E. Baysal

α‐Thalassaemia in the population of Cyprus

We have determined the α‐thalassaemia (α‐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 α‐thal alleles were present; the ‐α(3.7 kb) α‐thal‐2 and the —MED‐1α‐thal‐1 were most frequently seen; —MED‐II and ‐(α)20.5 deletions occurred at considerably lower frequencies. About 15% of all chromosomes carried a non‐deletional α‐thal‐2 allele; of these the 5 nucleotide (nt) deletion at the first intervening sequence (IVS‐I) donor splice site was present in ˜ 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 α‐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 ˜ 22%) in the 12 patients with the α5ntα/—MED‐I combination. One patient with the same form of Hb H disease but with an additional β‐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.

Types of Thalassemia Among Patients Attending a Large University Clinic in Kuala Lumpur, Malaysia

We have identified the beta-thalassemia mutations in 59 patients with thalassemia major and 47 patients with Hb E-beta-thalassemia, and the deletional and nondeletional alpha-thalassemia determinants in 23 out of 24 patients with Hb H disease. All persons were attending the Haematology Clinic at the National University of Malaysia in Kuala Lumpur (Malaysia). Most patients (76) were of Malay descent, while 52 patients were Chinese, and two came from elsewhere. The most frequently occurring beta-thalassemia alleles among the Malay patients were IVS-I-5 (G----C) and G----A at codon 26 (Hb E), while a few others were present at lower frequencies. The Chinese patients carried the mutation characteristic for Chinese [mainly codons 41/42 (-TTCT) and IVS-II-654 (C----T)]; Malay mutations were not observed among Chinese and Chinese mutations were virtually absent in the Malay patients. The large group of patients with Hb E-beta-thalassemia and different beta-thalassemia alleles offered the opportunity of comparing hematological data; information obtained for patients with Hb E-beta-thalassemia living in other countries was included in this comparison. Twenty-three patients with Hb H disease carried the Southeast Asian (SEA) alpha-thalassemia-1 deletion; 13 had the alpha CS alpha (Constant Spring) nondeletional alpha-thalassemia-2 determinant, while the deletional alpha-thalassemia-2 (-3.7 or -4.2 kb) was present in 10 subjects. The --/alpha CS alpha condition appeared to be the most severe with higher Hb H values. Both deletional and nondeletional types of alpha-thalassemia-2 were seen among Malay and Chinese patients.

Molecular characterization of β-thalassemia in Czechoslovakia

SummaryWe have identified different β-thalassemia mutations in 93 members of 34 families of Czech or Slovakian descent using gene amplification, hybridization with specific 32P-labeled oligonucleotide probes, sequencing of amplified DNA, and gene mapping. The G→A mutation at IVS-I-1 was found in 18 families; other Mediterranean mutations were IVS-II-1 (G→A), IVS-II-745 (C→G), IVS-I-110 (G→A), and codon 39 (C→T); these were present in 9 additional families. The G→T mutation at codon 121, known to cause Heinzbody β-thalassemia, was present in 3 families, and the frameshift at codons 82/83 (-G), first described in the Azerbaijanian population, in 2 families. A newly discovered allele was a frameshift at codons 38/39 (-C). One β-thalassemia allele was incompletely characterized. We observed in 2 families a T→C mutation at position +96 UTR (untranslated region) relative to the termination codon; this mutation likely is a rare polymorphism, α-Thalassemia was rare; only one person carried the -α3.7 heterozygosity, and one other had a yet to be identified α-thalassemia-1, while seven had the αααanti 3.7 triplication.

HEMOGLOBINOPATHIES IN THE UNITED ARAB EMIRATES

The use of modern DNA techniques enabled us to characterize and identify 44 distinct beta-thal mutations and nine alpha-thal genotypes in the UAE population. All of the beta-thal mutations were severe beta+ or beta0 types resulting in transfusion-dependent phenotypes. Furthermore, a large number of alphaT alleles in the alpha-thal carriers and in patients with Hb H disease, accentuate the importance of Hb H disease as a public health problem. The overall data presented here will be useful for genetic counseling, pre-marital carrier screening and the establishment of a comprehensive prenatal diagnosis program.

Molecular characterization of β-thalassemia in Azerbaijan

We have analyzed the β-thalassemia mutations in 99 chromosomes of 49 adults with β-thalassemia major and of one with Hb S-β-thalassemia, who are regular patients at a large hematology clinic in Bakü, Azerbaijan. A total of 20 different mutants were identified; three [frameshift at codon 8 (-AA); IVS-II-I (G→A); IVS-I-110 (G→A)] were present in about two-thirds of all chromosomes. Most alleles are the same as found in Mediterranean populations; a few have an Asian origin or come from Kurdistan, Lebanon, Saudi Arabia, or a black population. One mutant [frameshift at codons 82/ 83 (-G)] might be specific for the Azerbaijanian population. Nearly all patients were transfused, which made quantitation of Hb F impossible; highGγ values were present in the Hb F of those patients whose β-thalassemia chromosome carried the C → T mutation at position — 158 in the promoter of the Gγ-globin gene.

Hb H disease caused by a homozygosity for the AATAAA→AATAAG mutation in the polyadenylation site of the α2-globin gene : hematological observations

We have identified 7 patients with Hb H disease as homozygotes for a mutation in the polyadenylation site (AATAAA-->AATAAG) and have compared their hematological data with those of Hb H patients having other types of alpha-thalassemia determinants. All 7 patients exhibited moderate anemia with microcytosis and hypochromia being similar to that observed in the other patients. Relatives with a heterozygosity for this mutation are borderline microcytic and hypochromic without a significant anemia but with a low in vitro alpha/beta chain synthesis ratio. Analyses of the hemoglobin components identified low levels of Hb A2 and Hb H that were comparable to those found in other patients with Hb H disease; the level of the zeta-chain was low (average 0.14%).

β-Thalassehia 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.

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

Summary. In 1991 we reported the identification of two deletional α‐thalassaemia‐2 determinants (— 3.7 kb and — 4.2 kb) and one nondeletional α‐thalassaemia‐2 determinant (Hb Koya Dora α2 codon 142, TAA→TAA) 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 α‐thalassaemia‐2 because of low levels of Hb S (<28%) in some Hb S heterozygotes with a simple α‐thalassaemia‐2 heterozygosity (—α/αα). This abnormality has now been identified as a G→A mutation at IVS‐I‐117 of the α1‐globin gene (acceptor splice site) which makes this gene nonfunctional. Its frequency was established at ˜6% which raises the total frequency of α‐thalassaemia determinants in this population to ˜60%. Subjects with a deletional α‐thalassaemia‐2 and the newly discovered α1 acceptor splice junction mutation in trans appear to have an α chain deficiency similar to that of an α‐thalassaemia‐2 homozygote (—α/—α). An additional change (C→G) at the Cap —4 site was observed in six α1‐ and one α2‐globin genes: this polymorphism is not associated with a decrease in α chain synthesis and is not linked to the IVS‐I‐117 (G→A) mutation.

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

Summary. We have collected haematological, haemoglobin (Hb) and DNA sequence data for 29 patients with a homozygosity for the IVS‐I‐6 (TC) 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 α‐thalassaemia‐2 (α‐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 Gγ values and the CT mutation at position – 158 in the Gγ 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 Gγ and Aγ 5 flanking regions, the second intervening sequence (IVS‐II), and the 5 β‐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 Gγ and Aγ 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 β‐globin gene cluster in mediating γ‐globin gene expression in patients with this type of β‐thal.

Distribution of β-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).