Genetic heterogeneity of beta-thalassemia at Cukurova in southern Turkey.

Beta-thalassemia is the most common genetic abnormality causing health problems worldwide. Cukurova, in the southern part of Turkey, being on the Mediterranean, is in the thalassemic belt. Since there is no cure for the disease at present, the frequency of the mutation types of beta-thalassemia must first be identified to aid in clinical follow-up and prenatal diagnosis. Carriers identified during a screening survey and patients referred to our laboratory were studied for this purpose. After routine hematological analysis molecular screening was performed by the amplification refractory mutation system and DNA sequencing. The frequency of the common mutations were: IVS-I-110 (G-->A) 57.3%, IVS-I-1 (G-->A) 8.3%, codon 39 (C-->T) 6.4%, IVS-I-6 (T-->C) 5.7%, frameshift codon 8 (-AA) 5.7%, -30 (T-->A) 4.7%, IVS-II-1 (G-->A) 3.4%, IVS-II-745 (G-->C) 2.8%, and frameshift codon 5 (-CT) 1.1%. Some rare mutations (1%) such as frameshift codon 44 (-C) 0.7%, frameshift codons 74/75 (-C) 0.7%, IVS-1-5 (G-->C) 0.7%, frameshift codons 8/9 (+G) 0.4%, frameshift codons 36/37 (-T) 0.4%, frameshift codons 22/23/24 (-AAGTTGG) 0.4%, IVS-1-130 (G-->C) 0.4%, IVS-1-5 (G-->T) 0.2%, -28 (A-->C) 0.2%, codon 15 (TGG-->TGA) 0.2%, and frameshift codons 82/83 (-G) 0.2%, were detected by sequence analysis. The codon 15 (TGG-->TGA) and frameshift codons 82/83 (-G) mutations were seen in Turkey for the first time.

Genetic heterogeneity of beta-thalassemia in southeast Sicily.

In this study we have defined the spectrum of the beta-thalassemia mutations, the beta-thalassemia haplotypes, and the genotype-to-phenotype correlations in a large number of patients with different beta-thalassemia conditions. Seventeen different beta-thalassemia mutations were detected which included one chromosome each with Hb Dhonburi and Hb Lepore. Five alleles, namely, codon 39 (C-->T), IVS-I-110 (G-->A), IVS-I-6 (T-->C), IVS-II-745 (C-->G), and IVS-I-1 (G-->A), account for 90% of all beta-thalassemia mutations in 846 thalassemic chromosomes studied. Haplotyping for a large number of subjects showed that the five common mutations are linked to a few haplotypes. The presence of milder mutations, mainly IVS-I-6 (T C), in about 19% of our patients explains some of the clinical variables. Among the 37 patients with thalassemia of intermediate severity, only 6 were homozygous or compound heterozygous for two severe alleles. The type of beta-thalassemia is the main factor responsible for differences in the phenotypic expression of the disease in patients with Hb S-beta-thalassemia; patients with Hb S-beta(+)-thalassemia are less severely affected than those with Hb S-beta(0)-thalassemia. The five most frequent mutations have comparable distributions all over Sicily.

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-.

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.

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.

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.

Molecular characterization of beta-thalassemia in Azerbaijan.

We have analyzed the beta-thalassemia mutations in 99 chromosomes of 49 adults with beta-thalassemia major and of one with Hb S-beta-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; high G gamma values were present in the Hb F of those patients whose beta-thalassemia chromosome carried the C-->T mutation at position -158 in the promoter of the G gamma-globin gene.

Hb H disease in a Turkish family resulting from the interaction of a deletional alpha-thalassaemia-1 and a newly discovered poly A mutation.

We have analysed the alpha-globin gene defects present in several members of a large family from Southern Turkey. One deletional alpha-thalassaemia-1 (type MED-II) was found in 10 subjects: this deletion is in excess of 26.5 kb and includes all zeta- and alpha-globin genes. Besides the common types of deletional alpha-thalassaemia-2 (-3.7 kb and -4.2 kb) we observed a nondeletional alpha-thalassaemia-2 that results from an A----G mutation (AATAAA----AATGAA) in the polyadenylation signal of the alpha 2-globin gene: the same A----G replacement is present in the psi alpha l gene. The mutation must cause a considerable alpha-chain deficiency as is evidenced by the haematological data for five members with Hb H disease due to a compound heterozygosity for alpha-thalassaemia-1 (MED-II) and the newly discovered poly A mutation. Several members had additional beta-chain abnormalities (Hb S, Hb D-Los Angeles, beta-thalassaemia); the 11 persons with a Hb S heterozygosity and various alpha-globin gene defects (-alpha/alpha alpha; alpha T alpha/alpha alpha, - -/alpha alpha, -alpha/-alpha and - -/alpha T alpha) showed a decrease in the level of Hb S that was directly related to the severity of the alpha-chain deficiency.