Molecular characterization of a novel 10.3 kb deletion causing β-thalassaemia with unusually high Hb A2

A family of Asian-Indian descent has a variant form of beta-thalassaemia characterized by unusually high levels of Hb A2 in the heterozygous state. The propositus who is homozygous for the mutation has thalassaemia intermedia. Restriction endonuclease mapping suggested the presence of a 10.3 kilobase (kb) deletion removing the whole of the beta-globin gene. Subsequently, molecular analysis was performed by directly sequencing a specifically amplified region of genomic DNA. A 10329 basepair deletion was precisely defined which results in the loss of the 5' beta promoter region and the entire beta-globin gene. The deletion extends from 3011 bp 5' to the mRNA cap site to an L1 repeat element downstream of the beta-globin gene and is very similar to the 12.6 kb deletion of Dutch beta zero-thalassaemia. In common with four other mutations, both these deletions remove the 5' promoter region of the beta gene and all are associated with unusually elevated levels of Hb A2 in the heterozygous state.     

Australian β0-thalassaemia: a high haemoglobin A2β0-thalassaemia due to a 12 kb deletion commencing 5''to the β-globin gene

A large novel deletional beta zero-thalassaemia mutation associated with unusually high levels of haemoglobin A2 in heterozygotes is described in an Australian family. The deletion was characterized by restriction enzyme analysis followed by PCR amplification and sequencing of the breakpoint region. Australian beta zero-thalassaemia extends from 835 basepairs (bp) 5' to the cap site of the beta-globin gene downstream for 12.023 kb. This deletion, similar to previously described deletional beta zero-thalassaemias associated with high Hb A2, removes sequences 5' to the beta-globin gene promoter and emphasizes the functional importance of the 5' beta-globin region in eliciting the unusually high Hb A2 phenotype.     

High Hb A2 beta-thalassemia due to a 468 bp deletion in a patient with Hb S/beta-thalassemia

We describe a case of Hb S/beta-thalassemia (thal) involving a 468 bp deletion that removes the beta-globin gene promoter but leaves the coding regions intact. This is the second report of this deletion, and our family study establishes that this deletion causes beta0-thal with unusually high levels of Hb A2 and Hb F. As with other genotypes involving deletions of the 5' region of the beta-globin gene, our patient had a mild form of Hb S/beta-thal.     

A β°-thalassaernia due to a 1605 bp deletion of the 5'β-globin gene region

Summary. We studied a heterozygous β°-thalassaemia patient from Croatia with an unusually high Hb A₂ level of 7.6% and an elevated Hb F level of 5.8%. The same condition was found in his father (Hb A₂ 8.2%; Hb F 8.5%). Gene mapping and direct sequencing analyses revealed a new deletion of 1605 bp in the 5'β-globin gene region between positions —984/5 and +620/1. This deletion has not been observed among more than 500 P-thalassaemia chromosomes from the Balkan countries studied in our laboratory.     

Hb S/beta zero-thalassemia due to the approximately 1.4-kb deletion is associated with a relatively mild phenotype.

We report a relatively mild phenotype associated with two siblings who are compound heterozygotes for Hb S and a beta zero-thalassemia mutation due to a approximately 1.4-kb deletion of the 5' region of the beta-globin gene. Each is found to have unusually high levels of Hb A2 and Hb F, accounting for more than 20% of the total hemoglobin. These may interfere with intracellular Hb S polymerization, thus leading to a mild clinical course.     

A novel 105 basepair deletion causing beta(0)-thalassemia in members of a Thai family.

We identified and characterized a novel beta(0)-thalassemia mutation due to partial deletion of the 5' end beta-globin gene including the mRNA cap site and a part of exon 1. The deletion was precisely 105 basepair (bp) in length extending from position -24 or -25 to +80 or +81 relative to the beta-globin gene mRNA cap site. This mutation was detected in three individuals from a family originating in the area of southern Thailand. The propositus was a 39-year-old female and noted to be heterozygous for beta-thalassemia with hemoglobin (Hb) level of 10.1 g/dl, MCV 70 fl, MCH 23.1 pg, HbA2 6.3%, and HbF 2.4%. Her son was 9 years of age and was also heterozygous for the mutation, having Hb level of 10.8 g/dl, MCV 58 fl, MCH 19.0 pg, HbA2 5.6%, and HbF 4.3%. Her 6-year-old daughter was affected, having a genotype of this mutation and a G-C transition at IVS 1 nt 5. Although the deletion does not include the beta-globin gene promoter sequences, the individuals heterozygous for this mutation have an elevated HbA2 level slightly higher than observed in most carriers of beta-thalassemia caused by point mutations.     

Characterization of Two Novel Deletions Involving the 5′ Region of the β-Globin Gene

We report two novel β-thalassemia (β-thal) deletions involving the 5′ region of the β-globin gene (HBB). The first deletion spans 538?bp and removes the β-globin promoter, 5′ untranslated region (5′UTR) and most of exon 1. This deletion was identified in a 3-year-old Vietnamese boy with non transfusion dependent Hb E (HBB: c.79G>A)/β⁰-thal. The second deletion spans 1517?bp and removes the β-globin gene promoter, 5′UTR, and exons 1 and 2. This deletion was identified in two unrelated adults of European descent who had β-thal trait with unusually high Hb A₂ levels. Deletions such as these are generally associated with higher levels of Hb A₂ and Hb F than typical β-thal alleles, which may ameliorate the severity of the disease.     

Characterization of a novel deletion causing (deltabeta)0-thalassemia in a Thai family

A novel deletion of the human beta-globin gene cluster associated with the increased level of fetal hemoglobin (Hb F) in adult life has been demonstrated in a Thai family. A Thai girl who was mistakenly diagnosed as beta-thalassemia/HbE is found to be the compound heterozygote of this mutation and Hb E. The heterozygous father had mild hypochromic and microcytic red blood cells and a high level of Hb F (23.2%). Polymorphic restriction sites in the beta-globin gene cluster identified the homozygous alleles, which localized the deletion region between the psibeta-globin and the 3' beta-globin genes. DNA polymerase that can amplify a long DNA template was employed to examine DNA fragment encompassing this deletion. A 11.3 kilobases (kb) of DNA deletion, beginning approximately 3.1 kb 5' to the delta-globin gene and end in the intron 2 of the beta-globin gene was detected. DNA analysis revealed that this is a case of (deltabeta)(0)-thalassemia with a novel mutation, which can lead to a mild form of beta-thalassemia upon interaction with Hb E.     

High Hb A2 β-Thalassemia Due to a 468 bp Deletion in a Patient with Hb S/β-Thalassemia

We describe a case of Hb S/β-thalassemia (thal) involving a 468 bp deletion that removes the β-globin gene promoter but leaves the coding regions intact. This is the second report of this deletion, and our family study establishes that this deletion causes β⁰-thal with unusually high levels of Hb A₂ and Hb F. As with other genotypes involving deletions of the 5′ region of the β-globin gene, our patient had a mild form of Hb S/β-thal.     

A monoclonal antibody (NMC-VIII/10) to factor VIII light chain recognizing Glu1675–Glu1684 inhibits factor VIII binding to endogenous von Willebrand factor in human umbilical vein endothelial cells

We have outlined a fast, non-radioactive strategy to identify point mutations in the 5' flanking region of the gamma-globin genes using denaturing gradient gel electrophoresis (DGGE) of amplified DNA. In a sample of previously characterized carriers of non deletion-type hereditary persistence of fetal haemoglobin (HPFH) the different point mutations in both gamma gene promoters could be easily identified by DGGE of a 327 bp fragment. A 4 bp deletion at position -225 to -222 of the A gamma globin gene was unexpectedly found in several samples and shown to represent a frequent polymorphism. Analysis of a 681 bp fragment specific for the 5' region of the A gamma gene, showed that this can be used to determine the haplotype of the chromosome under study. This technique may be useful in the study of sequence variations associated with high Hb F expression in physiological and pathological conditions.     

Homozygosity for a new type of G gamma (A gamma delta beta)zero-thalassemia in a Malaysian male

Hematological and clinical data are presented for a young Malay patient with a homozygous (delta beta)zero-thalassemic condition. His red blood cells contained 100% fetal hemoglobin with alpha and G gamma chains only. Detailed gene mapping defined a large deletion with a 5' end between the Aha III and Apa I sites, some 200-400 bp 5' to the A gamma globin gene and a 3' end beyond sequences 17-18 kb 3' to the beta globin gene. This G gamma (A gamma delta beta)zero-type of thalassemia is different from all the other six types described before. Comparison of the hematological data of this patient with those of homozygotes for either the Sicilian or Spanish types of G gamma A gamma (delta beta)zero-thalassemia showed no differences; all homozygotes have a moderate anemia which is accentuated by the relatively high oxygen affinity of the Hb F containing erythrocytes.     

A novel deletion of approximately 27 kb including the beta-globin gene and the locus control region 3'HS-1 regulatory sequence: beta zero- thalassemia or hereditary persistence of fetal hemoglobin?

A novel deletion of approximately 27 kb with the 5' breakpoint 1.5 to 2.2 kb upstream of the beta-globin gene, and the 3' breakpoint approximately 24 kb downstream of the beta-globin gene, has been found in five members of two families from Southeast Asia (Vietnam and Cambodia). Six members of another family from China, previously reported from our laboratory, have also been shown to carry this deletion. The patients presented with mild hypochromia and microcytosis, a hemoglobin (Hb) A2 level of approximately 4.0%, and a markedly increased, heterocellularly distributed, Hb F level (14.0 to 26.0%). In vitro globin-chain synthesis showed a mild imbalance with appreciable gamma-chain compensation (alpha/beta + gamma ratio of 1.46). The 3' end of this deletion includes the 3'HS-1, and we hypothesize that removal of this region results in the loss of its gamma-globin gene-silencing effect, which causes a markedly elevated Hb F level with a modest increase in Hb A2 levels, unlike the situation in other deletional beta zero-thalassemias. The possible influence of particular sequence variations in the locus control region 5'HS-2 and the G gamma promoter, present on the chromosome with this deletion, on the overall gamma-globin gene should also be considered.     

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.     

High hemoglobin A2 beta 0-thalassemia due to a 532-basepair deletion of the 5' beta-globin gene region

We identify and characterize a novel beta 0-thalassemia mutation that is associated with an unusually high level of hemoglobin (Hb) A2 in the heterozygote. This newly discovered mutation is caused by a 532-basepair deletion that extends from positions -454 to + 78 relative to the mRNA cap site of the beta-globin gene. The propositi are 9-month-old fraternal twins. One of the twins is a compound heterozygote for the deletion and Hb S, the other is a compound heterozygote for the deletion and Hb C.     

Molecular and hematologic characterization of Scottish-Irish type (epsilon gamma delta beta)zero thalassemia

The DNA deletion associated with an example of (epsilon gamma delta beta)zero thalassemia (Scottish-Irish type) was characterized. The deletion is approximately 205 kb in length and involves the epsilon, G gamma, A gamma, delta, and beta globin genes. The breakpoint is located 263 bp 3' to exon 3 of the beta globin gene. An LI (KpnI) repeat element approximately 320 bp in size is found at the 3' end of the novel DNA sequence. Different clinical phenotypes for three heterozygous neonates suggest that the deletion alone does not predict severity of (epsilon gamma delta beta)zero thalassemia at this age.     

The 12.6 kilobase DNA deletion in Dutch β°-thalassaemia

The Dutch beta zero-thalassaemia has few clinical symptoms in homozygotes, elevated fetal haemoglobin (4-11%) in heterozygotes, and has a DNA deletion previously estimated as 10 kb which removes the beta-globin gene (Gilman et al, 1984). A DNA fragment containing the breakpoints of the Dutch beta zero-thalassaemia deletion has now been cloned. Sequencing across the deletion junction region showed the 3' endpoint to be about 3 kb further 3' than originally thought, so that the deletion covers 12.6 kb. The 3' endpoint lies in a region of Kpn I (L1) repeated sequences, which is also the case for several other deletions. A six bp region of homology (AAATTT) between the 5' and 3' normal sequences at the breakpoint may have contributed to the non-homologous recombination event that led to the Dutch beta zero-thalassaemia deletion. The 12.6 kb Dutch beta zero-thalassaemia deletion is now seen to be a member of a 12-13 kb size category of deletions which also includes two delta beta-thalassaemias.