination with alpha thalassaemia. The propositus, an adult Dutch Caucasian male, and his son presented with microcytic hypochromic parameters. Their lysates displayed the normal adult pattern on electrophoresis. The HbA2 concentration, which is usually increased in beta thalassaemia, was normal. The in vitro biosynthetic rate of the globin chains was strongly unbalanced even in the presence of a coexisting alpha-thalassaemia defect. Routine analysis of the beta genes, including the promoter region, was performed repeatedly by polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGCE) and direct sequencing. No molecular abnormalities were detected. Large beta deletions were excluded by haplotype determination, using seven polymorphic markers distributed over an area of 50 kb, from 1 kb 5' of the epsilon gene to 4 kb 3' of the beta gene. The haplotype analysis of the beta-gene cluster revealed that the unaffected daughter had received the same beta haplotype as her beta-thalassaemic brother from their beta-thalassaemic father. These data suggest that the beta-gene cluster shared by father and son was not directly associated with a reduced beta-globin chain expression. In order to exclude the remote possibility of a beta-locus-control region (LCR) rearrangement in the paternal haplotype of the daughter, the sequence of the HS2 element was examined in the nuclear family. We compared the haematological and clinical data of this family with the data reported in the limited number of similar cases. We discuss the possibility that the mutation of a trans-acting erythroid factor(s), not linked to the beta-genes cluster, may impair the beta-gene expression of both alleles.

Alpha-thalassaemia

alpha-Thalassaemias are genetic defects extremely frequent in some populations and are characterized by the decrease or complete suppression of alpha-globin polypeptide chains. The gene cluster, which codes for and controls the production of these polypeptides, maps near the telomere of the short arm of chromosome 16, within a G + C rich and early-replicating DNA region. The genes expressed during the embryonic (zeta) or fetal and adult stage (alpha 2 and alpha 1) can be modified by point mutations which affect either the processing-translation of mRNA or make the polypeptide chains extremely unstable. Much more frequent are the deletions of variable size (from approximately 3 to more than 100 kb) which remove one or both alpha genes in cis or even the whole gene cluster. Deletions of a single gene are the result of unequal pairing during meiosis, followed by reciprocal recombination. These unequal cross-overs, which produce also alpha gene triplications and quadruplications, are made possible by the high degree of homology of the two alpha genes and of their flanking sequences. Other deletions involving one or more genes are due to recombinations which have taken place within non-homologous regions (illegitimate recombinations) or in DNA segments whose homology is limited to very short sequences. Particularly interesting are the deletions which eliminate large DNA areas 5' of zeta or of both alpha genes. These deletions do not include the structural genes but, nevertheless, suppress completely their expression. Larger deletions involving the tip of the short arm of chromosome 16 by truncation, interstitial deletions or translocations result in the contiguous gene syndrome ATR-16. In this complex syndrome alpha-thalassaemia is accompanied by mental retardation and variable dismorphic features. The study of mutations of the 5' upstream flanking region has led to the discovery of a DNA sequence, localized 40 kb upstream of the zeta-globin gene, which controls the expression of the alpha genes (alpha major regulatory element or HS-40). In the acquired variant of haemoglobin H (HbH) disease found in rare individuals with myelodysplastic disorders and in the X-linked mental retardation associated with alpha-thalassaemia, a profound reduction or absence of alpha gene expression has been observed, which is not accompanied by structural alterations of the coding or controlling regions of the alpha gene complex. Most probably the acquired alpha-thalassaemia is due to the lack of soluble activators (or presence of repressors) which act in trans and affect the expression of the homologous clusters and are coded by genes not (closely) linked to the alpha genes. The ATR-X syndrome results from mutations of the XH2 gene, located on the X chromosome (Xq13.3) and coding for a transacting factor which regulates gene expression. The interaction of the different alpha-thalassaemia determinants results in three phenotypes: the alpha-thalassaemic trait, clinically silent and presenting only limited alterations of haematological parameters, HbH disease, characterized by the development of a haemolytic anaemia of variable degree, and the (lethal) Hb Bart's hydrops fetalis syndrome. The diagnosis of alpha-thalassaemia due to deletions is implemented by the electrophoretic analysis of genomic DNA digested with restriction enzymes and hybridized with specific molecular probes. Recently polymerase chain reaction (PCR) based strategies have replaced the Southern blotting methodology. The straightforward identification of point mutations is carried out by the specific amplification of the alpha 2 or alpha 1 gene by PCR followed by the localization and identification of the mutation with a variety of screening systems (denaturing gradient gel electrophoresis (DGGE), single strand conformation polymorphisms (SSCP)) and direct sequencing.

Atypical HbH disease in a Surinamese patient resulting from a combination of the -SEA and -alpha 3.7 deletions with HbC heterozygosity

The first case of haemoglobin H (HbH) disease in combination with haemoglobin C (HbC) is reported in a man of Surinamese origin. Only haemoglobin A (HbA) and HbC were detected by electrophoresis. The amount of HbC was much less than expected in HbC heterozygotes. The synthesis ratio (beta A+ beta C/alpha) indicated an alpha-thalassaemia defect with two non-functional alpha genes, which did not correlate with the degree of haemolysis and anaemia displayed by the patient. The DNA analysis of the alpha-genes clusters revealed a defect combination -SEA/-alpha 3.7. The haematological data and the physiopathology of this atypical case are compared with the typical HbH disease found in a first cousin of the propositus. Data on the globin chains expression and on the formation of beta A and beta C homotetramers in HbH/HbC disease are presented.

Characterization and localization of the mProx1 gene directly upstream of the mouse alpha-globin gene cluster: identification of a polymorphic direct repeat in the 5'UTR

The alpha-globin major regulatory element (alpha MRE) positioned far upstream of the gene cluster is essential for the proper expression of the alpha-globin genes. Analysis of the human and mouse alpha-globin Upstream Flanking Regions (alpha UFR) has identified three nonglobin genes in the order Dist1-MPG-Prox1-alpha-globin. Further characterization of the whole region indicates that the alpha MRE and several other erythroid DNase HSSs are associated with the transcription unit of the Prox1 gene. In this paper we describe the characterization and localization of the mouse Prox1 cDNA and compare it with its human homolog, the -14 gene, and another human cDNA sequence named hProx1. Our results show a strong conservation between the -14 gene and the mouse Prox1 gene with the exception of the first exon of the mProx1 gene. This exon is absent in the -14 cDNA but is present and conserved in the human Prox1 cDNA, indicating that the human -14/hProx1 gene is alternatively spliced or transcribed. The mProx1 gene encodes a predicted protein of 491 amino acids (aa) whose function is not known. In the 5'UTR of this gene, a 35-bp repeat (VNTR) is positioned, which is highly polymorphic among laboratory inbred mice (Mus domesticus). Our results strongly suggest that the mProx1 VNTR arose during the divergence of M. spretus and M. domesticus. Besides its use in evolutionary studies and positional cloning, the mProx1 VNTR might be invaluable for monitoring the expression of a transgenic mProx1 gene. The cloning of the mProx1 gene will be helpful to analyze its possible role on alpha-globin as well on MPG expression in the mouse.

An IVS1-116 (A-->G) acceptor splice site mutation in the alpha 2 globin gene causing alpha + thalassaemia in two Dutch families

We report the characterization of an alpha +(-)thalassaemia determinant due to a transition A-->G of the acceptor splice consensus site sequence (IVS1-116) of the first intron of the alpha 2-globin gene. The mutation, found in two apparently unrelated Dutch Caucasian families, was detected by DGGE analysis followed by direct sequencing. Haplotype analysis suggests a common origin of the mutation in both families. The disruption of the acceptor splice site consensus sequence interferes with the correct splicing and leads to the retention of the first intron in the abnormally spliced mRNA. The alpha +(-)thalassaemia phenotype observed in the carriers is caused by the absence of functional mRNA which cannot be replaced by the abnormally spliced mRNA. The low amounts of abnormal mRNA found in reticulocytes is, most probably, due to the post-transcriptional instability which follows the presence of a termination codon in the retained intronic sequence. This situation is often associated with a decreased mRNA stability as observed for several nonsense mutations of the beta-globin gene.

A Dutch family with Hb Atlanta [beta 75(E19)Leu-->Pro]

We have investigated four members of a three-generation Dutch family for a suspected hemoglobinopathy. Chronic hemolysis and a moderate macrocytic normochromic anemia with slight morphological abnormalities of the red cells was observed in all four. Hemoglobin chain synthesis in vitro and separation of the globin chains by reversed phase high performance liquid chromatography revealed an abnormal beta-globin species in addition to the normal alpha and beta chains. The decreased amount of normal beta-globin and the low amount of unidentified protein suggested an unstable beta-globin variant. An abnormal band was detected by isoelectrofocusing. In one family member tested, the hemoglobin in an erythrocyte lysate had decreased heat stability. All carriers were positive in the isopropanol hemoglobin instability test. Treatment of erythrocytes with methylviolet gave rise to microgranular inclusions. Nucleotide sequencing of the polymerase chain reaction-amplified beta-globin gene revealed a heterozygous single base pair T-->C mutation at codon 75, which changes the normal CTG codon for leucine to a CCG codon for proline. This variant has previously been identified as Hb Atlanta or beta 75(E19)Leu-->Pro. The mutation creates a new Msp I restriction site, which was used to confirm the diagnosis in all four family members. A quantitative reverse transcriptase polymerase chain reaction procedure for determining the relative amounts of mRNA transcripts for the normal and abnormal globin chain showed a comparable stability for both transcripts.

Hb Malmö [beta-97(FG-4)His-->Gln] leading to polycythemia in a Dutch family

We have examined six individuals from a two-generation Dutch family for a suspected hemoglobin (Hb) abnormality. The propositus presented with polycythemia and complained of persistent weakness, headache, and epistaxis. All family members initially showed a normal Hb-electrophoretic pattern, but on isoelectric focusing, three of them displayed a fast-moving band associated with high packed red cell volumes (PCV) and increased red blood cell count. The Hb mutant was analyzed at the DNA level by specific gene fragment amplification (PCR), followed by direct DNA sequencing, and the mutation was confirmed by restriction enzyme analysis. We found a C-->G transversion (CAC-->CAG) at codon 97 of the beta-chain, which corresponded to the His-->Gln amino acid substitution previously described as Hb Malmö. We report here the clinical history of the patient, the effects of phlebotomy treatment, and the effect of subnormal iron conditions on the erythropoietic recovery after phlebotomy. The mechanism responsible for the induction of the higher oxygen affinity is discussed, as are some aspects concerning the occurrence, pathology treatment, and the genetic risk of Hb variants with high O2 affinity.

Hb Utrecht [alpha 2 129(H12)Leu-->Pro], a new unstable alpha 2-chain variant associated with a mild alpha-thalassaemic phenotype

We describe a new alpha 2-globin gene point mutation found in six individuals of a three-generation Dutch family. The mutant, which is associated with a mild alpha-thalassaemic phenotype, is not detectable at the protein level. The alpha 2 cd129 (CTG-->CCG) transition was found by molecular analysis using denaturing gradient gel electrophoresis (DGGE) and single-strand conformation analysis (SSCA) followed by direct sequencing of the alpha 2-globin gene. Southern analysis revealed a triplication of the zeta-gene in cis with the mutant alpha-globin gene.

HB Gouda [alpha 72(EF1)His-->Gln], a new silent alpha chain variant

We describe a new alpha chain mutant accidentally found in a diabetic patient. The propositus is being treated for diabetes mellitus II with 4% glycated hemoglobin (Hb A1C). The variant, named Hb Gouda, is not detectable by starch gel electrophoresis but appears as a shoulder before the Hb A fraction during the chromatographic separation of Hb A1C. The hematological analysis revealed normal parameters with a normal serum iron value. No anomalies were reported in connection with Hb Gouda. The tryptic peptide map and sequencing of the alpha T-9 peptide revealed the substitution of a histidine by a glutamine at position 72. By selective amplification and sequencing of both the alpha genes, we have assigned the new mutation to the alpha 2 gene. Position 72 of the alpha chain is a moderately conserved site located between two non-conserved amino acids. This site is not involved in heme, dimer or tetramer contacts, or in Bohr effect or in 2,3-diphosphoglycerate binding.

A novel polyadenylation signal mutation in the alpha 2-globin gene causing alpha thalassaemia

In a family of Indian origin we have identified a deletion of two bases at the polyadenylation signal sequence of the alpha 2-globin gene (AATAAA-->AATA). Three individuals heterozygous for this mutation display an alpha o-thalassaemia-like phenotype. Single-stranded conformation analysis and automatic sequencing showed no additional mutations in either alpha 1- or alpha 2-globin genes. A previously described polyadenylation sequence mutation (AATAAA-->AATAAG), alpha TSaudi alpha, causes HbH disease in homozygotes. In this study the patients heterozygous for the AATA(-AA) mutation show a similar phenotype observed in the alpha TSaudi alpha heterozygotes. This confirms the observation that the inefficient transcriptional termination due to mutations of the polyadenylation sequence of the alpha 2-gene might interfere with the alpha 1-gene expression.

Hb Kurdistan [alpha 47(CE5)Asp-->Tyr], a new alpha chain variant in combination with beta (0)-thalassemia

We have characterized the structural abnormality of a new alpha chain mutant found in a Kurdish family. The clinical and hematological investigation of eight individuals have shown that the alpha variant is associated with a beta(0)-thalassemia mutation (nonsense codon 39). The tryptic peptide map and sequencing of the abnormal peptide revealed the substitution of an aspartic acid by a tyrosine residue at position 47 of the alpha chain; furthermore, selective amplification and molecular analysis of both alpha genes have assigned the new mutation to the alpha 2 gene. The variant, named Hb Kurdistan, is clinically silent but the percentage of this hemoglobin found in the only double heterozygote for beta (0)-thalassemia and alpha-Kurdistan, presumably indicates a lower affinity of the abnormal chain for the beta polypeptides.

Homozygous beta+ thalassaemia owing to a mutation in the cleavage-polyadenylation sequence of the human beta globin gene

A mild, non-transfusion dependent, beta thalassaemia phenotype is described in a Dutch patient homozygous for a mutation in the cleavage-polyadenylation sequence of the beta globin gene. The molecular basis of the mutation, AATAAA greater than AATGAA, was determined using denaturing gradient gel electrophoresis (DGGE) and direct sequencing of genomic DNA amplified by the polymerase chain reaction (PCR). Different fragments of the beta globin gene were amplified and analysed on DGGE for the presence of mutations. The fragment with an abnormal melting behaviour was reamplified and the base substitution in the polyadenylation sequence was identified by direct sequencing.

Multiple recombination events are responsible for the heterogeneity of alpha(+)-thalassemia haplotypes among the forest tribes of Andhra Pradesh, India

The presence of several polymorphic markers along the alpha-globin gene complex allows the identification of haplotypes associated with alpha-thalassemia determinants. These are found at very high frequencies in geographic areas where malaria is or has been endemic which suggests a positive selective role by the parasitic disease in favour of alpha(+)-thalassemia mutants. A population survey among forest tribal communities from Andhra Pradesh, India, revealed the prevalence and molecular heterogeneity of alpha(+)-thalassemia determinants presumably due to a long backdated malaria endemicity among these populations. Analysis of the tribal alpha-thalassemia haplotypes has shown a great degree of genetic heterogeneity which can be explained as the result of multiple recombination events in the presence of natural selection by malaria.

Denaturing gradient gel electrophoresis and direct sequencing of PCR amplified genomic DNA: a rapid and reliable diagnostic approach to beta thalassaemia

The analysis of polymerase chain reaction (PCR)-amplified beta-globin DNA with allele-specific oligonucleotide (ASO) probes reveals a very heterogeneous spectrum of beta-thalassaemia in the Netherlands. However about 20% of the beta-thalassemia mutations cannot be identified with this approach. The combination of specific amplification of certain regions of the beta-globin gene with denaturing gradient gel electrophoresis (DGGE) allowed us to rapidly localize several of these mutations to specific regions of the gene, which were again amplified and directly sequenced. We believe that the combination of DGGE and the direct sequence determination of PCR amplified genomic DNA represents a valid alternative to the 'ASO probes' approach, especially in countries where a very heterogeneous spectrum of beta-thalassaemia mutations occurs.

A new AvaII RFLP in the human alpha-globin gene cluster

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