The 18- to 23-kb deletion of the Macedonian delta beta-thalassemia includes the entire delta and beta globin genes

Restriction endonuclease mapping analyses were made of DNA from a few members of a Macedonian family with hematological characteristics of delta beta-thalassemia, ie, microcytosis, normal HbA2 levels, and elevated levels of HbF (7% to 14%) with G gamma (average 40.5%) and A gamma T chains (average 59.5%). A large deletion of 18 to 23 kb was present with a 5' breakpoint within a 670-bp segment of DNA between the HpaI and NcoI restriction sites 5' to the delta globin gene, and a 3' breakpoint between the BamHI and HpaI restriction sites located some 9 to 13 kb 3' to the beta globin gene. This deletion is different from those present in other types of G gamma A gamma(delta beta)zero- thalassemia. The similarity of the hematological expression of these delta beta-thalassemic conditions which have somewhat comparable 5' breakpoints supports the idea that an important fetal hemoglobin- controlling region lies between the psi beta and delta globin genes.     

Laotian (delta beta) degree-thalassemia: molecular characterization of a novel deletion associated with increased production of fetal hemoglobin

We have identified and molecularly characterized a novel deletion in the beta-globin gene cluster that increases fetal hemoglobin (HbF) synthesis in a 24-year-old Laotian man who is heterozygous for this mutation. The patient is asymptomatic with a mild anemia, hypochromia, and microcytosis (Ht = 39%, MCH = 22.8 pg, MCV = 71 fl), normal levels of HbA2 (3.0%) and 11.5% HbF (G gamma A gamma ratio 60 to 40), with heterocellular distribution (52% F cells). Extensive restriction endonuclease mapping defined the 5' breakpoint within the IVS II of the delta-globin gene, between positions 775 to 781 very similar to the 5' breakpoint of the Sicilian delta beta-thalassemia. However, the 3' breakpoint was localized between two Pst I sites 4.7 kb 3' of the beta- globin gene, thus ending about 0.7 kb upstream from the 3' breakpoint of the Sicilian delta beta-thalassemia. This results in a 12.5 kb deletion of DNA. It is of interest that the 5' breakpoint of the deletion residues within an AT-rich region which has been proposed as a specific recognition signal for recombination events, while the 3' breakpoint lies within a cluster of L1 repetitive sequences (formerly known as Kpn I family repeats). The presence of the 3' breakpoints of several other deletions within this region of L1 repeats also suggests that such sequences might serve as hot spots for recombination and eventually lead to thalassemia deletions. The similarity of the 5' and 3' breakpoints of these delta beta-thalassemias underscores the putative regulatory role of the deleted and juxtaposed sequences on the expression of the gamma-globin genes in adult life.     

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.     

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.     

Hereditary persistence of fetal hemoglobin or (delta beta)o- thalassemia: three types observed in South-Chinese families

Hematological and hemoglobin composition data, and results from extensive gene mapping, using a battery of restriction enzymes and probes, have been used to distinguish different types of hereditary persistence of fetal hemoglobin (HPFH) (or delta beta-thal) among three Chinese families from the southern part of China. The first (Family Z) is an A gamma-(delta beta)+-HPFH without a detectable deletion and may be the same as, or similar to, that described by Farquhar et al (Am J Hum Genet 35:611, 1983). The second (Family C) resembles a G gamma(A gamma delta beta)o-thalassemia and is characterized by a large deletion of DNA originating 3' to the G gamma globin gene and extending beyond sequences recognized by the pRK28 probe. Data from various digests indicate possible differences in the 3' end of the deletion when compared with data for some other types of G gamma(A gamma delta beta)o- thalassemia, described by Trent et al (Br J Haematol 57:279, 1984). The third (Family Zh) concerns a G gamma A gamma(delta beta)+-HPFH, which is characterized in heterozygotes by a fetal hemoglobin level of 20% to 25% with a G gamma value averaging 60% and by the absence of any DNA deletion detectable by extensive gene mapping analyses. The C----G mutation at position 202 5' to the G gamma globin gene [characteristic for the high G gamma-(delta beta)+-HPFH (Proc Natl Acad Sci USA 81:4894, 1984; Blood 64:1292, 1984)] was absent, but the Xmn I site at position 158 5' to the G gamma globin gene [characteristic for a modest increase in G gamma values and thus and increased G gamma to A gamma ratio (Blood)] was present. No indication has yet been obtained explaining the elevation in both G gamma and A gamma chains; haplotyping showed that the chromosome carrying this G gamma A gamma(delta beta)+ determinant is unusual among the Chinese population.     

A greater than 200 kb deletion removing the entire beta-like globin gene cluster in a family of Irish descent.

We describe a new deletional form of gamma delta beta-thalassemia segregating in two generations of a family of Irish descent. Affected family members present with a beta-thalassemia minor phenotype, normal Hb A2 and Hb F levels. Genomic blotting analyses on DNA from affected family members show heterozygosity for a large deletion beginning at least 15 kb upstream of the 5' endpoint of the gamma delta beta-thalassemia-1 deletion, extending through the entire beta-like globin gene cluster, and continuing for at least 10 kb beyond the 3' endpoint of the deletion associated with the Spanish form of delta beta 0-thalassemia. This deletion is among the largest described so far, and removes at least 205 kb encompassing the entire beta-like globin gene cluster on chromosome 11.     

The delta beta crossover region in Lepore boston hemoglobinopathy is restricted to a 59 base pairs region around the 5'' splice junction of the large globin gene intervening sequence

Genomic DNA from a hemoglobin (Hb) Lepore Boston (delta 87 Gln beta 116 His) homozygote of Southern Italian origin has been studied in order to map the fusion point between the delta and beta genes. An Ava II restriction endonuclease recognition sequence, located 12 base pairs (bp) downstream from the 5' end of the beta gene large intervening sequence, has been taken as marker of the beta-like portion of the fusion gene. This site was present even in the delta beta gene, allowing the localization of the crossover area to a 59-bp region extending from the first nucleotide of the Leu codon in position 88 to the 11th nucleotide of the large intervening sequence. The analysis of the DNA restriction polymorphisms in the gamma delta beta globin gene region provides evidence that a single mutational event originated the Lepore delta beta genes, at least in the Italian population.     

Italian type of deletional hereditary persistence of fetal hemoglobin

We report a new type of deletion of the beta globin gene cluster in the Italian population that confers a phenotype of hereditary persistence of fetal hemoglobin (HPFH) to the carriers. This deletion begins approximately 5 kilobases (kb) 5' to the delta globin gene and ends approximately 30 kb 3' to the beta globin gene, in close proximity to the 3' end of an Indian HPFH. In all four previously described HPFH, a repetitive Alu I region 5' to the delta globin gene is largely or completely deleted; the 5' end of the new HPFH is consistent with this common feature. In addition, the finding that Italian and Indian HPFHs, as reported for other groups of deletions, have very close 3' ends, strengthens the idea that common mechanisms may operate in generating these deletions. Finally, we show that, in spite of similar 5' breakpoints, the deletion of Spanish delta beta(0)-thalassemia is at least 8 kb longer than that of Negro HPFH type I, thus ruling out the hypothesis that the overall extent of the deletion might influence the level of gamma globin chain synthesis.     

Increased expression of the G gamma and A gamma globin genes associated with a mutation in the A gamma enhancer

We have previously described a unique type of delta beta-thalassemia in a Chinese family characterized by increased expression of the G gamma and A gamma fetal globin genes in the absence of a large deletion in the beta-globlin gene cluster. Our earlier study of the beta-globin gene on this delta beta-thalassemia chromosome showed a promoter mutation in the TATA box. In this report, we describe the results of our study of the fetal globin domain of this delta beta-thalassemia chromosome. We have cloned a 13-kb DNA fragment that includes the G gamma and the A gamma genes and the 3' A gamma enhancer element of this delta beta-thalassemia chromosome. DNA sequence analysis of the G gamma and A gamma-globin genes including their promoters did not show any mutations, but analysis of the putative enhancer element downstream from the A gamma-globin gene showed a C to T substitution 2,401 nucleotides downstream from the A gamma cap site. We performed DNA linkage analysis to determine if this mutation is unique to this chromosome or represents a common polymorphism. Our linkage analysis showed that this mutation is not a common polymorphism and that it is also not an intrinsic part of the haplotype of the chromosome on which it was found. We also studied the interaction of nuclear proteins from erythroid and nonerythroid cells with the DNA sequences surrounding this mutation. We have shown by in vitro DNase I footprinting that this mutation falls within a region that is occupied by a novel DNA-binding protein that binds to this site in nuclear extracts from erythroid, but not nonerythroid cells. The binding of this nuclear protein to DNA appears to be dependent on GATA-1 binding to an adjacent GATA-1 site. We have also developed a new functional assay to compare the activity of the normal and mutant A gamma enhancer elements in erythroid cells. Analysis of the activity of the mutant enhancer shows that the mutation completely eliminates all enhancer activity in this assay. These findings suggest that this mutation of the A gamma enhancer on a chromosome that carries a partially inactivated beta-globin gene may be responsible for the increased expression of both gamma-globin genes seen in this condition.     

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.     

Rapid diagnosis of beta-thalassemia mutations in Chinese by naturally and amplified created restriction sites.

We developed a rapid and simple method to diagnose the molecular defects of beta-thalassemia in Chinese patients. This method involves the selective amplification of a DNA fragment from human beta globin gene with specific oligonucleotide primers, followed by digestion with restriction enzymes that recognize artificially created or naturally occurring restriction sites. To detect the 4-nucleotide deletion of codon 41-42, we introduced a single mismatch nucleotide into the 3' end of the upstream primer to create an artificial Taq I restriction site. With a similar approach, an artificial Rsa I site was generated to detect the nucleotide 654 mutation (C-->T) of IVS-2, and Alu I restriction site was created to detect the codon 17 mutation (A-->T), and EcoRI restriction site was created for the -28 mutation (A-->G), a Rsa I restriction site was created for the nucleotide 5 mutation (G-->C) of IVS-1, and a Spe I restriction site was created to distinguish the codon 71 (+T) and codon 71/72 (+A) mutations from a normal sequence. The other eight rare mutations that occur in the genes of the Chinese people naturally create or abolish restriction sites. Using this kind of approach, we are able to provide a simple, rapid, accurate, and nonradioactive method to detect the genetic defects of beta-thalassemia in the Chinese population. It should be used not only for routine screening but also for prenatal diagnosis.     

Two novel beta-thalassemia mutations in the 5' and 3' noncoding regions of the beta-globin gene.

Two novel beta-thalassemia mutations are described. The first mutation, found in an Italian family, is a G----A substitution in nucleotide (nt) +22 relative to the beta-globin gene Cap site. This mutation creates a cryptic ATG initiation codon, the utilization of which for translation would result in premature termination 36 bp 3' downstream. The second mutation, found in an Irish family, is a T----C substitution in nt +1570, or 12 bp 5' upstream of the AATAAA polyadenylation signal in the 3' noncoding region. It is postulated that this mutation leads to destabilization of the encoded beta-globin mRNA.     

Molecular characterization of a high A2 beta thalassemia by direct sequencing of single strand enriched amplified genomic DNA

Two families, one of Anglo-Saxon-Dutch descent, and the other, West Indian black, have an atypical beta thalassemia characterized by an unusually high level of Hb A2 in the heterozygous state. Restriction endonuclease mapping showed a deletion of about 1.35 kilobase (kb) in the 5' region of the beta globin gene. Direct sequencing of a specific region of genomic DNA amplified by a new modification of the polymerase chain reaction defined the deletion to be 1,393 base pairs (bp) and to be the same in both families. The deletion extends from 485 bp 5' to the mRNA CAP site to the middle of the second intervening sequence. This deletion, together with three others previously described that remove the 5' end of the beta gene but leave the delta gene intact, are all associated with unusually high levels of Hb A2 in the heterozygous state.     

Molecular comparison of delta beta-thalassemia and hereditary persistence of fetal hemoglobin DNAs: evidence of a regulatory area?

The hematological phenotypes of several Mediterranean patients with delta beta-thalassemia and hereditary persistence of fetal hemoglobin have been characterized. Although clinical and hematological characteristics are essentially superimposable in all heterozygous delta beta-thalassemics, these patients show typical G gamma/A gamma ratios in their Hb F, ranging from approximately 0.07 in Sardinian to approximately 0.15 in Sicilian and approximately 0.35 in Spanish patients. A gamma Sardinian-(isoleucine-75 leads to threonine) is found in Spanish patients and accounts for all of the A gamma production in heterozygotes, indicating that persistent production of gamma chains occurs cis to the delta beta-thalassemia gene. The molecular heterogeneity of these conditions is demonstrated by restriction enzyme mapping of DNA; Sicilian and Calabrian patients show a deletion starting from the delta-globin intron and extending several kilobases 3' to the beta-globin gene; in Spanish patients the deletion starts approximately 2-3 kilobases 5' to the delta-globin gene and extends well beyond the beta-globin gene. Comparison of these deletions with previously described ones in Negro and in a new Southern Italian case of hereditary persistence of fetal hemoglobin suggests that the deletion of a region centered at a cluster of repetitive sequences approximately 3.5 kilobases 5' to the delta-globin gene may be critical for the persistent expression of high levels of gamma-globin in hereditary persistence of fetal hemoglobin compared to delta beta-thalassemia. The concept that the deletion or mutation of specific areas (rather than nonspecific changes brought about by large deletions in the globin cluster) is important in determining the persistent expression of gamma-globin genes is supported by the finding of a nondeletion type of delta beta-thalassemia in Sardinians.     

Beta-thalassemia intermedia due to two novel mutations in the promoter region of the beta-globin gene

Two novel beta-thalassemia mutations affecting the promoter region of the beta-globin gene are described. The first mutation, found in a Moroccan family, is a G-->A substitution at position -190 relative to the beta-globin gene Cap site. The second, found in an Algerian patient, is a G-->C substitution at position -56 relative to the beta-globin Cap site. These two mutations occur in a region (-50 to -300) where promoter elements important for differential control of gene expression have been described and lead to beta-thalassemia intermedia in association with a beta(0)-thalassemia mutations.     

Concordance of a point mutation 5' to the G gamma globin gene with G gamma beta +. Hereditary persistence of fetal hemoglobin in the black population

Hereditary persistence of fetal hemoglobin (HPFH) is a genetically heterogeneous and clinically benign condition characterized by persistent expression of fetal hemoglobin (Hb F) into adulthood. In the G gamma beta + type, no major deletions in the globin gene cluster occur; adult heterozygotes produce approximately 20% Hb F, which results from overproduction of G gamma chains, with no apparent increase in production from the adjacent A gamma gene. We have recently described a point mutation 202 base pairs 5' to the cap site of the G gamma gene in an individual with G gamma beta + HPFH. This mutation abolishes a normal ApaI restriction endonuclease site, and thus can be detected by blotting of genomic DNA. We present here further data on the ApaI mutation: (1) It occurs in six of seven families with G gamma beta + HPFH. (2) In three families, detailed haplotype analysis using 11 polymorphic restriction sites in the beta globin cluster has been done. The two that carry the missing ApaI site are identical but the third, which has a normal ApaI pattern, differs from the other two in at least two sites, one of which is a new polymorphic Nco I site between the delta and beta globin genes. This suggests the possibility of a different HPFH mutation in the third family. (3) The haplotype of the G gamma beta + HPFH chromosome carrying the ApaI mutation is different from that of 108 beta A chromosomes of black individuals that have been tested. (4) The G gamma ApaI site is normal in 61 beta A and 109 beta S alleles from non-HPFH black individuals, including 22 who share the same haplotype for the intragenic G gamma, A gamma HindIII polymorphisms. These data add support to the possibility that the -202 mutation is actually causative of the G gamma beta + HPFH phenotype.     

Beta+-thalassemia in cis of a sickle cell gene: occurrence of a promoter mutation on a beta s chromosome

An atypical sickle cell trait with a very low level of hemoglobin S and features of heterozygous beta-thalassemia was recently described. In vitro globin chain synthesis strongly suggested the presence of the two abnormalities on the same chromosome. We report the corresponding beta S-thal gene. DNA sequence revealed a C----T base substitution in the distal promoter element CACCC, at position-88 from the cap site, in addition to the expected GAG----GTG mutation responsible for the structural variant (beta 6 Glu----Val). Reticulocyte mRNA titration and transient assay of the mutant gene in COS cells showed a defect in beta- mRNA production. Restriction haplotype and DNA sequence analyses revealed that the doubly mutated gene is associated with haplotype 19 (or Benin/Algeria haplotype). In particular, we found the (AT)9(T)4 repeated sequences specifically encountered 5' to the beta S gene of Benin Algeria type. These results support the view that the beta S-thal gene resulted from an independent thalassemic mutation having occurred on a beta S chromosome rather than (a) from a beta S mutation having altered a beta-thalassemic gene or (b) from a recombination event between two chromosomes, each carrying one of the mutations.     

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.