The β- and δ-Thalassemia Repository (Seventh Edition)

Molecular characterization of beta-thalassemia genes in an Argentine population

This study was designed to identify the beta-thalassemia mutations in an Argentine population. Seventy-one pediatric patients and 101 available relatives were studied (85 chromosomes). Diagnosis of beta-thalassemia was made by conventional hematological procedures. Molecular studies were carried out by dot-blot and restriction endonuclease analysis on amplified DNA to detect the eight most frequent mutations in the Mediterranean area. We were able to identify 95.3% of the beta-thalassemia mutations in the subjects under study. The four common defects (C-39, 47%; IVS-I nt 110, 22.4%; IVS-I nt 1, 9.4%; and IVS-I nt 6, 5.9%) account for 84.7% of the beta-thalassemia alleles. The alleles and their distributions showed a close similarity to the spectrum of alleles in Italy. The differences might represent the influence of other immigrations, especially from Spain. We conclude that beta-thalassemia in Argentina originated mainly from Italian immigrants. This study will enable us to design an adequate approach to genetic counseling and/or prenatal diagnosis for couples at risk.

Detection of eight beta-thalassemia mutations using a DNA enzyme immunoassay

We describe the use of a polymerase chain reaction-based method followed by a DNA enzyme immunoassay for the simultaneous detection of the eight most common beta-thalassemia mutations in the Mediterranean population. The method is specific, sensitive, and easily applicable in routine clinical laboratories for the molecular diagnosis of beta-thalassemia patients and at risk couples.

Hb Lulu Island (alpha 2 beta 2 107[G9]Gly-->Asp)-beta zero- thalassemia (codon 15; TGG-->TAG), a form of thalassemia intermedia

Hb Lulu Island [beta 107(G9)Gly-->Asp] was discovered in an East Indian female who carried a common beta zero-thalassemia allele, i.e., codon 15, TGG-->TAG (is a stop codon) in trans. Both abnormalities were detected through sequencing of the amplified beta-globin genes and were confirmed by hybridization with 32P-labeled probes. Hb Lulu Island is mildly unstable with a borderline decrease in oxygen affinity; its instability is less severe than that of Hb Burke or beta 107(G9)Gly-->Arg. The compound heterozygosity expresses as a thalassemia intermedia with moderate anemia, a variable need for blood transfusions, Heinz body formation, and a red cell morphology which is typical for such a condition. The level of HbA2 was greatly increased (6.5-7.0%) as was the delta chain level (12% of total non-alpha) probably because of the instability of Hb Lulu Island and the decreased ability of the beta x chain to form dimers with the normal alpha chain.

Advances in the prenatal and molecular diagnosis of the hemoglobinopathies and thalassemias

Prenatal diagnosis is available for pregnancies at risk for virtually all inherited disorders of hemoglobin production. The field of reproductive genetics must confront many ethical, legal, and social concerns regarding its use, many of which derive from a woman's desire to bear children but legal right to abortion. The goal of more widespread utilization of prenatal diagnosis is sought in the context of questioning the ethical control to be exerted over the biological makeup of future generations. Its appropriate application would be facilitated greatly by the availability of reliable DNA markers of disease severity. Advances in fetal sampling and in detecting mutant globin genes have provided the safe, accurate methodology required for prenatal diagnosis. Chorionic villus sampling in the first trimester has become standard practice, but second trimester amniocentesis also is used for sampling fetal DNA. The use of preimplantation diagnosis and testing fetal cells from the maternal circulation will soon be practical. DNA-based detection of globin gene mutations has been facilitated greatly by the polymerase chain reaction revolution, and several reliable diagnostic methods are available. Polymerase chain reaction-based methods rely on restriction analysis, allele-specific hybridization or amplification, DNA sequence analysis, and new non-polymerase chain reaction methods for DNA amplification in vitro. These methods are available for detecting hemoglobinopathy, thalassemia, and thalassemic-hemoglobinopathy genes that affect alpha- or beta-globin loci.

A novel amber mutation in a beta zero-thalassaemia gene (beta 37TGG-->TAG), with direct detection by mapping the restriction fragments in amplified genomic DNA

A novel amber mutation, a G to A substitution at the second position of codon 37 in the beta-globin gene that changes the tryptophan coding triplet (TGG) to a termination codon (TAG), was found in a Chinese beta-thalassaemia carrier. The mutant gene creates an additional Dde I recognition site and eliminates the Ava II site, so this point mutation can be directly identified by restriction enzyme analysis.

Reverse dot-blot detection of Thai beta-thalassaemia mutations

Pending curative therapy, newborn screening and prenatal diagnosis are essential to the management of beta thalassaemia. Diagnosis using electrophoretic methods is difficult in the presence of composite phenotypes and high Hb F levels. Direct DNA detection of mutant alleles circumvents both problems, but the enormous diversity of beta-thalassaemia mutations poses challenges for this approach. Among PCR-based tests, the reverse dot-blot method enables screening several mutations with a single hybridization reaction. Unfortunately it has often been targeted to only the common mutations of a particular ethnic population, necessitating the use of more arduous detection methods for the less common mutations. We developed a reverse dot-blot strip for the 10 beta-thalassaemia mutations, including the beta-thalassaemic haemoglobinopathies Hb E and Hb Malay, that account for 96% of beta thalassaemia in Thailand, and another strip for six less common Thai mutations. The second strip precludes the need for more technically challenging methods. To avoid problems associated with secondary structure of amplified full-length target DNA, we amplified and labelled beta-globin DNA as two shorter fragments that encompassed all known Thai mutations. Reverse dot-blotting is a rapid, accurate method for detecting beta-thalassaemia mutations.

Initiation codon mutation (ATG --> ATA) of the beta-globin gene causing beta-thalassemia in a Swedish family

An initiation codon mutation ATG-->ATA of the beta-globin gene was found in seven members of three generations of a family living in northern Sweden. This mutation, which has not previously been described, changes the initiation codon for methionine into a codon for isoleucine and will then result in a beta zero-thalassemic phenotype. The affected family members all present hematological findings typical for beta-thalassemic trait, with slight anemia, marked microcytosis, and increased levels of Hb A2.

Genetic heterogeneity of beta-thalassemia in southeast Sicily

In this study we have defined the spectrum of the beta-thalassemia mutations, the beta-thalassemia haplotypes, and the genotype-to-phenotype correlations in a large number of patients with different beta-thalassemia conditions. Seventeen different beta-thalassemia mutations were detected which included one chromosome each with Hb Dhonburi and Hb Lepore. Five alleles, namely, codon 39 (C-->T), IVS-I-110 (G-->A), IVS-I-6 (T-->C), IVS-II-745 (C-->G), and IVS-I-1 (G-->A), account for 90% of all beta-thalassemia mutations in 846 thalassemic chromosomes studied. Haplotyping for a large number of subjects showed that the five common mutations are linked to a few haplotypes. The presence of milder mutations, mainly IVS-I-6 (T C), in about 19% of our patients explains some of the clinical variables. Among the 37 patients with thalassemia of intermediate severity, only 6 were homozygous or compound heterozygous for two severe alleles. The type of beta-thalassemia is the main factor responsible for differences in the phenotypic expression of the disease in patients with Hb S-beta-thalassemia; patients with Hb S-beta(+)-thalassemia are less severely affected than those with Hb S-beta(0)-thalassemia. The five most frequent mutations have comparable distributions all over Sicily.

The frequency of 14 beta-thalassemia mutations in the Arab populations

The beta-thalassemias are a heterogeneous group with respect to molecular pathogenesis, and different populations and ethnic groups differ with respect to the predominating mutations. This variable spectrum of beta-thalassemia mutations has resulted in extensive studies in each population and ethnic group to identify the major mutations. In this study we investigated the prevalence of 14 mutations in 253 beta-thalassemia patients drawn from eight Arab countries (i.e. Jordan, Egypt, Syria, Lebanon, Yemen, and Saudi Arabia), living in Saudi Arabia and attending Ministry of Health hospitals. The mutations investigated included IVS-I-110 (G-->A), IVS-II-1 (G-->A), IVS-I-5 (G-->C), codon 39 (C-->T), IVS-I-1 (G-->A), frameshift at codons 8/9 (+G), frameshift at codons 41/42 (-TTCT), codon 15 (TGG-->TAG), IVS-I-6 (T-->C), frameshift at codon 16 (-C), IVS-II-745 (C-->G), codon 6(-A), IVS-I, 3' end (-25 bp), and Cap +1 (A-->C). The most frequently encountered mutations were IVS-I-110 and IVS-II-1 which were identified in the population of each Arab country. The IVS-I-1 and IVS-II-745 mutations were encountered in Jordanians, Egyptians, and Syrians. The IVS-I-5, codon 39, codon 6, IVS-I, 3' end (-25 bp), and Cap +1 mutations were encountered only in Saudis and not in other Arabs, except codon 39 which was present in the Syrians and Lebanese. Other mutations were generally rare and not specific to any Arab ethnic group. This paper presents preliminary data on the prevalence of 14 mutations in the Arab populations and shows wide variation in the molecular basis of beta-thalassemia in different Arab ethnic groups. Further detailed studies to identify the entire spectrum of beta-thalassemia mutations are stressed.

RNA transcripts of the beta-thalassaemia allele IVS-2-654 C-->T: a small amount of normally processed beta-globin mRNA is still produced from the mutant gene

IVS-2-654 C-->T is a common Chinese beta-thalassaemia mutation. Previous studies report that this mutation resulted in the formation of an abnormally spliced mRNA and the absence of detectable normal beta-globin mRNA, hence the mutation was considered to cause beta o-thalassaemia. We recently used the method of PCR amplified cDNA copies of circulating erythroid cell mRNA to analyse the mutant gene transcripts and found that this IVS-2-654 mutation does not abolish normal RNA processing entirely, but that a significant amount (over 15%) of normally processed beta-globin mRNA is produced. Microglobin chain biosynthetic analysis using the HPLC method showed that beta-globin chain was also present in the blood of patients with IVS-2-654 C-->T mutation. Accordingly, this mutant allele leads to a beta (+)-thalassaemia. Further, the methodology described in this paper provides a new approach towards the detection of RNA transcripts of beta-thalassaemia alleles as well as the study of gene expression in beta-thalassaemia and other genetic diseases.

Molecular characterization of beta-thalassemia in north Jordan

We have studied the beta-thalassemia mutations in 91 chromosomes of 43 patients with beta-thalassemia major and five with Hb S-beta-thalassemia, aged 6 months to 24 years. Many are blood transfusion-dependent and are being treated at the major hospital, the Princess Basma Hospital, in Irbid, Jordan. As many as 13 different mutations have been identified; three Mediterranean mutations [IVS-I-110 (G-->A), IVS-II-I (G-->A), and IVS-II-745 (C-->G)] were present in 54% of the chromosomes tested, while six other Mediterranean alleles were found in 24% of the chromosomes, for a total of 78% of Mediterranean origin. Sixteen chromosomes carried mutations which were observed in Arabian, Southeast Asian/Indian, and Iranian/Egyptian or Black populations; four beta-thalassemia mutations remained unidentified.

Detection of common deletional alpha-thalassemia-2 determinants by PCR

We have developed a rapid approach to detect the two most common alpha-thalassemia-2 (alpha-thal-2) determinants by the polymerase chain reaction (PCR) technique, which takes a few hours to complete. Specific oligonucleotides selectively amplify appropriate segments of the chromosome with the deletion and the normal chromosome under identical experimental conditions, and the products are identified by electrophoresis on 1.5% agarose. Characterization of the two most prevalent types of the -alpha 3.7 determinant [-alpha 3.7(I) and -alpha 3.7(II)] can be made by Apa I digestion of the PCR product. Two types of alpha-thal-2 determinants, -alpha 3.7 and -alpha 4.2, were tested in numerous samples from various parts of the world. This approach is believed to provide a cost-effective way to screen large numbers of blood samples in a relatively short time and can be used to identify alpha-thal-2 heterozygotes and homozygotes and compound heterozygotes (-alpha 3.7/-alpha 4.2) in populations where such alpha-gene defects are shown to exist at high frequencies.

Alpha and beta thalassaemia among Chinese children in Guangxi Province, P.R. China: molecular and haematological characterization

We have studied nearly 100 patients with beta-thalassaemia major and 60 patients with Hb H disease who were attending the Haematology Clinic of Guangxi Medical College. Treatment of the patients was limited and only a few patients with beta-thalassaemia major received blood transfusion(s). As a result, the severe anaemia has led to early death at 3-4 years for beta zero-thalassaemia homozygotes, and 8-12 years for beta(+)-thalassaemia homozygotes. Four beta-thalassaemia alleles are responsible for nearly 90% of all beta-thalassaemia chromosomes. This information has resulted in the initiation of a prenatal testing programme at the local level. The patients with Hb H disease maintained a haemoglobin level of 6-10 g/dl and early death was infrequently observed. The --SEA deletion was the major type of alpha-thalassemia-1, while three smaller deletions (-2.7, -3.7 and -4.2 kb) and two nondeletional alpha-thalassaemia determinants (Hbs Constant Spring and Quong Sze) were the alpha-thalassaemia-2 types.