The entire beta-globin gene cluster is deleted in a form of gamma delta beta-thalassemia

We have used restriction endonuclease mapping to study a deletion involving the beta-globin gene cluster in a Mexican-American family with gamma delta beta-thalassemia. Analysis of DNA polymorphisms demonstrated deletion of the beta-globin gene from the affected chromosome. Using a DNA fragment that maps greater than 40 kilobases (kb) 5' to the epsilon-gene as a probe, reduced amounts of normal fragments were found in the DNA of affected family members. Similar analysis using radiolabeled DNA fragments located 3' to the beta-globin cluster has shown that the deletion extends more than 17 kb 3' to the beta-gene, but terminates before the 3' endpoint of the Ghanian HPFH deletion. Hence, this gamma delta beta-thalassemia deletion eliminates over 105 kb of DNA and is the first report of a deletion of the entire beta-globin gene cluster.     

Gamma delta beta-thalassemia due to a de novo mutation deleting the 5'' beta-globin gene activation-region hypersensitive sites.

gamma delta beta-Thalassemia is a rare disorder of hemoglobin biosynthesis, characterized molecularly by partial or complete deletions of the beta-globin gene complex of 100 kilobases (kb) or greater. Common to all mutants described has been the deletion of the most-5' sequences of the beta-globin complex. We have used the techniques of pulsed-field gel electrophoresis and polymerase chain reaction to study a patient with a clinical gamma delta beta-thalassemia phenotype. This subject developed a de novo deletion on a maternally inherited beta-globin gene chromosome involving approximately 30 kb of sequences 5' to the epsilon gene; the deletion extends from -9.5 kb to -39 kb 5' of epsilon and includes three of the four DNase I hypersensitive sites (at -10.9 kb, -14.7 kb, and -18 kb 5' of epsilon). The remaining sequences of the beta-globin complex, including the DNase I hypersensitive sites at -6.1 kb and all structural genes in cis to the deletion are physically intact, but presumably nonfunctional, as evidenced by the presence of a beta S-globin gene that is not expressed as a sickle hemoglobin. Deletion of DNase I hypersensitive sites on a previously functional beta-globin gene complex confirms the significance of these sites in regulating globin gene expression.     

The same beta-globin gene mutation is present on nine different beta-thalassemia chromosomes in a Sardinian population.

The predominant beta-thalassemia in Sardinia is the beta 0 type in which no beta-globin chains are synthesized in the homozygous state. We determined the beta-thalassemia mutations in this population by the oligonucleotide-probe method and defined the chromosome haplotypes on which the mutation resides. The same beta 39(CAG----TAG) nonsense mutation was found on nine different chromosome haplotypes. Although this mutation may have arisen more than once, the multiple haplotypes could also be generated by crossing over and gene conversion events. These findings underscore the frequency of mutational events in the beta-globin gene region.     

beta-globin gene cluster haplotypes associated with beta-thalassemia on Corsica island

In the Corsican population, the incidence of beta-thalassemia traits is reported to be 3.1%. We have investigated the 2 more important beta-thalassemia mutations present in the Corsican population: beta0-39 and beta+IVS1-110. Seven polymorphic sites in the beta-globin gene cluster were analyzed from a sample of 43 non-related beta-thalassemia heterozygotes and of 47 nonrelated healthy individuals, from Central Corsica (Corte). Among the 43 Corsican patients analyzed, the nonsense codon is predominant (88.40%), whereas the beta+IVS1-110 mutation, the most common of beta-thalassemia in the eastern part of the Mediterranean basin, is underrepresented (2.33%). The other individuals did not show positive for the two tested mutations (9.27%). The beta0-39 mutation in the studied population shows a strong association with haplotype II (18.7%) and a weaker association with haplotypes I (2.3%) and VII (2.1%). The strong association of the beta0-39 mutation with haplotype II was also found in Sardinia, suggesting that the mutation on the two islands have the same origin. In the present study all the data concerning frequencies of the mutations and of sequence haplotypes, support the hypothesis of a western Mediterranean origin of the beta0-39 mutation. For the first time, this paper analyzes the association of beta-globin gene cluster haplotypes with the 2 more frequent beta-thalassemia mutations in an isolated population in the centre of Corsica (Corte), which presents certain genetic peculiarities. However, the analysis of beta-haplotypes will be very useful for the genetic epidemiological study in this region.     

Identification of a novel frameshift mutation at codon 53 (-T) in the beta-globin gene causing dominantly inherited beta-thalassemia in a Chinese Miao family

β-thalassemia, one of the most common inherited disorders of hemoglobin synthesis in the world, is genetically heterogeneous with over 200 different β-globin mutations worldwide. In this study, we describe a novel frameshift β-thalassemia mutation at codon (cd) 53 (−T) in exon 2 of the β-globin gene in a Chinese Miao family. In this family, all seven heterozygotes with this mutation presented with moderate anemia, jaundice, splenomegaly and elevated hemoglobin A2 levels. None of them had been transfused or carried any other known α/β-globin mutation. Pedigree analysis indicated an autosomal dominant inheritance pattern in this family. Two new haplotypes “−−−−+−+” and “−−+++−+” were identified by restriction fragment length polymorphism (RFLP) haplotype analysis. The former was associated with the cd53 (−T) mutation and the latter only existed in one family member. Thus, a novel frameshift cd53 (−T) mutation may lead to mild thalassemia intermedia even though there is no statistically significant difference in β-globin messenger RNA (mRNA) level between six heterozygotes and six normal subjects.     

A new mutation in the beta-globin gene (IVS II-850 G-C) found in a Yugoslavian beta-thalassemia heterozygote.

BACKGROUND. The recent development of laboratory techniques that can rapidly characterize the molecular defects of beta-thalassemia has resulted in the discovery of more than 100 different point mutations in the beta-globin gene. These mutations are population specific. About 20 of them account for over 90% of beta-thal genes in the world. The other mutations are usually found in single families. In this paper we describe a case with a novel mutation at position IVS II-850 (G-C) as a cause of beta-thalassemia. METHODS. Direct sequencing of PCR amplified DNA was used for the detection of the mutation. ASO probes were synthesized for dot-blot hybridization. Expression of the mutated allele was evaluated through Northern blot and RNA-PCR analyses. RESULTS. This mutation was found in four members of a family, who exhibited severe microcytosis and hypochromic anemia, with an average alpha/beta ratio of 2.0. The sequencing of PCR amplified DNA showed a G-C mutation at position IVS II-850 of the beta-globin gene. Dot blot analyses confirmed the presence of this substitution in all four carriers. Northern blot and RNA-PCR analyses did not reveal any abnormally spliced mRNA species. DISCUSSION. The G-C substitution at position IVS II-850 is the third mutation in the invariant AG dinucleotide of the acceptor splice site of the second intron of the beta-globin gene. It abolishes normal splicing, which leads to abnormally processed mRNA. It is a relatively rare mutation since it was not detected among the uncharacterized beta-thal chromosomes from Yugoslavia.     

The G----A mutation at position +22 3' to the Cap site of the beta-globin gene as a possible cause for a beta-thalassemia.

We describe the occurrence of a chromosome with a G----A mutation at position +22 relative to the Cap site that was found in five patients with beta-thalassemia. All patients had a common type of beta-thalassemia mutation on the second chromosome, namely the frameshift at codon 8 (-AA), the IVS-I-110 (G----A) and the IVS-II-1 (G----A) mutations. The beta genes of two patients, including the 5' and 3' untranslated regions, were completely sequenced and no other mutations, except a few polymorphic sites, were observed. Dot-blot analyses failed to demonstrate this G----A mutation at +22 in nearly 400 beta-thalassemia chromosomes and 180 normal chromosomes. Heterozygotes have the features of a high Hb A2-beta-thalassemia heterozygosity, although the hematological parameters might be less abnormal than observed in heterozygotes for the more common beta-thalassemia mutations. The possibility has been presented suggesting that this mutation might impair the binding of mRNA to ribosomes. Another mutation in this segment of DNA, i.e. a C----G mutation at position +20, is observed exclusively on a chromosome which also carries the C----G mutation at IVS-II-745. It is postulated that the +20 C----G mutation accentuates the beta-thalassemia condition caused by the IVS-II-745 mutation; the mechanism might be similar to that suggested for the G----A at +22 mutation.     

A novel basis for delta beta-thalassemia in a Chinese family

We have studied a Chinese family in which beta-thalassemia and delta beta-thalassemia were found in simple and compound heterozygous states. The delta beta-thalassemia heterozygote (the mother) had 22.3% hemoglobin F, of which 40% was G gamma and 60% A gamma; globin chain studies showed an alpha/beta + gamma ratio of 1.36. The compound heterozygote for delta beta-thalassemia and beta-thalassemia (the child) had the clinical picture of thalassemia intermedia and an alpha/beta + gamma ratio of 4.44. Gene mapping studies were performed using DNA from the affected child. Seventy kilobases of DNA in the beta- globin gene cluster starting upstream from the epsilon-globin gene and ending downstream from the beta-globin gene were mapped, and no detectable deletions or rearrangements were detected. In addition, heterozygosity was detected at multiple polymorphic restriction sites in and 3' to the beta-globin gene, which excludes the possibility of a deletion of the entire beta-globin gene cluster. This is the first example of a nondeletion delta beta-thalassemia associated with increased expression of both G gamma and A gamma genes.     

A new insertion mutation in the beta-globin gene [codons 45/46 (+A)] resulting in a beta-thalassemia minor phenotype

The beta-globin gene of 306 newly diagnosed beta-thalassemia (thal) minor patients were sequenced. Analysis revealed that only one amongst all the identified mutations had not been previously reported. This new mutation, causing a beta(+)-thal minor phenotype, was found in a patient of Arabic origin. The insertion frameshift mutation (+A) between codons 45 and 46 [codons 45/46 (+A)] results in a premature termination signal at codon 52. No truncated beta-globin or abnormal hemoglobin (Hb) was identified.     

Molecular characterization of a beta-globin gene deletion of 1357 bp in a Taiwanese beta-thalassemia carrier

A 30-year-old male had hypochromic microcytosis and elevated Hb F and Hb A(2) levels (MCV 72.5 fL, MCH 25.2 pg, Hb F 8.9% and Hb A(2) 6.6%). Direct DNA sequencing of the entire beta-globin gene revealed no anomalies. Multiplex ligation-dependent probe amplification (MLPA) showed reduced signals at probes for the promoter, 5'UTR (5' untranslated region), exon 2 and intron 2 regions of the beta-globin gene. Gap-polymerase chain reaction (gap-PCR) successfully obtained junctional fragments. Direct sequencing of the gap-PCR product revealed that the 5' breakpoint was located at -548 (relative to the Cap site of the beta-globin gene) and the 3' breakpoint was located at +810 in the second intron of the beta-globin gene. A total of 1357 bp were deleted (NG_000007.3:g.69997_71353del1357). Similar to another two beta-globin gene deletions reported in Black and Croatian thalassemia carriers, respectively, this deletion was the result of a non homologous breakage and reunion event.     

Successful treatment of murine beta-thalassemia intermedia by transfer of the human beta-globin gene

The beta-thalassemias are caused by more than 200 mutations that reduce or abolish beta-globin production. The severity of the resulting anemia can lead to lifelong transfusion dependency. A genetic treatment based on globin gene transfer would require that transgene expression be erythroid specific, elevated, and sustained over time. We report here that long-term synthesis of chimeric hemoglobin (mualpha(2):hubeta(A)(2)) could be achieved in mice with beta-thalassemia intermedia following engraftment with bone marrow cells transduced with a lentiviral vector encoding the human beta-globin gene. In the absence of any posttransduction selection, the treated chimeras exhibit durably increased hemoglobin levels without diminution over 40 weeks. Ineffective erythropoiesis and extramedullary hematopoiesis (EMH) regress, as reflected by normalization of spleen size, architecture, hematopoietic colony formation, and disappearance of liver EMH. These findings establish that a sustained increase of 3 to 4 g/dL hemoglobin is sufficient to correct ineffective erythropoiesis. Hepatic iron accumulation is markedly decreased in 1-year-old chimeras, indicating persistent protection from secondary organ damage. These results demonstrate for the first time that viral-mediated globin gene transfer in hematopoietic stem cells effectively treats a severe hemoglobin disorder.     

Human chromosome 7 carries the beta 2 interferon gene.

A cDNA clone (pAE20-4) corresponding to the 1.3-kilobase human beta 2 interferon mRNA was used as a probe in blot-hybridization experiments of DNA from a panel of human-rodent somatic cell hybrids containing overlapping subsets of human chromosomes. The DNA hybridization experiments showed that the human beta 2 interferon gene is located on human chromosome 7. This assignment is consistent with previous experimental data in which the expression of the translationally active 1.3-kilobase beta 2 interferon mRNA was assayed in various somatic cell hybrids. Blot-hybridization experiments using DNA from different human cell strains and cell lines reveal distinct EcoRI restriction fragment length polymorphisms of the human beta 2 interferon gene.     

Increased protein binding to a -530 mutation of the human beta-globin gene associated with decreased beta-globin synthesis

Although some cases of the syndrome of hereditary persistence of fetal hemoglobin (HPFH) have been correlated with mutations causing a change in the binding of trans-acting factors to DNA sequences flanking the gamma-globin gene, this mechanism has not been described in beta-thalassemias upstream of the canonical promoter of the beta-globin gene. In this report we describe such a change in binding of a protein that may explain a silent carrier phenotype of beta-thalassemia. We have previously demonstrated the binding of a protein (BP1) derived from a nuclear extract of human K562 cells to DNA 5' to the human beta-globin gene in a region having a negative regulatory function. The binding of BP1 in this region can be detected by DNAse I footprinting and by gel mobility shift analysis. We have now compared binding of BP1 to the normal sequence and a mutated sequence (+ATA/-T at -530 bp from the cap site) from the silent carrier of beta-thalassemia. Using mobility shift assays we show that BP1 binds about nine times more strongly to the mutated sequence than the normal sequence. These results suggest the possibility that the decreased expression of the beta-globin gene exhibited by the carrier may be due, at least in part, to tighter binding of a protein which functions as a negative control element or repressor.     

A novel Indian beta-thalassemia mutation in the CACCC box of the promoter region

This is the first report of a previously undescribed mutation in Indian subjects of the CACCC box of promoter region for beta-globin, which in combination with a common mutation produces thalassemia major in the offspring of the family.     

Human globin gene analysis for a patient with beta-o/delta beta-thalassemia.

Complementary DNA (cDNA) was prepared with RNA-dependent DNA polymerase from human globin messenger RNA (mRNA). Annealing and translation experimenta with total mRNA from circulating cells from a patient with heterozygous beta/heterozygous beta-delta-o thalassemia (beta-o/delta beta-o-thalassemia) demonstrated no detectable mRNA for beta-globin. cDNA enriched in sequences homologous to beta-globin mRNA was prepared by hydroxylapatite fractionation of hybrids formed between beta-o/delta beta-o-thalassemic mRNA and cDNA made from mRNA from a patient with alpha-thalassemia (hemoglobin H disease). The rate of annealing of this beta-enriched cDNA to normal human nuclear DNA was that of a sequence present as only a single copy per haploid genome. The beta-enriched cDNA annealed to the beta-o-delta beta-o-thalassemia total DNA with approximately the same kinetics as to normal DNA, indicating that no total gene deletion of beta-globin genes from the diploid genome has occurred, although the accuracy of the technique could not exclude with certainty a partial deletion or a deletion of a beta-globin gene from only one of the haploid genomes. This demonstrates that at least one of the beta-o- or the delta beta-o-thalassemia haploid genomes in this case contains a substantially intact beta-globin gene.     

Normal delta-globin gene sequences in Sardinian nondeletional delta beta-thalassemia.

In order to clarify the reasons for the reduced Hb A2 levels in Sardinian delta beta-thalassemia, we characterized, both by cloning and sequence analysis and by direct sequencing of amplified DNA, the delta-globin gene from an individual of Sardinian descent who is a compound heterozygote for the beta zero-thalassemia codon 39 (C-->T) nonsense mutation and the Sardinian delta beta-thalassemia [codon 39(C-->T)/-196(C-->T)A gamma]. The analysis of the delta-globin gene from the delta beta-thalassemia chromosome revealed an entirely normal sequence. The defective function of the delta-globin gene in this determinant is thus likely related to a suppressive effect of the in cis nondeletional high persistence of fetal hemoglobin mutation of the A gamma gene, probably resulting from an increased capability of the relative promoter to interact with the locus control region.