Rapid detection of point mutations and polymorphisms of the alpha-globin genes by DGGE and SSCA

Clinical Classification, Screening and Diagnosis for Thalassemia

At present, thalassemia diseases are classified into transfusion-dependent thalassemia and non-transfusion-dependent thalassemia. This classification is based on the clinical severity of patients determining whether they do require regular blood transfusions to survive (transfusion-dependent thalassemia) or not (non-transfusion-dependent thalassemia). In addition to the previous terminology of "thalassemia major" or "thalassemia intermedia," this classification has embraced all other forms of thalassemia syndromes such as α-thalassemia, hemoglobin E/β-thalassemia and combined α- and β-thalassemias. Definitive diagnosis of thalassemia and hemoglobinopathies requires a comprehensive workup from complete blood count, hemoglobin analysis, and molecular studies to identify mutations of globin genes.

Incidence of haemoglobinopathies in Sicily: the impact of screening and prenatal diagnosis

BACKGROUND

Haemoglobinopathies are a major public health problem in Sicily: it was estimated a frequency of 1/245 couples are at risk of haemoglobinopathies. This paper reviews legislative actions, prevention activities, carrier screening, genetic counselling, foetal sampling and laboratory methodology analysis evolution reporting the results of 30 years of prevention actions to assess the efficiency of our preventative programme in the control of haemoglobinopathies in Sicily.

METHODS

This programme consisted principally of five phases: legislative actions, public awareness campaign, carrier screening, genetic counselling and prenatal diagnosis.

RESULTS

These programmes have been very effective, which we can see from a greater public awareness of thalassaemia and its prevention in the target population furthermore by a marked decline in the incidence of thalassaemia major and sickle cell anaemia from 1 in 245 live births in the absence of prevention to 1 in 2000, with a reduction in about 85%. The residual cases were because of a conscious choice by expecting parents in relation to improved life expectancy as well as improved quality of life of the affected patients.

CONCLUSION

The study suggests that public health authorities should act and invest in a similar programme for prevention of thalassaemia, as well as in relation to the increased survival of patients and the consequent organ complications.

Two novel α2 gene mutations causing altered amino acid sequences produce a mild (Hb Kinshasa, HBA2: c.428A > T) and severe (HBA2: c.342-345insCC) α-thalassemia phenotype

We describe two novel α2 gene mutations that result in an altered amino acid sequence. In case 1, the α2 stop codon was mutated from TAA > TTA (HBA2: c.428A > T), resulting in an α2 protein chain extension of 31 amino acids. The new hemoglobin (Hb) variant was named Hb Kinshasa for the place of origin of the patient. This patient was also a carrier of Hb S (HBB: c.20A > T), which was expressed at reduced levels, but had an otherwise normal blood count. For cases 2 and 3, an α2 frameshift mutation caused a premature α2 protein chain termination at position 133 (HBA2: c.342-345insCC). The phenotype of this mutation seems to be rather severe as judged by the pronounced microcytosis and hypochromia observed in case 2. In addition, the father of this patient (case 3) also carried a β(0)-thalassemia (β(0)-thal) mutation (HBB: c.118C > T).

Advances in detection of hemoglobinopathies

Hemoglobin disorders are recognized as one of the most common inherited diseases worldwide. Detecting and characterizing variant hemoglobins and thalassemias depends primarily on clinical laboratory methods. Multiple biophysical, biochemical, and genetic assays are available to provide phenotypic or genotypic evidence of pathology. For many years conventional slab-gel electrophoresis and HPLC were the most commonly utilized laboratory methods. However, the field has rapidly expanded to regularly include capillary zone electrophoresis, molecular assays, and, more recently, mass spectrometric assays. Interpretation of these techniques is, in general, complicated because of the involvement of multiple polymorphic genes. Proper characterization of hemoglobin variants is necessary for diagnosis, primary prevention and genetic counseling for underlying disorders. This review provides an overview of the current hemoglobin analysis techniques, and also discusses technologies that have potential to translate into widespread clinical settings.

Prenatal Diagnosis of Hemoglobinopathies: From Fetoscopy to Coelocentesis

Prenatal diagnosis of hemoglobinopathies involves the study of fetal material from blood, amniocytes, trophoblast coelomatic cells and fetal DNA in maternal circulation. Its first application dates back to the 70s and it involves globin chain synthesis analysis on fetal blood. In the 1980s molecular analysis was introduced as well as amniocentesis and chorionic villi sampling under high-resolution ultrasound imaging. The application of direct sequencing and polymerase chain reactionbased methodologies improved the DNA analysis procedures and reduced the sampling age for invasive prenatal diagnosis from 18 to 16–11 weeks allowing fetal genotyping within the first trimester of pregnancy. In the last years, fetal material obtained at 7–8 weeks of gestation by coelocentesis and isolation of fetal cells has provided new platforms on which to develop diagnostic capabilities while non-invasive technologies using fetal DNA in maternal circulation are starting to develop.

EMQN Best Practice Guidelines for molecular and haematology methods for carrier identification and prenatal diagnosis of the haemoglobinopathies

Haemoglobinopathies constitute the commonest recessive monogenic disorders worldwide, and the treatment of affected individuals presents a substantial global disease burden. Carrier identification and prenatal diagnosis represent valuable procedures that identify couples at risk for having affected children, so that they can be offered options to have healthy offspring. Molecular diagnosis facilitates prenatal diagnosis and definitive diagnosis of carriers and patients (especially ‘atypical' cases who often have complex genotype interactions). However, the haemoglobin disorders are unique among all genetic diseases in that identification of carriers is preferable by haematological (biochemical) tests rather than DNA analysis. These Best Practice guidelines offer an overview of recommended strategies and methods for carrier identification and prenatal diagnosis of haemoglobinopathies, and emphasize the importance of appropriately applying and interpreting haematological tests in supporting the optimum application and evaluation of globin gene DNA analysis.

Homozygous Hb Stanleyville-II [alpha2 78(EF7) Asn>Lys; HBA2:c.237C>A, not C>G] associated with genotype -α 3.7/-α 3.7 in two Brazilian families

INTRODUCTION

Several hemoglobin variants have electrophoretic behavior similar to hemoglobin S, which may lead to false diagnosis for sickle-cell disorders in newborn screening programs. A homozygous hemoglobin with S mobility was detected in two unrelated babies in Brazil.

METHODS

Isoelectric focusing and high-performance liquid chromatography assays, gene sequencing, and restriction fragment length polymorphism with AfeI were used to characterize the hemoglobin.

RESULTS

Hb Stanleyville-II and -α(3.7) /-α(3.7) type I deletion in the α-globin gene was diagnosed. Parents were heterozygous for both Hb Stanleyville-II and α-thalassemia. Hypochromia and microcytosis were probably due to the homozygous α-thalassemia.

CONCLUSION

Stanleyville-II gene mutation is HBA2:c.237C>A, or C>G, and this information on the Globin Gene Server should be updated; AfeI test is a fast and accurate method to detect it; NBS programs should consider the possibility of Hb Stanleyville-II whenever IEF shows one band in the HbS position, and another one between S and C.

A New Highly Unstable α Chain Variant Causing α+‐Thalassemia: Hb Zurich Albisrieden [α59(E8)Gly→Arg (α2)]

A new alpha-globin mutation causing persistent mild hypochromic microcytosis and erythrocytosis is described. Hb Zurich Albisrieden [alpha59(E8)Gly-->Arg (alpha2)] is not detected at the protein level and leads to alpha(+)-thalassemia (thal).

A Novel α‐Thalassemia Nonsense Mutation in Codon 23 of the α2‐Globin Gene (GAG→TAG) in a Tunisian Family

Herein we describe a novel alpha-thalassemia (thal) point mutation in the alpha2-globin gene, found in a 3-year-old Tunisian girl who had Hb Bart's (gamma4) at birth, later on presenting with moderate anemia, microcytosis and hypochromia. She had a normal Hb A2 level and no abnormal hemoglobin (Hb) fraction. After excluding most of the common Mediterranean mutations, the alpha2-globin gene was sequenced and found to have a point mutation in the heterozygous state that creates a premature stop signal for translation (GAG-->TAG or Glu-->Term) at codon 23. The same mutation was also found in the mother in the heterozygous state, while the father had a normal sequence. The presence of the mutation was also confirmed by nucleotide sequencing of the opposite strand. Since the mutation creates a restriction site for the BfaI enzyme, a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based assay was established for screening purposes.

First Description in Tunisia of a Point Mutation at Codon 119 (CCT→TCT) in the α1-Globin Gene: Hb Groene Hart in Association with the − α3.7Deletion

Herein we describe the case of a Tunisian girl who presented with 3% Hb Bart's (gamma4) at birth. At the age of 3 years, she showed microcytosis and hypochromia in the absence of iron deficiency. The first step of molecular analysis was to test for the common Mediterranean mutations and the classical -alpha3.7 deletion was found in the heterozygous state. Since this finding could not explain the level of Hb Bart's at birth, or the hypochromia and microcytosis, all the alpha-globin genes were sequenced. This revealed a rare point mutation at codon 119 (CCT-->TCT) in the alpha1-globin gene, identified for the first time in Tunisia, and which has previously been described as an unstable hemoglobin (Hb) variant named Hb Groene Hart [alpha119(H2)Pro-->Ser (alpha1)]. Here the -alpha3.7/alpha(alpha)119(CCT-->TCT) genotype is responsible for the alpha-thalassemia (thal) trait phenotype.

Hb Bleuland [α108(G15)Thr→Asn, ACC→AAC (α2)]: A New Abnormal Hemoglobin Associated with a Mild α-Thalassemia Phenotype

We report a new structural defect of the alpha2-globin chain, not detectable on high performance liquid chromatography (HPLC) or electrophoresis, characterized in a 12-year-old boy of Surinamese-Hindustani origin. The child was suspected to be a carrier of alpha-thalassemia (thal) because of microcytic hypochromic parameters in the absence of iron depletion. Gap-polymerase chain reaction (gap-PCR) revealed only normal fragments in the proband, and the pattern of a -alpha4.2 (leftward) deletion in his father and sister. Direct sequencing of the alpha-globin genes revealed an ACC-->AAC transversion at codon 108 of the alpha2-globin gene in the proband, in his mother and in a younger sister. The new mutation predicts a Thr -->Asn amino acid substitution at the corresponding residue. Threonine, a covalent binder with an R-active OH group, situated in the G helix of the alpha-globin chain, is involved in alpha1beta1 contacts. Asparagine, being an equally covalent binder but with a different R-active H2N-C=O group, could make the mutated chain less suitable for tetramer cooperation. Alternatively, an absent or reduced interaction with the alpha hemoglobin (Hb) stabilizing protein (AHSP) could lead to loss of alpha chains. Hb Bleuland is the first mutation described at codon 108 and is therefore interesting in regard to the possible effects and genetic risk. The nearest variant, Hb Suan-Dok [alpha109(G16)Leu -->Arg, CTG-->CGG (alpha2)] was originally observed in a Thai patient affected with Hb H, in combination with an alpha0-thal allele. The same Hb Suan-Dok mutation, recently described in our laboratory in a carrier of African ancestry, was also not detectable as a protein and presented with an alpha-thal phenotype similar to Hb Bleuland.

Detection and haplotype differentiation of Southeast Asian alpha-thalassemia using polymerase chain reaction and a piezoelectric biosensor immobilized with a single oligonucleotide probe

DNA-based diagnosis of alpha-thalassemias routinely relies on polymerase chain reaction (PCR) and gel electrophoresis. Here, we developed a new procedure for the detection and haplotype differentiation of Southeast Asian (SEA) alpha-thalassemia using a 3-primer system for PCR coupling with a DNA-based piezoelectric biosensor. PCR products amplified from genomic DNA were differentiated directly by using a quartz crystal microbalance immobilized with a single oligonucleotide probe. The frequency changes after hybridization of the PCR products amplified from a representative sample of normal alpha-globin, SEA alpha-thalassemia heterozygote, and homozygote were 206+/-11, 256+/-5, and 307+/-3 Hz, respectively. The fabricated biosensor was evaluated through an examination of 18 blind specimens. It could accurately discriminate between normal and SEA alpha-thalassemic samples, which suggests that this biosensor system is a promising alternative technique to detect SEA alpha-thalassemia because of its specificity and less hazardous exposure as compared with conventional methods.

Screening and genetic diagnosis of haemoglobinopathies

The haemoglobin disorders are a group of autosomal recessive disorders characterized by either the reduced synthesis of one or more normal globin chains (the thalassaemias), the synthesis of a structurally abnormal globin chain (the haemoglobin variants) or in a few cases by both phenotypes (the reduced synthesis of a Hb variant, e.g. Hb E). They are the commonest single-gene disorders known and approximately 1000 different mutant alleles have now been characterized at the molecular level. The mutations are regionally specific, with each country having its own unique spectrum of abnormal haemoglobins and thalassaemia mutations, and can occur at high gene frequencies in some ethnic groups 1. Although haemoglobinopathy mutations are rarely found in individuals of North European origin, the number of immigrants in the North European countries is steadily increasing and the variety of their ethnic origins poses a problem for screening and accurate diagnosis.

Microsatellite Markers within —SEA Breakpoints for Prenatal Diagnosis of HbBarts Hydrops Fetalis

Background: We sought to develop a rapid prenatal diagnostic test for simultaneous detection of HbBarts hydrops fetalis and exclusion of maternal contamination.

Methods: We developed a multiplex quantitative fluorescent PCR (QF-PCR) test that detects the presence/ absence of 2 microsatellite markers (16PTEL05/16PTEL06) located within breakpoints of the Southeast Asia (—SEA) deletion. HbBarts hydrops fetalis (—SEA/—SEA) is diagnosed by absence of both markers, and maternal contamination of fetal DNA is excluded by absence of noninherited maternal alleles. Fetal and parental DNA samples from 50 families were analyzed in a blinded clinical validation study, and QF-PCR results were compared with their respective molecular genotypes.

Results: The multiplex QF-PCR results included correct diagnoses of HbBarts hydrops fetalis in 11 of the fetuses tested, correct verification as unaffected in 20 fetuses, and correct identification as either carriers (αα/—SEA) or unaffected homozygotes in 18. Misidentification as unaffected occurred for 1 carrier. Sensitivity for diagnosis of HbBarts hydrops fetalis was 100% [lower 95% confidence interval, 76.2%], and specificity was 100% (lower 95% confidence interval, 92.6%). None of the samples tested showed any traces of noninherited maternal alleles; thus false-positives because of maternal contamination were eliminated.

Conclusions: In this QF-PCR method, detection of maternally and paternally inherited fetal alleles allowed diagnosis of the double-deletion syndrome, and the ability to differentiate between these alleles allowed simultaneous exclusion of maternal contamination of the fetal genetic material. This novel strategy using cell-free fetal DNA in maternal plasma could form the basis for noninvasive testing for HbBarts hydrops fetalis.

Hb Amsterdam [alpha32(B13)Met--Ile (alpha2)]: a new unstable variant associated with an alpha-thalassemia phenotype and a new African polymorphism

We have characterized a new abnormal hemoglobin (Hb) at position 32 of the alpha-globin chain. The proband, a 38-year-old woman of Surinamese Black ancestry, was referred to the Academic Hospital in Amsterdam, The Netherlands, after 3 years of Prednisone treatment in Surinam. Kidney failure was diagnosed at the Nephrology Department, Free University Medical Center, Amsterdam, The Netherlands; the cortisone treatment was interrupted and dialysis was started. At this stage, a microcytic hypochromic anemia was observed with high reticulocyte (40%) and ferritin (500 microg/L) levels, and hemoglobinopathy was suspected. No abnormal bands were visible on alkaline electrophoresis and high performance liquid chromatography (HPLC). The Hb A2 level was normal (2.7%) and the erythrocyte count was low (3.59 x 10(12)/L) with a normal haptoglobin level (68 mg/100 mL). None of the common alpha-thalassemia (thal) deletion defects were present. The beta-globin gene sequence was normal but the alpha2-globin gene sequence revealed an ATG-->ATA transition at codon 32, changing the methionine into an isoleucine residue. The mutation, called Hb Amsterdam, was observed in the mother of the proband, who was also heterozygous for the--alpha3.7-thal deletion and affected by a moderate microcytic hypochromic anemia. Both Hb Amsterdam and the--alpha(-3.7) allele were found in association with a new polymorphism, IVS-I-39 (C-->T), previously observed in our laboratory in seven patients of African origin, on both the alpha1 and alpha2 genes. In addition, Hb Amsterdam was also associated with the common African alpha2 polymorphism (G-->CTCGGCCC at position 7238 and T-->G at position 7174). Hb Amsterdam is the first mutation ever described at codon alpha32, a position involved in alpha1/beta1 interaction. The possibility of a contribution of this mutation to the nephropatic state of the proband is discussed.

Hb Oegstgeest [alpha104(G11)Cys-->Ser (alpha1)]. A new hemoglobin variant associated with a mild alpha-thalassemia phenotype

A microcytic hypochromic anemic state was observed in an 8-year old Black female of Surinam origin during pre-operative Hb S [beta6(A3)Glu-->Val] screening. Her high zinc protoporphyrin (ZPP) level suggested a chronic iron depletion but, in contrast, the high red blood cell (RBC) count (5.85 x 10(12)/L) was indicative of a possible coexisting thalassemia. No abnormal hemoglobin (Hb) bands were present on high performance liquid chromatography (HPLC) or alkaline electrophoresis and the Hb A2 level was normal. Break point polymerase chain reaction (PCR) failed to reveal any of the common alpha-thalassemia (thal) mutations but selective DNA sequencing of both alpha-globin genes disclosed a TGC-->AGC transversion at codon 104 of the alpha1 gene. Cystine at codon 104 is involved in alpha/beta globin contact and has been described to be a critical amino acid of the alpha2 chain when substituted by a tyrosine (Hb Sallanches), inducing Hb H (beta4) disease in the homozygous state. Our heterozygous patient had a moderate anemia of 12.2 g/dL and a borderline haptoglobin suggesting some degree of hemolysis.

Molecular diagnosis of inherited disorders: lessons from hemoglobinopathies

Hemoglobinopathies constitute a major health problem worldwide, with a high carrier frequency, particularly in certain regions where malaria has been endemic. These disorders are characterized by a vast clinical and hematological phenotypic heterogeneity. Over 1,200 different genetic alterations that affect the DNA sequence of the human alpha-like (HBZ, HBA2, HBA1, and HBQ1) and beta-like (HBE1, HBG2, HBG1, HBD, and HBB) globin genes are mainly responsible for the observed clinical heterogeneity. These mutations, together with detailed information about the resulting phenotype, are documented in the globin locus-specific HbVar database. Family studies and comprehensive hematological analyses provide useful insights for accurately diagnosing thalassemia at the DNA level. For this purpose, numerous techniques can provide accurate, rapid, and cost-effective identification of the underlying genetic defect in affected individuals. The aim of this article is to review the diverse methodological and technical platforms available for the molecular diagnosis of inherited disorders, using thalassemia and hemoglobinopathies as a model. This article also attempts to shed light on issues closely related to thalassemia diagnostics, such as prenatal and preimplantation genetic diagnoses and genetic counseling, for better-quality disease management.

Sequence variations of the ?-globin genes: Scanning of high CG content genes with DHPLC and DG-DGGE

The alpha-globin chains are encoded by two duplicated genes (HBA2 and HBA1, 5'-3') showing overall sequence homology >96% and average CG content >60%. alpha-Thalassemia, the most prevalent worldwide autosomal recessive disorder, is a hereditary anemia caused by sequence variations of these genes in about 25% of carriers. We evaluated the overall sensitivity and suitability of DHPLC and DG-DGGE in scanning both the alpha-globin genes by carrying out a retrospective analysis of 19 variant alleles in 29 genotypes. The HBA2 alleles c.1A>G, c.79G>A, and c.281T>G, and the HBA1 allele c.475C>A were new. Three pathogenic sequence variations were associated in cis with nonpathogenic variations in all families studied; they were the HBA2 variation c.2T>C associated with c.-24C>G, and the HBA2 variations c.391G>C and c.427T>C, both associated with c.565G>A. We set up original experimental conditions for DHPLC and DG-DGGE and analyzed 10 normal subjects, 46 heterozygotes, seven homozygotes, seven compound heterozygotes, and six compound heterozygotes for a hybrid gene. Both the methodologies gave reproducible results and no false-positive was detected. DHPLC showed 100% sensitivity and DG-DGGE nearly 90%. About 100% of the sequence from the cap site to the polyA addition site could be scanned by DHPLC, about 87% by DG-DGGE. It is noteworthy that the three most common pathogenic sequence variations (HBA2 alleles c.2T>C, c.95+2_95+6del, and c.523A>G) were unambiguously detected by both the methodologies. Genotype diagnosis must be confirmed with PCR sequencing of single amplicons or with an allele-specific method. This study can be helpful for scanning genes with high CG content and offers a model suitable for duplicated genes with high homology.

Determination of the breakpoint and molecular diagnosis of a common α-thalassaemia-1 deletion in the Indian population

The previously described South African type alpha-thalassaemia-1 mutation was identified in Indian HbH patients using a polymerase chain reaction (PCR) strategy. A multiplex PCR assay was devised to detect heterozygotes and homozygotes. This alpha-thalassaemia-1 mutation was found to be the commonest determinant causing HbH disease in this population. In one family this mutation was found in combination with a novel splice donor mutation alpha2 IVS I-1 (G-->A). Characterization of the breakpoint junction sequence revealed, in addition to a 23 kb deletion, that there was an addition of approximately 160 bp bridging the breakpoints. Similar to other deletions in the alpha-globin gene cluster, there is an Alu repeat-mediated mechanism for the origin of the deletion.

Screening for mutations in human alpha-globin genes by nonradioactive single-strand conformation polymorphism

Point mutations and small insertions or deletions in the human alpha-globin genes may produce alpha-chain structural variants and alpha-thalassemia. Mutations can be detected either by direct DNA sequencing or by screening methods, which select the mutated exon for sequencing. Although small (about 1 kb, 3 exons and 2 introns), the alpha-globin genes are duplicate (alpha2 and alpha1) and highly G-C rich, which makes them difficult to denature, reducing sequencing efficiency and causing frequent artifacts. We modified some conditions for PCR and electrophoresis in order to detect mutations in these genes employing nonradioactive single-strand conformation polymorphism (SSCP). Primers previously described by other authors for radioactive SSCP and phast-SSCP plus denaturing gradient gel electrophoresis were here combined and the resultant fragments (6 new besides 6 original per alpha-gene) submitted to silver staining SSCP. Nine structural and one thalassemic mutations were tested, under different conditions including two electrophoretic apparatus (PhastSystem and GenePhor, Amersham Biosciences), different polyacrylamide gel concentrations, run temperatures and denaturing agents, and entire and restriction enzyme cut fragments. One hundred percent of sensitivity was achieved with four of the new fragments formed, using the PhastSystem and 20% gels at 15 degree C, without the need of restriction enzymes. This nonradioactive PCR-SSCP approach showed to be simple, rapid and sensitive, reducing the costs involved in frequent sequencing repetitions and increasing the reliability of the results. It can be especially useful for laboratories which do not have an automated sequencer.

Screening and genetic diagnosis of haemoglobin disorders

The inherited haemoglobinopathies are large group of disorders that include the thalassaemias and sickle cell disease. Carrier detection methods must be able to detect alpha-, beta- and deltabeta-thalassaemias, HPFH disorders and haemoglobin variants. Carrier diagnosis involves the accurate measurement of MCH, MCV, Hb A(2) and Hb F values in combination with an understanding of the haematological characteristics of the different types of thalassaemia genes and their interactions. The majority of the common thalassaemia mutations and abnormal haemoglobins can be identified by PCR-based techniques. The main applications of molecular analysis for carrier diagnosis are: the analysis of alpha-thalassaemia mutations by gap-PCR to discriminate between heterozygous alpha-thalassaemia and homozygous alpha-thalassaemia; the identification of beta-thalassaemia mutations for patients requiring prenatal diagnosis and for the prediction of the severity of the clinical phenotype of homozygous beta-thalassaemia; to discriminate between deltabeta-thalassaemia and HPFH deletions by gap-PCR.

A novel 7.9 kb deletion causing alpha+-thalassaemia in two independent families of Indian origin

We describe the characterization of a novel 7.9 kb deletion that eliminated one of the duplicated alpha-globin genes, causing an alpha+-thalassaemia phenotype in two independent carriers of Suriname-Indian origin. The molecular characterization of the deletion breakpoint fragment revealed neither involvement of Alu repeat sequences nor the presence of homologous regions prone to recombination, suggesting a non-homologous recombination event. This alpha+-thalassaemia deletion was found to give rise to an atypical haemoglobin H (HbH) disease characterized by a non-transfusion-dependent moderate microcytic hypochromic anaemia in combination with a poly adenylation signal mutation of the alpha-globin gene (alpha2 AATAAA --> AATA-- --).

Molecular spectrum of alpha-thalassemia in Tunisia: epidemiology and detection at birth

We present the characterization of the molecular spectrum and frequency data of alpha-thal (thal) defects in Tunisia, and an evaluation of the efficacy and limitations of Hb Bart's (gamma4) measurement for the screening of alpha-thal at birth. Cord blood samples were collected from two different areas: the northeast of the country, an area where Hb H (beta4) disease frequently occurs, and Tunis, the capital city, representative of the average Tunisian population. From the first group, 110 samples with Hb Bart's and/or microcytosis at birth were selected from 1270 randomly collected samples. Two additional population samples, one from the same northeastern region (n = 90), the other from Tunis (n = 104) were collected randomly. Nine common deletional alpha-thal defects and nondeletional mutations were screened. In the northeastern samples, selected for the presence of Hb Bart's and microcytosis, the -alpha3.7 deletion was the most common defect (4.5% allele frequency) followed by a polyadenylation (poly A) signal mutation (1.8%), the five nucleotide (nt) deletion and the -alpha4.2 deletion (both 0.9%). The African polymorphism (G-->TCGGCCC at position 7238 and T-->G at 7174) was found with an allele frequency of 11% in the selected northeastern samples. In the random population samples, the overall alpha-thal allele frequency was 4% in the northeast region, against 2% in the average Tunisian population. The +14 (G-->C) polymorphism in the 5'UTR (untranslated region) of the alpha2 gene and the African polymorphism in the second intron of the same gene, were found in 3.5% of the alleles. No alpha0-thal alleles were found among the 304 blood samples studied at the DNA level during this survey.

Detection of a novel variant human hemoglobin by electrospray ionization mass spectrometry

A novel hemoglobin variant was detected by electrospray ionization mass spectrometry. Hb Zurich-Hottingen is characterized by an Asn --> Ser replacement in the alpha-chain at position 9 as confirmed by DNA analysis. This hemoglobin variant is silent in isoelectric focusing, reversed-phase chromatography, and cation-exchange chromatography. The mutant alpha-chain was detectable only with electrospray mass spectrometry by its mass shift of -27 Da. The carrier was found to be heterozygous for the new hemoglobin variant. These results illustrate the power of ESI mass spectrometry for hemoglobin analysis.

Hb Dartmouth [alpha66(E15)Leu-->Pro (alpha2) (CTG-->CCG)]: a novel alpha2-globin gene mutation associated with severe neonatal anemia when inherited in trans with Southeast Asian alpha-thalassemia-1

We report a novel mutation at alpha66(E15)Leu-->Pro (alpha2) (CTG-->CCG), that we have named Hb Dartmouth for the medical center at which the patients were cared for, in monozygotic twins who also inherited the Southeast Asian alpha-thalassemia-1 deletion. The mother, of Khmer ancestry, is heterozygous for alpha-thalassemia-1. The father, who is of Scottish-Irish ancestry, is a silent carrier of the codon 66 mutation. The twins had severe neonatal anemia requiring transfusion.

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.

Interaction of an alpha(+)-thalassemia deletion with either a highly unstable alpha-globin variant (alpha2, codon 59, GGC-->GAC) or a nondeletional alpha-thalassemia mutation (AATAAA-->AATAAG): comparison of phenotypes illustrating "dominant" alpha-thalassemia

Thalassemia syndromes and unstable hemoglobins traditionally represent two phenotypically separate disorders of hemoglobin synthesis. Highly unstable hemoglobin variants, however, often have phenotypic characteristics associated with both ineffective erythropoiesis (thalassemias) and peripheral hemolysis (unstable hemoglobins). Many highly unstable beta chain variants cause a dominant thalassemia-like phenotype, in which simple heterozygotes for such mutations have a clinical expression similar to thalassemia intermedia. The phenotypic expression of highly unstable alpha-globin variants is usually less severe, due mainly to a gene dosage effect, and they are often only characterized on interaction with other alpha-thalassemia mutations, whence they are classified as nondeletional alpha-thalassemia determinants. This study reports the clinical and hematological findings in five cases with rare alpha-thalassemia genotypes: a single patient with the thalassemic alpha2-globin gene codon 59 Gly-->Asp hemoglobin variant in trans to an alpha(+)-thalassemia deletion, and four compound heterozygotes for the nondeletional alpha-thalassemia polyadenylation mutation (alpha2 gene AATAAA-->AATAAG or alpha(T-Saudi)alpha/-alpha) and an alpha(+)-thalassemia deletion. Evaluation of the clinical and hematological features in these two analogous genotypes clearly demonstrates the more severe clinical expression associated with the alpha-thalassemic unstable hemoglobin variant. In addition, the case in this study with the codon 59 alpha chain variant provides a further example illustrating the spectrum of phenotypes associated with the alpha-thalassemic hemoglobinopathies.

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

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

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.