Hb Costa Rica or alpha 2 beta 2 77(EF1)His --> Arg: the first example of a somatic cell mutation in a globin gene

We have identified a minor hemoglobin component (approximately 5%) in the blood of a healthy Costa Rican female, but not in her mother and two brothers (father not studied), that has an His --> Arg replacement at position beta 77 (Hb Costa Rica). No other amino acid replacements were observed and no beta- or gamma-chain-like peptides were present. Hb Costa Rica has abnormal stability. Sequence analyses of numerous polymerase chain reaction (PCR)-amplified segments of DNA that contain exon 2 of the beta gene failed to identify a CAC --> CGC (His --> Arg) mutation. The same was the case when cDNA was sequenced, indicating that a beta-Costa Rica-mRNA could not be detected with this procedure. Gene mapping of genomic DNA with Bg/II, BamHI, and HindIII gave normal fragments only and with the same intensity as observed for the fragments of a normal control. The quantities of the beta chain variants Hb J-Iran and Hb Fukuyama with related mutations at beta 77 vary between 30% and 45% in heterozygotes, whereas that of Hb F-Kennestone with the same His --> Arg mutation but in the G gamma-globin gene, is a high 40%-45% (as percentage of total G gamma) in a heterozygous newborn. These different observations exclude a heterozygosity of the A --> G mutation at codon beta 77, as well as a deletion comparable to that of Hbs Lepore or Kenya, or a beta-globin gene duplication, and point to a nontraditional inheritance of Hb Costa Rica. Allele-specific amplification of cDNA with appropriate primers identified the presence of a low level of mutated mRNA in the reticulocytes of the patient, which was confirmed by dotblot analysis of the same material with 32P-labeled probes. Comparable amplification products were not observed in genomic DNA. The A --> G mutation apparently occurred in a somatic cell at a relatively early stage in the development of the hematopoietic cell system, and Hb Costa Rica accumulated through rapid cell divisions in patchy areas in the bone marrow (somatic mosaicism). An unequal distribution of Hb Costa Rica over the red cells supports this possibility.

Hb Bibba or alpha 2 136(H19)Leu-->Pro beta 2 in a Caucasian family from Alabama

Several members of a large Caucasian family who presented with a congenital Heinz body hemolytic anemia were found to be carriers of the unstable Hb Bibba or alpha 2 136(H19)Leu-->Pro beta 2. Identification by protein analysis was hampered by the instability of the variant which complicated its isolation from shipped blood samples. Moreover, the detection of the CTG-->CCG mutation at codon 136 of the alpha 2 gene required the substitution of dGTP by dITP during the DNA sequencing process to prevent the occurrence of secondary structures and compressions in the sequencing gel. The first Hb Bibba heterozygote, characterized in 1968 (1), is believed to be a member of this family. The clinical expression of the disease is surprisingly variable.

alpha-Thalassaemia in the population of Cyprus

We have determined the alpha-thalassaemia (alpha-thal) determinants in 78 patients with Hb H disease from Cyprus; 25 were Turkish Cypriots and 53 were Greek Cypriots. Four deletional and three non-deletional alpha-thal alleles were present; the -alpha(3.7 kb) alpha-thal-2 and the --MED-I alpha-thal-1 were most frequently seen; --MED-II and -(alpha)20.5 deletions occurred at considerably lower frequencies. About 15% of all chromosomes carried a non-deletional alpha-thal-2 allele; of these the 5 nucleotide (nt) deletion at the first intervening sequence (IVS-I) donor splice site was present in approximately 8% of all chromosomes. Two types of polyadenylation signal (poly A) mutations were observed. No striking frequency differences were seen between Greek and Turkish Cypriot patients. Combinations of the various types of alpha-thal resulted in eight different forms of Hb H disease. The phenotypes were comparable except for great variations in the level of Hb H which was highest (average approximately 22%) in the 12 patients with the alpha 5nt alpha/--MED-I combination. One patient with the same form of Hb H disease but with an additional beta-thal (IVS-I-110,G-->A) heterozygosity had a most severe microcytosis and hypochromia with < 1% Hb H. Variations in the level of Hb H might correlate with the severity of the disease, although this was not evident from the haematological data.

Factors associated with hypochromia and microcytosis among high school students in the southeastern United States

We studied hematologic findings in 617 apparently healthy Georgia elementary, middle, and high school students, aged 10 to 19 years, and examined the influence of several parameters (race, sex, iron status, and genetic hemoglobin [Hb] abnormalities) on hypochromia and microcytosis, with or without anemia. Fourteen students (2%) (6 male, 8 female; 4 white, 10 black) were found to be anemic (Hb < 11.8 g/dL in boys or < 11.3 g/dL in girls). Hypochromia (mean corpuscular Hb < 25 pg) with or without microcytosis (mean corpuscular volume < 78 fL) was found in 26 students (4%). Iron deficiency was the main associated factor in white students, but in blacks genetic Hb abnormalities, especially alpha-thalassemia trait, were other predisposing factors. The overall prevalence of iron deficiency (serum ferritin < or = 12 ng/mL) was 32.4% in the entire sample population, 30.5%, among blacks, and 33.2% among whites.

Beta-thalassemia alleles and unstable hemoglobin types among Russian pediatric patients

A recently initiated collaboration between Russian and American institutions has resulted in the characterization of several known or new beta-thalassemia alleles and unstable hemoglobin types. Nine known beta-thalassemia alleles were present which have also been found in Mediterranean, East Asian, and Black populations; the possibility of independent mutations for some of the rare alleles should be considered. Hb Durham-N.C./Brescia with a codon 114 (CTG-->CCG; Leu-->Pro) change was present in six members of two families. This condition and two new variants have the characteristics of a dominant type of beta-thalassemia heterozygosity with moderate anemia, Heinz body formation, splenomegaly, etc. One new beta-thalassemia allele is a frame-shift at codon 124 (-A), while another is characterized by the introduction of an extra proline residue (codon: CCA) between residues Thr (beta 123) and Val (beta 126) to give the sequence -Thr-Pro-Pro-Pro-Val-.

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.

Distribution of beta-thalassemia mutations in three Asian Indian populations with distant geographical locations

We have identified the beta-thalassemia alleles in 47 pediatric patients with transfusion-dependent thalassemia major from a clinic in New Delhi and in 105 heterozygous relatives. Surprisingly, only five mutations were present in 94 beta-thalassemia chromosomes with frequencies from 10 to 32%. This observation greatly facilitated the initiation of a prenatal diagnostic program. Similar studies were conducted for seven Asian Indian patients from Calgary, Canada, seven Asian Indian patients from Durban, South Africa, and from heterozygous relatives, and persons with a beta-thalassemia trait who were not related. Besides beta-thalassemia alleles, common to Asian Indian beta-thalassemia patients, some unexpected alleles were observed in the patients from South Africa, including a newly discovered frameshift at codon 15 (-T).

Possible factors influencing the haemoglobin and fetal haemoglobin levels in patients with beta-thalassaemia due to a homozygosity for the IVS-I-6 (T-->C) mutation

We have collected haematological, haemoglobin (Hb) and DNA sequence data for 29 patients with a homozygosity for the IVS-I-6 (T-->C) mutation with the intention of identifying factors contributing to the observed variability in the severity of the disease. None of the patients had received blood transfusion therapy for at least 6 months prior to the study. Hb levels varied from 5.0 to 9.9 g/dl. Patients with high Hb F (more than 1.5 g/dl or > 20%) had high total Hb levels (7.5-9.7 g/dl) but some with low Hb F also had high total Hb levels; two had a concomitant alpha-thalassaemia-2 (alpha-thal-2) heterozygosity. An inverse correlation between the Hb F and Hb A2 levels was observed. The majority of the patients were homozygous for haplotype VI (49/58 chromosomes) but haplotypes IV (2/58) and VII (7/58) were also present. The only haplotype IV homozygote had high Hb F levels with high G gamma values and the C-->T mutation at position -158 in the G gamma promoter, while both high and low Hb F levels were observed among patients with haplotypes VI and VII. Analysis of sequence variations in regulatory regions included the 5' hypersensitive sites (HS) 4. 3 and 2 of the locus control region (LCR), the G gamma and A gamma 5' flanking regions, the second intervening sequence (IVS-II), and the 5' beta-globin gene region in two patients with high Hb F (one homozygote each for haplotypes VI and IV), and in two patients with low Hb F levels (one homozygote each for haplotypes VI and VII). Haplotype specific differences were observed in the LCR 5' HS-2 and in the G gamma and A gamma flanking and IVS-II regions; however, no differences were present between the low and high Hb F-producing haplotype VI chromosomes, suggesting a major role for factors which are not linked to the beta-globin gene cluster in mediating gamma-globin gene expression in patients with this type of beta-thal.

Sickle cell anemia, sickle cell beta-thalassemia, and thalassemia major in Albania: characterization of mutations

We have analyzed the hemoglobin abnormalities in nearly 50 Albanian patients with a significant hemoglobinopathy and included 37 relatives in this study. Sickle cell anemia (SS) is a common disorder; all 15 sickle cell anemia patients had the complications expected for this disease. The beta S haplotype was type 19 (Benin); alpha-thalassemia-2 was rare. Three beta-thalassemia alleles (IVS-I-110, G-->A; codon 39, C-->T; IVS-I-6, T-->C) were present in nearly 85% of the beta-thalassemia alleles; their frequencies were intermediate between those observed in the populations of neighboring countries. A few rare mutations were also found, which might have originated in India, Turkey, Macedonia, and Greece. Nearly all patients with Hb S-beta-thalassemia had the IVS-I-110 (G-->A) mutation. The frequencies of 11 beta-thalassemia mutations in 17 mostly Mediterranean countries have been reviewed.

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 alpha-thalassemia determinants, beta-thalassemia alleles, and beta S haplotypes among Kuwaiti Arabs

Using amplification, allele-specific oligonucleotide (ASO) hybridization and DNA sequencing we have documented the molecular basis of 64 alpha- and 123 beta-thalassemia (thal) chromosomes, and the haplotypes of 18 beta S chromosomes from patients followed in three hospitals in Kuwait. Of the 30 chromosomes from 15 patients with Hb H disease, 26 (86.7%) carried the polyadenylation (poly A) signal mutation (AATAAA-->AATAAG) in the alpha 2-globin gene, 3 (10%) had the -alpha (3.7 kb) deletion, and 1 (3.3%) had the pentanucleotide deletion in the 5' IVS-I splice junction (alpha-5nt alpha). As many as 12 different beta-thal mutations were identified; 6 Mediterranean alleles [IVS-II-1 (G-->A), IVS-I-6 (T-->C), codon (CD) 39 (C-->T), IVS-I-110 (G-->A), CD 8 (-AA), and IVS-I-1 (G-->A)] were present in 79 (64.2%) of the chromosomes tested. Four East Indian alleles [IVS-I-5 (G-->C), IVS-I 3' end -25 nt deletion, CDs 8/9 (+G), and 619-bp deletion] were found in 31 (25%), and the two Kurdish/Iranian alleles [CD 44 (-C) and CDs 36/37 (-T)] were found in 13 (10.6%) chromosomes. Fourteen beta S chromosomes carried haplotype No. 31 (Saudi Arabia/India); 3 had haplotype No. 19 (Benin), and 1 was a hybrid with haplotype No. 31-specific characteristics in the locus control region hypersensitive site-2 (LCR-HS-2), and haplotype No. 19-specific mutations in the 5' flanking region of the G gamma-promoter. The patient homozygous for haplotype No. 19 was a Jordanian, while the others were Kuwaiti Arabs. The latter appear to be fairly homogeneous in terms of the prevalent alpha-thal determinants and beta S-haplotypes, but there is considerable heterogeneity of their beta-thal alleles. This has implications for genetic counseling and prenatal diagnosis programs.

The T-->C mutation at position +96 of the untranslated region 3' to the terminating codon of the beta-globin gene is a rare polymorphism that does not cause a beta-thalassemia as previously ascribed

We have observed a T-->C mutation at position +96 of the untranslated region 3' to the terminating codon of the beta-globin gene in members of two Czech families and one black family. Data from initial studies suggested that this change was the cause of a beta-thalassemia, but continued analyses have provided convincing evidence that this mutation is a simple polymorphism.

Polymorphic pattern of the (AT)X(T)Y motif at -530 5' to the beta-globin gene in over 40 patients homozygous for various beta-thalassemia mutations

Nucleotide sequence analysis of the 5' beta-globin gene flanking region has been carried out for numerous homozygous beta-thalassemia patients with different mutations and of various ethnic backgrounds. Four different rearrangements were found associated with numerous beta-thalassemia mutations. The (AT)X(T)Y repeat motif at -530 showed polymorphic patterns among these patients as follows: All ten IVS-II-1 (G-->A) chromosomes and the two with the -87 (C-->G) mutation are associated with the (AT)9(T)5 rearrangement, while the 30 IVS-I-6 (T-->C), the 16 codon 39 (C-->T), the six codon 8 (-AA) chromosomes, and 12 chromosomes with different promoter mutations had the (AT)7(T)7 motif. Six chromosomes with the promoter mutation at position -29 (A-->G) had the (AT)8(T)6 motif, while an (AT)8(T)4 motif appears characteristic for two IVS-I-5 (G-->A and G-->T). No direct association between any of the (AT)X(T)Y arrangements and an increased gamma gene expression [G gamma and fetal hemoglobin (Hb F)] levels could be demonstrated, suggesting that variations in the (AT)X(T)Y motif are common polymorphisms.

Quantities of alpha Q chain variants in heterozygotes with and without a concomitant beta-thalassemia trait

We have analyzed the quantities of alpha x chain-containing hemoglobins (alpha 2 x beta 2 and alpha 2 x delta 2) in 14 heterozygotes for Hb Q-India [alpha 64(E13)Asp-->His] or Hb Q-Thailand [alpha 74(EF3)Asp-->His]; both amino acid replacements are the result of mutations in the alpha 1-globin gene. Five of these persons (three with Hb Q-India and two with Hb Q-Thailand) had an additional beta(0)-thalassemia heterozygosity. The average quantities for Hb Q + Hb Q2 in the four groups were 17.2% (alpha alpha Q/alpha alpha; beta A/beta A), 9.5% (alpha alpha Q/alpha alpha; beta A/beta(0) Th), 26.8% (-alpha Q/alpha alpha; beta A/beta A), and 16.95% (-alpha Q/alpha alpha; beta A/beta(0) Th). These variations can best be explained by a posttranslational control mechanism; an imbalance in the alpha A, alpha Q, and beta A chain ratio will favor the alpha 2 Q beta 2 formation when an alpha-thalassemia is present and will reduce its formation in the presence of a beta-thalassemia heterozygosity.

Binding of nuclear factors to the proximal and distal CACCC motifs of the beta-globin gene promoter: implications for the -101 (C-->T) 'silent' beta-thalassemia mutation

We have used the gel retardation assay to investigate the binding of nuclear proteins to the duplicated CACCC boxes in the beta-globin gene promoter region. The effect of beta-thalassemia mutations affecting both of these consensus sequences (the -88 C-->T and -101 C-->T mutations) were studied by using appropriate mutant oligonucleotides. Upon incubation with nuclear proteins from human erythroleukemia cells, the synthetic oligonucleotides containing single and/or duplicated CACCC box(es) generated five retarded bands. Bands B1 and B2 appeared to be highly specific complexes as determined by competition experiments whereas bands B3, B4 and B5 were nonspecific. The binding of the specific trans-acting factors was stable and could be competed out only by relatively high concentrations of competitor DNA. The proximal CACCC box (as in the -88N probe) appeared to be essential in the binding of nuclear proteins and a mutation at nt -88 (C-->T) abolished binding completely. In contrast, the distal CACCC box showed no binding activity either as normal (-101N) or as mutant (-101M). A full competition with the Sp1 oligonucleotide, even at low concentrations, suggested a high affinity binding to the Sp1 consensus sequence. The close similarities in the binding patterns of the labelled -88N, -88N/-101N and that of the labelled Sp1 probe add further credence to the possibility that bands B1 and B2 may be due to the Sp1 protein, a ubiquitously expressed trans-activator.

Hb Adana or alpha 2(59)(E8)Gly-->Asp beta 2, a severely unstable alpha 1-globin variant, observed in combination with the -(alpha)20.5 Kb alpha-thal-1 deletion in two Turkish patients

We have identified a severely unstable hemoglobin variant through sequencing of amplified DNA involving the alpha 1-globin gene; the mutation is located in codon 59 (CCG CAG) and results in a Gly-->Asp replacement. This amino acid substitution concerns a glycine residue at an internal position in the E helix, which is in close contact with a glycine residue of the B helix; introduction of the larger and charged aspartic acid residue greatly affects the stability of the molecule. This variant was present in association with a common alpha-thalassemia-1 deletion [-(alpha)20.5 kb] in two adults and caused a severe type of Hb H disease with anemia, low levels of Hb A2, increased zeta chain, and Hb Bart's. In vitro chain synthesis in reticulocytes showed a high specific activity of the variant alpha chain. Only a minute quantity of Hb H was present but instead about 10% of Hb Bart's was observed. The increased synthesis of gamma chains was likely due to specific characteristics of a chromosome with haplotype #3, which was present in both patients. The same family was studied 18 years ago; the improved methodology presently available has led to a corrected diagnosis for these patients.

An IVS-I-117 (G-->A) acceptor splice site mutation in the alpha 1-globin gene is a nondeletional alpha-thalassaemia-2 determinant in an Indian population

In 1991 we reported the identification of two deletional alpha-thalassaemia-2 determinants (-3.7 kb and -4.2 kb) and one nondeletional alpha-thalassaemia-2 determinant (Hb Koya Dora alpha 2 codon 142, TAA-->TCA) in a tribal population in Central India (Gupta et al, 1991). Evidence was obtained at that time for the possible presence of an additional nondeletional alpha-thalassaemia-2 because of low levels of Hb S (< 28%) in some Hb S heterozygotes with a simple alpha-thalassaemia-2 heterozygosity (-alpha/alpha alpha). This abnormality has now been identified as a G-->A mutation at IVS-I-117 of the alpha 1-globin gene (acceptor splice site) which makes this gene nonfunctional. Its frequency was established at approximately 6% which raises the total frequency of alpha-thalassaemia determinants in this population to approximately 60%. Subjects with a deletional alpha-thalassaemia-2 and the newly discovered alpha 1 acceptor splice junction mutation in trans appear to have an alpha chain deficiency similar to that of an alpha-thalassaemia-2 homozygote (-alpha/-alpha). An additional change (C-->G) at the Cap -4 site was observed in six alpha 1- and one alpha 2-globin genes; this polymorphism is not associated with a decrease in alpha chain synthesis and is not linked to the IVS-I-117 (G-->A) mutation.

A mild type of Hb S-beta(+)-thalassemia [-92(C-->T)] in a Sicilian family

Hematological data are presented for an adult Sicilian patient with a mild Hb S-beta(+)-thalassemia caused by a C-->T mutation at position -92 of the beta promoter. This mutation was identified by sequencing of amplified DNA and was confirmed by dot-blot analysis with specific probes. A comparison of levels of Hb S and Hb A in Hb S-beta-thalassemia patients with different beta-thalassemia alleles showed great variations; the highest level of Hb A (45%) was recorded in the patient with Hb S-beta(+)-thalassemia [-92(C-->T)] and the lowest (approximately 13%) in patients with Hb S-beta(+)-thalassemia [IVS-II-745 (C-->G)]. Clinical severity is directly related to the level of Hb A present.

Beta-thalassemia mutations in the Portuguese; high frequencies of two alleles in restricted populations

We report the characterization of seven different beta-thalassemia mutations in 131 newly diagnosed Portuguese beta-thalassemia heterozygotes. Methodology included the detection of abnormal fragments by agar gel electrophoresis of PCR-amplified DNA fragments after digestion with specific restriction endonucleases, as well as hybridization with synthetic nucleotide probes and sequencing of amplified DNA. Four mutations, including the newly discovered TGG-->TGA change at codon 15, occurred in excess of 10% and accounted for some 90% of the beta-thalassemia alleles in this population. The geographical distribution is uneven; the TGG-->TGA mutation at codon 15 was primarily observed in the coastal region north of Lisbon, while the IVS-I-6 (T-->C) mutation was confined to the central part of the country.