Beta-thalassaemia in the immigrant and non-immigrant German populations

Splice Acceptor Mutation [HBB:c.93-2A > T] in a Patient with Hb S/β0-Thalassemia

We report a case of Hb S/β0-thalassemia (Hb S/β0-thal) in a patient who is a compound heterozygote for the Hb Sickle mutation (HBB:c.20A > T) and a mutation of the canonical splice acceptor sequence of IVS1 (AG > TG, HBB:c.93-2A > T). This is the fifth mutation involving the AG splice acceptor site of IVS1, all of which prevent normal splicing and cause β0-thal.

A large cohort of deletional high hemoglobin F determinants in Thailand: A molecular revisited and identification of a novel mutation

BACKGROUND AND AIMS

High hemoglobin F determinants can be classified into hereditary persistence of fetal hemoglobin (HPFH) and δβ-thalassemia with different phenotype. We report the molecular basis and hematological features in a large cohort of deletional high Hb F determinants in Thailand.

MATERIALS AND METHODS

Subjects (n = 28,177) encountered during 2015-2022 were reviewed, and those with phenotypically suspected of having high Hb F determinants were selected. Combined PCR, multiplex ligation-dependent probe amplification, next-generation sequencing, and DNA sequencing were used to identify the mutations.

RESULTS

Among 28,177 subjects investigated, 300 (1.06 %) were found to carry deletional high Hb F determinants in a total of 302 alleles, including heterozygote, compound heterozygote with β-hemoglobinopathies, and homozygote. DNA analysis identified eight different DNA deletions, including δβ0-thalassemia (12.6 kb deletion) (73.8 %), HPFH-6 (14.9 %), Indian deletion-inversion Aγδβ0-thalassemia (3.6 %), Thai deletion-inversion-insertion Aγδβ0-thalassemia (3.0 %), SEA-HPFH (3.0 %), Chinese Aγδβ0-thalassemia (1.0 %), Thai δβ0-thalassemia (11.3 kb deletion) (0.3 %), and a novel δβ0-thalassemia (137.1 kb deletion) (0.3 %). In addition, three novel genetic interactions, including Chinese Aγδβ0-thalassemia/Hb E, δβ0-thalassemia/Indian deletion-inversion Aγδβ0-thalassemia, and homozygous δβ0-thalassemia were found. Hematological features and Hb analysis results of 20 different genotypes were recorded. Multiplex gap-PCR assays for detection of these genetic determinants were described.

CONCLUSIONS

Deletional high Hb F determinants are common and heterogeneous in Thailand. Data on the prevalence, molecular spectrum, phenotypic expression, and complex interactions of these genetic determinants should prove useful in the study and a prevention and control program of hemoglobinopathies in the region.

The beta thalassaemia trait in Jamaica

The objective of this study was to review the prevalence and features of the beta thalassaemia trait in Jamaican populations. Screening of 221,306 newborns over the last 46 years has given an indication of the distribution and prevalence of beta thalassaemia genes, and screening of 16,612 senior school students in Manchester parish, central Jamaica, has provided their haematological features. The prevalence of the beta thalassaemia trait predicted from double heterozygotes was 0.8% of 100,000 babies in Kingston, 0.9% of 121,306 newborns in southwest Jamaica, and 0.9% of school students in Manchester. Mild beta+ thalassaemia variants (-88 C>T, -29 A>G, -90 C>T, polyA T>C) accounted for 75% of Kingston newborns, 76% of newborns in southwest Jamaica, and 89% of Manchester students. Severe beta+ thalassaemia variants were uncommon. Betao thalassaemia variants occurred in 43 patients and resulted from 11 different variants of which the IVSII-849 A>G accounted for 25 (58%) subjects. Red cell indices in IVSII-781 C>G did not differ significantly from HbAA, and this is probably a harmless polymorphism rather than a form of beta+ thalassaemia; the removal of 6 cases in school screening had a minimal effect on the frequency of the beta thalassaemia trait. Red cell indices in the beta+ and betao thalassaemia traits followed established patterns, although both were associated with increased HbF levels. The benign nature of beta+ thalassaemia genes in Jamaica means that cases of sickle cell-beta+ thalassaemia are likely to be overlooked, and important clinical questions such as the role of pneumococcal prophylaxis remain to be answered.

Newborn screening for abnormal haemoglobins in Jamaica: Practical issues in an island programme

OBJECTIVE

To report the diagnostic challenges of newborn screening for abnormal haemoglobins.

SETTING

Cord blood samples from 13 hospitals in southwest Jamaica taken in 2008-2019.

METHODS

Blood spots, collected from the umbilical cord, were analysed by high pressure liquid chromatography (HPLC) to reveal phenotypes for HbSS and HbCC, but genotype confirmation may require parental studies or gene sequencing. Such cases that were successfully traced were analysed in this follow-up study.

RESULTS

HPLC screening of 121,306 samples detected HbAS in 11,846 (9.8%), HbAC in 4508 (3.7%) and other electrophoretic abnormalities in 1090 babies. Among 101 previously unconfirmed cases, 34/90 (38%) with HPLC evidence of a HbSS phenotype had other genotypes, and 7/11 (64%) with a HbCC phenotype had other genotypes. Syndromes from the interaction of β thalassaemia occurred in 112 babies (85 with HbS, 27 with HbC) and of genes for hereditary persistence of fetal haemoglobin (HPFH) in 18 (12 with HbS, 6 with HbC). Variants other than HbS and HbC occurred in 270 babies, 16 in combination with either HbS or HbC, and 254 as traits. Most variants are benign even when inherited with HbS, although HbO Arab, HbD Punjab, or Hb Lepore Washington, which occurred in 6 cases, may cause sickle cell disease.

CONCLUSIONS

Genes for β thalassaemia and HPFH are common in western Jamaica and when associated with HbS may present diagnostic challenges in newborns, as HbF and HbA₂ have not reached diagnostic levels. Family and DNA studies may be necessary for genotype confirmation.

Hb S/-Thalassemia in the REDS-III Brazil Sickle Cell Disease Cohort: Clinical, Laboratory and Molecular Characteristics

We described the clinical, laboratory and molecular characteristics of individuals with Hb S (HBB: c.20A>T)/β-thalassemia (Hb S/β-thal) participating in the Recipient Epidemiology and Donor Evaluation Study (REDS-III) Brazil Sickle Cell Disease cohort. HBB gene sequencing was performed to genotype each β-thal mutation. Patients were classified as Hb S/β⁰-thal, Hb S/β⁺-thal-severe or Hb S/β⁺-thal based on prior literature and databases of hemoglobin (Hb) variants. Characteristics of patients with each β-thal mutation were described and the clinical profile of patients grouped into Hb S/β⁰-thal, Hb S/β⁺-thal and Hb S/β⁺-thal-severe were compared. Of the 2793 patients enrolled, 84 (3.0%) had Hb S/β⁰-thal and 83 (3.0%) had Hb S/β⁺-thal; 40/83 (48.2%) patients with Hb S/β⁺-thal had mutations defined as severe. We identified 19 different β-thal mutations, eight Hb S/β⁰-thal, three Hb S/β⁺-thal-severe and eight Hb S/β⁺-thal. The most frequent β⁰ and β⁺ mutations were codon 39 (HBB: c.118C>T) and IVS-I-6 (T>C) (HBB: c.92+6T>C), respectively. Individuals with Hb S/β⁰-thal had a similar clinical and laboratory phenotype when compared to those with Hb S/β⁺-thal-severe. Individuals with Hb S/β⁺-thal-severe had significantly lower total Hb and Hb A levels and higher Hb S, white blood cell (WBC) count, platelets and hemolysis markers when compared to those with Hb S/β⁺-thal. Likewise, individuals with Hb S/β⁺-thal-severe showed a significantly higher occurrence of hospitalizations, vaso-occlusive events (VOE), acute chest syndrome (ACS), splenic sequestration, blood utilization, and hydroxyurea (HU) therapy.

Mutation Spectrum of the ABCA4 Gene in a Greek Cohort with Stargardt Disease: Identification of Novel Mutations and Evidence of Three Prevalent Mutated Alleles

Aim

To evaluate the frequency and pattern of disease-associated mutations of ABCA4 gene among Greek patients with presumed Stargardt disease (STGD1).

Materials and Methods

A total of 59 patients were analyzed for ABCA4 mutations using the ABCR400 microarray and PCR-based sequencing of all coding exons and flanking intronic regions. MLPA analysis as well as sequencing of two regions in introns 30 and 36 reported earlier to harbor deep intronic disease-associated variants was used in 4 selected cases.

Results

An overall detection rate of at least one mutant allele was achieved in 52 of the 59 patients (88.1%). Direct sequencing improved significantly the complete characterization rate, that is, identification of two mutations compared to the microarray analysis (93.1% versus 50%). In total, 40 distinct potentially disease-causing variants of the ABCA4 gene were detected, including six previously unreported potentially pathogenic variants. Among the disease-causing variants, in this cohort, the most frequent was c.5714+5G>A representing 16.1%, while p.Gly1961Glu and p.Leu541Pro represented 15.2% and 8.5%, respectively.

Conclusions

By using a combination of methods, we completely molecularly diagnosed 48 of the 59 patients studied. In addition, we identified six previously unreported, potentially pathogenic ABCA4 mutations.

New Bioinformatics-Based Discrimination Formulas for Differentiation of Thalassemia Traits From Iron Deficiency Anemia

Thalassemia traits (TTs) and iron deficiency anemia (IDA) are the most common disorders of hypochromic microcytic anemia (HMA). The present study aimed to differentiate TTs from IDA by analyzing discrimination formulas and provides comprehensive data of hemoglobin disorders prevalent in Pakistan. Among 12 published discrimination formulas, 6 formulas-MI, EF, G&K, RDWI, R, and HHI-were the most reliable to discriminate TTs from IDA. The failure cutoff values were improved by the random forest (RF) decision-tree approach. Moreover, the Shine and Lal (S&L) formula, which completely failed to discriminate IDA from TTs with original cutoff value (<1530), improved with the use of new proposed cutoff value (<1016) and was found to successfully discriminate all cases of TTs from those with IDA. In addition, 2 newly proposed formulas discriminated TTs from IDA more reliably than the original 12 formulas assessed. The proposed formulas could play a crucial role for clinicians to discriminate between TTs and IDA.

Prevalence of Thalassemia Traits and Iron Deficiency Anemia in Sindh, Pakistan

Among microcytic hypochromic anemias, the most common disorders are iron deficiency anemia and co-pathological conditions such as α- or β-thalassemia (α- or β-thal) traits. The aim of the present study was to determine the frequency and prevalence of iron deficiency anemia and α- or β-thal traits based on clinical laboratory data across different ethnic groups in five districts of Sindh Province, Pakistan. The present retrospective study analyzed 3 years (2012-2015) of encoded and unlinked clinical laboratory data, and identified 3030 microcytic hypochromic anemia cases. The data contained complete blood counts (CBCs) with smear morphology examinations, serum ferritin levels, and hemoglobin (Hb) electrophoreses. After reviewing the data, 994 confirmed subjects (iron deficiency anemia and α- and β-thal traits) were then selected for the present study. The prevalence of α- and β-thal traits was highest in Badin district (35.27%), while the prevalence of iron deficiency anemia was highest in Larkana district (30.73%). According to the ethnic-wise distribution, higher numbers of α- and β-thal trait cases were seen in the Sindhi ethnic group [375 (64.21%) and 283 (69.02%), respectively] than in the other ethnic groups. In addition, a higher distribution of β-thal trait cases was observed in the Sindhi ethnic group [n = 327 (56%)] in α- and β-thal cases overall. Findings from the present study strongly suggested that screening is important not only for β-thal trait but also other traits as well. However, careful monitoring of CBC parameters, including red blood cell (RBC) indices and morphology, along with clinical findings are essential to diagnose carrier cases, especially in high prevalence areas.

Confirmation of a founder effect in a Northern European population of a new β-globin variant: HBB:c.23_26dup (codons 8/9 (+AGAA))

β-Thalassemia is a genetic disease caused by a defect in the production of the β-like globin chain. More than 200 known different variants can lead to the disease and are mainly found in populations that have been exposed to malaria parasites. We recently described a duplication of four nucleotides in the first exon of β-globin gene in several families of patients living in Nord-Pas-de-Calais (France). Using the genotypes at 12 microsatellite markers surrounding the β-globin gene of four unrelated variant carriers plus an additional one recently discovered, we found that they shared a common haplotype indicating a founder effect that was estimated to have taken place 225 years ago (nine generations). In order to determine whether this variant arose in this region of Northern Europe or was introduced by migrants from regions of the world where thalassemia is endemic, we genotyped the first 4 unrelated variant carriers and 32 controls from Nord-Pas-de-Calais for 97 European ancestry informative markers (EAIMs). Using these EAIMs and comparing with population reference panels, we demonstrated that the variant carriers were very similar to the controls and were closer to North European populations than to South European or Middle-East populations. Rare β-thalassemia variants have already been described in patients sampled in non-endemic regions, but it is the first proof of a founder effect in Northern Europe.

Application of diagnostic methods and molecular diagnosis of hemoglobin disorders in Khuzestan province of Iran

BACKGROUND:

The hemoglobinopathies refer to a diverse group of inherited disorders characterized by a reduced synthesis of one or more globin chains (thalassemias) or the synthesis of structurally abnormal hemoglobin (Hb). The thalassemias often coexist with a variety of structural Hb variants giving rise to complex genotypes and an extremely wide spectrum of clinical and hematological phenotypes. Hematological and biochemical investigations and family studies provide essential clues to the different interactions and are fundamental to DNA diagnostics of the Hb disorders. Although DNA diagnostics have made a major impact on our understanding and detection of the hemoglobinopathies, DNA mutation testing should never be considered a shortcut or the test of first choice in the workup of a hemoglobinopathy.

MATERIALS AND METHODS:

A careful three-tier approach involving: (1) Full blood count (2) Special hematological tests, followed by (3) DNA mutation analysis, provides the most effective way in which to detect primary gene mutations as well as gene-gene interactions that can influence the overall phenotype. With the exception of a few rare deletions and rearrangements, the molecular lesions causing hemoglobinopathies are all identifiable by PCR-based techniques. Furthermore, each at-risk ethnic group has its own combination of common Hb variants and thalassemia mutations. In Iran, there are many different forms of α and β thalassemia. Increasingly, different Hb variants are being detected and their effects per se or in combination with the thalassemias, provide additional diagnostic challenges.

RESULTS:

We did step-by-step diagnosis workup in 800 patients with hemoglobinopathies who referred to Research center of Thalassemia and Hemoglobinopathies in Shafa Hospital of Ahwaz Joundishapour University of medical sciences, respectively. We detected 173 patients as iron deficiency anemia (IDA) and 627 individuals as thalassemic patients by use of different indices. We have successfully detected 75% (472/627) of the β-thalassemia mutations by using amplification refractory mutation system (ARMS) technique and 19% (130/627) of the β-thalassemia mutations by using Gap-PCR technique and 6% (25/627) as Hb variants by Hb electrophoresis technique. We did prenatal diagnosis (PND) for 176 couples which had background of thalassemia in first pregnancy. Result of PND diagnosis in the first trimester was 35% (62/176) affected fetus with β-thalassemia major and sickle cell disease that led to termination of the pregnancy.

CONCLUSION:

Almost all hemoglobinopathies can be detected with the current PCR-based assays with the exception of a few rare deletions. However, the molecular diagnostic service is still under development to try and meet the demands of the population it serves. In the short term, the current generation of instruments such as the capillary electrophoresis systems, has greatly simplified DNA sequence analysis.

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.

Hb S-β-thalassemia: molecular, hematological and clinical comparisons

Clinical and hematological features are presented for 261 patients with identified β-thalassemia (β-thal) mutations. Mutations causing Hb S [β6(A3)Glu→Val]-β(0)-thal were IVS-II-849 (A>G) in 44%, frameshift codon (FSC) 6 (-A) in 14%, Hb Monroe [β30(B12)Arg→Thr] in 14%, and IVS-II-1 (G>A) in 10%. Mutations causing Hb S-β(+)-thal with 14-25% Hb A (type III) were -29 (A>G) mutation in 60%, -88 (C>T) in 22% and the polyadenylation signal site (polyA) (T>C) mutation in 14%, and in Hb S-β(+)-thal with 1-7% Hb A (type I), all had the IVS-I-5 (G>C) mutation. Hematologically, only minor differences occurred between the four Hb S-β(0)-thal mutations, but among the three mutations causing Hb S-β(+)-thal type III, levels of Hb A(2), Hb F, hemoglobin (Hb), MCV and MCH were highest in the -88 and lowest in the polyA mutations. Clinically, Hb S-β(0)-thal and Hb S-β(+)-thal type I were generally severe, and Hb S-β(+)-thal type III disease with the -88 mutation was milder than that caused by the polyA mutation.

Correlation of beta-thalassemia mutations with alpha-thalassemia: an experience of the southwestern region of Iran

BACKGROUND AND AIMS

Thalassemias are the commonest monogenic diseases worldwide. Mutations in genes coding for the globin proteins that alter protein output, produce the thalassemia syndromes. This study aimed to present the cases of alpha-thalassemia in beta-thalassemic patients from Khuzestan province in Iran.

MATERIALS AND METHODS

A total of 227 subjects (10-45 years, mean age of 14·8 years) including thalassemia patients (n=43), and their parents and siblings (n=184) from unrelated Khuzestani families were included in this study. The standard diagnostic marker for beta-thalassemia is elevation of the hemoglobin A2 (HbA2) level (>3·5%), while low mean corpuscular volume (MCV<80) and mean cell hemoglobin (MCH<27) with a normal HbA2 level indicate alpha-thalassemia carrier.

RESULTS

The amplification refractory mutation system polymerase chain reaction confirmed that among 227 subjects, 147 (64·75%) were heterozygous beta-thalassemia patients and 80 (35·25%) were identified either normal or with unknown mutations. Out of these 147 patients, nine cases were diagnosed as compound heterozygous. The IVS11-1(G-C) mutation was found in majority of chromosomes (40·08%). Out of nine beta/alpha-thalassemia patients, four showed -α(3·7)/αα (1·76%), two had -α(3·7)/-α(3·7) (0·88%), one had -α(4·2)/αα (0·44%) and one had - -MED/αα (0·44%) genotypes.

CONCLUSION

The present study suggests the need to establish a program for genetic counseling and prenatal diagnosis of beta-thalassemia for affected families and for initiating a control program by prospective screening of pregnant women. The application of the knowledge about mutation pattern was found to be beneficial since the mutations could be screened in the order in which they are present in our population. Hence, it will not only help to reduce the screening cost but also to promote early genetic counseling and prevention of an affected child.

Identification of a new mutation on the beta-globin gene: codons 8/9 (+AGAA); GAG.AAG.TCT(Glu-Lys-Ser)>GAG. AAAGAAG, in a patient from the north of France with a phenotype of beta-thalassemia minor

A 37-year-old man presented a slight debility. The hemogram showed a phenotype of beta-thalassemia minor: Hb (13.1 g/dL), mean corpuscular volume (MCV) (62 fL) with low mean corpuscular hemoglobin (MCH) (20.8 pg), associated with a high level of Hb A(2) of 5.3%. The serum ferritin level was 1,072 ng/mL. The sequencing of the mutated fragment revealed a duplication of four bases of codons 7/8 involving a shift in the open reading frame starting from codon 9 with a TGA stop codon at codon 23: codons 7/8/9 (+AGAA); GAG.AAG.TCT(Gly-Lys-Ser)>GAG.AAAGAAG. The human hemoglobin (Hb) instability tests were negative. The patient did not present the high iron Fe (HFE) mutation (C282Y, H63D). The same mutation was found in five other unrelated families (representing a total of 23 patients). All of their ancestors came from the north of France. This mutation has not been described before and could have its origins in the native populations of Northern France.

Hemoglobinopathies: a longitudinal study over four decades

BACKGROUND

Hemoglobinopathies are among the most common hereditary diseases worldwide, with high prevalence in the Mediterranean basin, Africa, and Asia. Although they are rare in the indigenous central European population, they have become much more common in Germany recently through the immigration of millions of people from endemic regions.

METHODS

In a long-term study (1971-2007), 100,621 hemoglobin analyses were performed and retrospectively evaluated. Basic clinical and hematological information were provided by the participating physicians. The hemoglobin defects were characterized with hematological and biochemical methods, as well as by DNA analysis in selected cases (from the mid-1980's onward). 73% of the analyses were performed in patients with an immigration background, 27% in patients of German ethnic origin.

RESULTS

34,228 persons, or 34% of those studied, were found to have a hemoglobinopathy. Most cases involved thalassemia syndromes (25,798 cases, 25.6%); the second most common type was a structural abnormality of hemoglobin (8,430 cases, 8.4%). This study provides the first broad overview of the occurrence, spectrum, and geographical distribution of hemoglobinopathies in Germany.

CONCLUSIONS

These data show that hemoglobinopathies are a relevant health problem in the population of Germany today. This is not an epidemiological study, and thus it is unknown to what extent these data are representative. Because hemoglobin defects are of widely diverse genetic and clinical types, specialized laboratory analysis is needed to diagnose them correctly and provide a basis for proper therapeutic decisions.

Epidemiology of haemoglobin disorders in Europe: an overview

OBJECTIVE

As a result of global population movements, haemoglobin disorders (thalassaemias and sickle cell disorders) are increasingly common in the formerly non-indigenous countries of Northern and Western Europe and in the indigenous countries of Southern Europe. This article presents an overview of the changing picture and a method for assessing service needs.

METHOD

Data on country of birth or ethnic origin of residents are adjusted to obtain the estimated proportions of residents and births in non-indigenous groups at risk for haemoglobin disorders in European countries. The results are combined with prevalence data in each country of origin to obtain country prevalence estimates. Service indicators (annual tests or other interventions required to ensure equitable delivery of treatment and prevention) are then derived by country.

RESULTS

Haemoglobin disorders now occur at comparable frequency throughout Northern, Western and Southern Europe. Annually, there are more affected conceptions in Northern and Western than in Southern Europe, and sickle cell disorders are more common than thalassaemias. There is growing need for health policy-makers to support motivated professionals working to develop optimal patient care, carrier diagnosis, genetic counselling and access to prenatal diagnosis throughout the Region.

CONCLUSION

There is a strong case for pan-European collaboration on haemoglobin disorders to share policies, standards and the instruments required to support them. These include methods for needs assessment, service standards, education and information strategies and materials, and methods for evaluating service delivery.

A cephalometric study on craniofacial morphology of Iranian children with beta-thalassemia major

OBJECTIVE

To study cephalometric and facial features of Iranian children with beta-thalassemia major.

DESIGN

Lateral cephalometric radiographs of thalassemic patients and controls who were matched for age, sex and ethnic origin were analyzed and compared.

SETTING AND SAMPLE POPULATION

A total of 30 thalassemic patients (18 male and 12 females) from Aliasghar Hospital, and 30 controls from the Orthodontic Department of Azad University.

OUTCOME MEASURE

Size and shape differences in the craniofacial complex between thalassemic patients and controls.

RESULTS

All thalassemic patients had a Class II skeletal base relationship with an average ANB angle of 8.75 degrees. There was no record of dramatic maxillary prognathism. However, the mandible of the thalassemic patients appeared to be smaller in size and more retruded in the face. A pronounced vertical growth direction was evident from angular and linear measurements. The dental deviations in thalassemic patients were mainly seen in the proclination and significant overeruption of incisors and increased overjet. Marked convex lower face and prominent upper and lower lips were evident from soft-tissue measurements.

CONCLUSION

Anemia does not only produce overgrowth of the maxilla. It also produces a retardation of condylar and ramal growth of the mandible producing Class II skeletal pattern.

An unexpectedly high frequency of heterozygosity for alpha-thalassemia in Ashkenazi Jews

alpha-Thalassemia is among the world's most common single gene disorders, which is most prevalent in the malaria belt. This geographic distribution has been attributed to a selective advantage of heterozygotes against this disease. Unexpectedly, we have found a high frequency of heterozygosity for deletional alpha-thalassemia (-alpha3.7) in Ashkenazi Jews (carrier frequency of 7.9%, allele frequency of 0.04). This population has resided in temperate climates for many centuries and was therefore not subjected to malarial selection pressure. In comparison, heterozygosity for beta-thalassemia, which is highly subject to malarial selection pressure, is very low (estimated <0.1%) in this group. It is possible that founder effect and genetic drift have contributed to the high frequency of deletional alpha-thalassemia in Ashkenazim, as may occur in closed populations. Alternatively, we hypothesize that positive selection pressure for an as yet unknown linked allele on chromosome 16 may be a significant factor leading to this high frequency.

Oral isobutyramide reduces transfusion requirements in some patients with homozygous β-thalassemia

The butyrate derivative isobutyramide (IBT) increases fetal hemoglobin (HbF) in patients with β-hemoglobinopathies, but little is known about its usefulness for prolonged therapeutic use. We treated 8 patients with transfusion-dependent β-thalassemia with 350 mg/kg of body weight per day of oral IBT for 126 to 384 days. During the trial period, the hemoglobin level was maintained between 85 g/L (range 82-87 g/L) (pretransfusion) and 115 g/L (range 110-119 g/L) (post-transfusion) (median, interquartile range), corresponding to 4-week transfusion intervals in all patients during the pretreatment phase. Adverse effects (bitter taste, epigastric discomfort) did not cause discontinuation of IBT. HbF increased in all patients from 3.1% (range 1.9%-4.8%) to 6.0% (range 3.3%-8.7) (P = .0017), while free Hb dropped from 0.48 g/L (range 0.39-0.81 g/L) to 0.19 g/L (range 0.16-0.24 g/L) (P < .0001). Transfusion intervals were consistently extended to 8 or 9 weeks in 1 patient, resulting in a decrease of daily iron load from 455 μg/kg per day (range 451-459 μg/kg per day) before therapy to 211μg/kg per day (range 203-286 μg/kg per day) during the 12-month treatment period. Prolongation of transfusion intervals achieved by IBT was less consistent in another patient, whose parenteral iron load nevertheless decreased from 683 μg/kg per day (range 618-748 μg/kg per day) to 542 μg/kg per day (340-596 μg/kg per day). In the other 6 patients, no prolongation of transfusion intervals was achieved. Response to treatment was associated with high pretreatment HbF (> 4.5%), high parental HbF, and increased erythropoietin levels (> 150 IU/L). We conclude that IBT prolongs transfusion intervals and reduces parenteral iron burden in some patients with transfusion-dependent β-thalassemia.

Oral isobutyramide reduces transfusion requirements in some patients with homozygous β-thalassemia

The butyrate derivative isobutyramide (IBT) increases fetal hemoglobin (HbF) in patients with β-hemoglobinopathies, but little is known about its usefulness for prolonged therapeutic use. We treated 8 patients with transfusion-dependent β-thalassemia with 350 mg/kg of body weight per day of oral IBT for 126 to 384 days. During the trial period, the hemoglobin level was maintained between 85 g/L (range 82-87 g/L) (pretransfusion) and 115 g/L (range 110-119 g/L) (post-transfusion) (median, interquartile range), corresponding to 4-week transfusion intervals in all patients during the pretreatment phase. Adverse effects (bitter taste, epigastric discomfort) did not cause discontinuation of IBT. HbF increased in all patients from 3.1% (range 1.9%-4.8%) to 6.0% (range 3.3%-8.7) (P = .0017), while free Hb dropped from 0.48 g/L (range 0.39-0.81 g/L) to 0.19 g/L (range 0.16-0.24 g/L) (P &lt; .0001). Transfusion intervals were consistently extended to 8 or 9 weeks in 1 patient, resulting in a decrease of daily iron load from 455 μg/kg per day (range 451-459 μg/kg per day) before therapy to 211μg/kg per day (range 203-286 μg/kg per day) during the 12-month treatment period. Prolongation of transfusion intervals achieved by IBT was less consistent in another patient, whose parenteral iron load nevertheless decreased from 683 μg/kg per day (range 618-748 μg/kg per day) to 542 μg/kg per day (340-596 μg/kg per day). In the other 6 patients, no prolongation of transfusion intervals was achieved. Response to treatment was associated with high pretreatment HbF (&gt; 4.5%), high parental HbF, and increased erythropoietin levels (&gt; 150 IU/L). We conclude that IBT prolongs transfusion intervals and reduces parenteral iron burden in some patients with transfusion-dependent β-thalassemia.

Beta-thalassemia intermedia associated with homozygosity for the -87 (C-->T) mutation in a Turkish family

We report on two siblings with beta+-thalassemia intermedia. Molecular studies of the beta-globin gene indicated that the patients are homozygous for the -87 (C-->T) mutation. This genotype has not been previously described. Homozygosity for the -87 (C-->T) mutation produces a mild form of beta+-thalassemia associated with moderate Hb F elevation (26-38%) and highly elevated Hb A2 (10-8.6%) levels, respectively. Hematological parameters of homozygous -87 (C-->G) and -87 (C-->A) mutations, and compound heterozygous patients with either C-->T, C-->G, or C-->A at -87 and one of the severe beta+- or beta0-thalassemia mutations, are given for comparison.

Dominant beta-thalassaemia: a highly unstable haemoglobin is caused by a novel 6 bp deletion of the beta-globin gene

Beta-thalassaemia is inherited as an autosomal recessive trait in most families. Particular interest has recently been focused on the molecular pathology of the rare forms with a dominant mode of inheritance. The index patient and her mother, who are described in this report, displayed typical clinical and haematological features of beta-thalassaemia intermedia with significant ineffective erythropoiesis and additional peripheral haemolysis. Molecular analysis demonstrated a heterozygous genotype for a novel 6 bp (TGGTCT) deletion of the beta-globin gene involving codons 33-35. This deletion results in the removal of two valine residues from the beta-globin chain at position 33/34 (B15/B16) and the substitution of the tyrosine residue at position 35 (C1) by an aspartic acid (beta 33-35 [B15-C1] Val-Val-Tyr-->0-0-Asp). According to the index patient's place of birth, this abnormal haemoglobin has been termed Hb Dresden. The stability of the variant and the normal beta-globin chains were similar during the incubation period of in vitro globin chain synthesis analysis. However, Hb Dresden is exquisitely unstable and cannot be detected in the peripheral blood by haemoglobin electrophoresis, high-performance liquid chromatography (HPLC) or isoelectric focusing. This instability can be explained by the vital structural role of the three affected amino acids that, in normal haemoglobin, establish a total of nine intermolecular bonds (five hydrophobic and four polar) at both the alpha1beta1 (alpha2beta2) and the alpha1beta2 (alpha2beta1) interface.

Binary specification of nonsense codons by splicing and cytoplasmic translation

Premature translation termination codons resulting from nonsense or frameshift mutations are common causes of genetic disorders. Complications arising from the synthesis of C-terminally truncated polypeptides can be avoided by 'nonsense-mediated decay' of the mutant mRNAs. Premature termination codons in the beta-globin mRNA cause the common recessive form of beta-thalassemia when the affected mRNA is degraded, but the more severe dominant form when the mRNA escapes nonsense-mediated decay. We demonstrate that cells distinguish a premature termination codon within the beta-globin mRNA from the physiological translation termination codon by a two-step specification mechanism. According to the binary specification model proposed here, the positions of splice junctions are first tagged during splicing in the nucleus, defining a stop codon operationally as a premature termination codon by the presence of a 3' splicing tag. In the second step, cytoplasmic translation is required to validate the 3' splicing tag for decay of the mRNA. This model explains nonsense-mediated decay on the basis of conventional molecular mechanisms and allows us to propose a common principle for nonsense-mediated decay from yeast to man.

Beta-thalassaemia

A complete spectrum of genetic lesions affecting the beta-globin gene giving rise to a complete spectrum of phenotypic severity is described. Although most of the molecular lesions involve the structural beta gene directly, some down regulate the gene through in-cis effects at a distance while trans-acting factors are implicated in a few cases. The remarkable phenotypic diversity can be related ultimately to the degree of alpha-globin-beta-globin chain imbalance and arises from variability of mutations affecting the beta gene itself and from interactions with other genetic loci, such as the alpha- and gamma-globin genes. The presence of other interacting loci is implicated by their interactions in increasing gamma gene expression or by an increased proteolytic capacity of the erythroid precursors. It is hoped that observations from the genotype-phenotype relationship might form the basis for a comprehensive diagnostic database that will be useful not only for genetic counselling and prenatal diagnosis but also for providing prognostic information for decision making in bone marrow transplantation and gene therapy programmes in the future. However, it is clear from recent analyses that, apart from the two categories of triplicated alpha genes with heterozygous beta-thalassaemia and inheritance of mild beta(+)-thalassaemia alleles, it is still not possible to predict consistently phenotype from alpha and beta genotypes alone owing to the influence of the other modulating factors, some implicated (such as inheritance of hereditary persistence of fetal haemoglobin) and others as yet unidentified.