Rare beta-thalassemia alleles in the Greek and Greek Cypriot populations.
Explore the source record for details and available documents.
Alleles↗
Biomedical subjects
E Kanavakis
Publications and source records attributed to E Kanavakis.
An alpha-thalassemic hemoglobinopathy: homozygosity for the HB Agrinio alpha 2-globin chain variant.
This report describes the first case of homozygosity for the Hb Agrinio [alpha 29(B10)Leu-->Pro] alpha 2-globin gene variant (codon 29, CTG-->CCG) in a Greek patient. At 12 months of age, the proband presented with a marked hypochromic, microcytic anemia, a very low level of Hb H (< 2.5%), rare Hb H inclusions, and a balanced alpha/non-alpha biosynthesis ratio. The mother had hematological findings and globin biosynthesis consistent with heterozygous beta-thalassemia, but paradoxically, red cell morphology demonstrated very rare Hb H inclusions. The father had mild microcytosis and hypochromia. Analysis of alpha- and beta-globin genotypes demonstrated that the patient was homozygous for the highly unstable Hb Agrinio variant, caused by a T-->C mutation in codon 29 of the alpha 2-globin gene. At the age of 13 years, the proband had a clinical phenotype compatible with mild thalassemia intermedia with moderate anemia (Hb 7-8 g/dL), normal growth and development, slight splenomegaly, and minimal bone changes, while Hb H and inclusion bodies were not detected.
Genetic Carrier Screening↗
Synthesized allosteric effectors of the hemoglobin molecule: a possible mechanism for improved erythrocyte oxygen release capability in hemoglobinopathy H disease.
Patients with the nondeletion genotype of hemoglobinopathy H (HbH or beta4) disease have higher proportions of HbH and more severe tissue hypoxia than patients with the deletion genotype. Because these patients' red blood cells (RBCs) contain mainly two Hb species, HbH and HbA, the high proportion of HbA can be exploited by lowering its oxygen affinity; this would probably increase oxygen delivery to the RBCs and improve the patients' clinical phenotype. Allosteric effectors that induce a low-affinity Hb may be useful in this regard. We investigated the effect of a bezafibrate derivative, RSR-4, on the oxygen affinity of RBCs and purified hemolysates containing HbA and HbH. This allosteric effector crosses RBC membranes and binds reversibly to the alpha-chains of deoxy-Hb, decreasing hemoglobin oxygen affinity. The blood used was obtained from a patient with HbH disease (alphaTSaudi homozygote) whose HbH level was 33.5% as measured by high-performance liquid chromatography. Oxygen binding studies were performed in RBCs and purified hemolysates. RBCs incubated in the presence of 500 microM RSR-4 (2-[[[(3,5-dichloroanilino)-carbonyl]methyl]phenoxy]-2-methylpropi onic acid) in standard conditions (pH 7.4, 0.14 M NaCl, 37 degrees C) displayed an increase in their P50 value from 14.5 to 35.2 mm Hg. Oxygen binding studies in purified stripped hemolysates (pH 7.2, 0.1 M NaCl, 25 degrees C) showed that addition of both 500 microM RSR-4 and 1 mM of 2,3 diphosphoglycerate (DPG) led to an 11-fold decrease in oxygen affinity, whereas the addition of the natural effector DPG or RSR-4 alone produced a 2.7- and 5.7-fold decrease, respectively. In both cases, the oxygen equilibrium curves (OECs) were biphasic due to the presence of the noncooperative, high-oxygen-affinity HbH (beta4) component. After addition of RSR-4, the lower part of the OEC (corresponding to HbH) was not shifted compared with the upper part (corresponding to HbA). These results were confirmed by kinetic studies of CO recombination. Both experiments demonstrated that RSR-4 does not affect beta4 Hb. Our findings provide an experimental model for lowering the oxygen affinity of HbA in HbH-containing cells and suggest that the oxygen delivery capability of the latter would be thereby improved.
Allosteric Regulation↗
A high incidence of mutations in exon 6 of the low-density lipoprotein receptor gene in Greek familial hypercholesterolemia patients, including a novel mutation.
Explore the source record for details and available documents.
Adolescent↗
Characterization of more than 85% of cystic fibrosis alleles in the Greek population, including five novel mutations.
To completely characterize the spectrum of mutations in the cystic fibrosis transmembrane conductance regulator gene in Greek cystic fibrosis (CF) patients, we screened 500 CF chromosomes by denaturing gradient gel electrophoresis followed by direct sequencing. We identified 48 mutations, accounting for 85.6% of CF chromosomes. They included eight novel mutations, three of which we have described before and five (E822X, Y247X, 2752-26A-->G, 3152delT, and 2751 + T-->A), which are described in this report. The detection of such a high proportion of Greek CF mutations is important for improving prenatal and genetic diagnosis of CF in Greece.
Adult↗
Prenatal diagnosis of the thalassaemia syndromes by rapid DNA analytical methods.
Prenatal diagnostic strategies applied today are based mainly on polymerase chain reaction (PCR) analytical protocols. In Greece a wide range of mutations underlie the thalassaemic haemoglobinopathies, and consequently a variety of PCR-based methods are required to facilitate diagnosis of all potential abnormal genotypes. PCR protocols include those which are relatively simple and others that are technically challenging, but very few have been designed for high through-put clinical diagnostics. Over a period of 18 months we carried out prenatal diagnosis of 147 pregnancies (150 fetal samples) at risk for a wide range of haemoglobinopathies. This involved the precise characterization of parental genotypes and the subsequent analysis of fetal DNA samples. In this series, 18 different mutations in the alpha- or beta-globin clusters were identified. For the characterization of these mutations, five PCR-based protocols were selected: denaturing gradient gel electrophoresis (DGGE), amplification refractory mutation system (ARMS) PCR, restriction endonuclease analysis of PCR fragments, oligonucleotide hybridization and 'gap' PCR for detection of deletions. To avoid spurious diagnosis due to contamination of fetal samples, two additional methods were used to genotype polymorphic variable nucleotide tandem repeat (VNTR) regions of the genome in parental and fetal samples. Through analysis of the results we assess the advantages and drawbacks of the selected PCR-based protocols for providing routine clinical diagnostics.
Alleles↗
The interaction of alpha zero thalassaemia with Hb Icaria: three unusual cases of haemoglobinopathy H.
The clinical, haematological, biosynthetic and molecular data of three Greek haemoglobin H (HbH) disease patients with a distinctive clinical phenotype are described. During infancy all three patients had unusually severe clinical manifestations for HbH disease, with anaemia necessitating blood transfusions, signs of bone changes, growth impairment, and splenomegaly. Molecular analysis identified a rare alpha-thalassaemia genotype (--Med/ alpha Ic alpha). Splenectomy resulted in marked amelioration of the clinical signs; post splenectomy all three patients preserve adequate haemoglobin levels (9-10 g/dl) with growth restored to normal. Despite the initial severe clinical phenotype in these patients, our experience indicates that splenectomy modifies the clinical course to that of mild thalassaemia intermedia. This observation should be considered carefully when giving genetic counselling to families carrying the rare Hb Icaria mutation and an alpha zero thalassaemia mutation.
Autoradiography↗
The triplicated alpha-globin gene locus in beta-thalassaemia heterozygotes: clinical, haematological, biosynthetic and molecular studies.
Excess alpha-globin chains play a major role in the pathophysiology of homozygous beta-thalassaemia. In beta-thalassaemia carriers a minor effect of alpha-globin chain excess is reflected in a minimal or mild anaemia without clinical symptoms. Factors that increase alpha-chain excess in heterozygotes are expected to accentuate the severity of the clinical and haematological phenotype. We report the clinical, haematological, biosynthetic and molecular data in three beta-thalassaemia heterozygotes with the rare interaction of homozygosity for alpha-globin gene triplication, and in 17 heterozygotes with a single additional alpha-globin gene. The three patients homozygous for the alpha-globin gene locus (anti 3.7 kb arrangement) had beta(0)-thalassaemia mutations and a diagnosis of thalassaemia intermedia, preserving haemoglobin levels around 7-8 g/dl. Of the 17 beta-thalassaemia heterozygotes (six children and 11 adults), 16 had severe beta-thalassaemia mutations interacting with an additional alpha-globin gene (13 with alpha alpha alpha anti-3.7 and four with alpha alpha alpha anti-4.2). Compared to simple beta-thalassaemia heterozygotes, they had lower haemoglobin levels and red cell indices, but higher alpha/beta biosynthesis, HbF levels and reticulocytes. Our results suggest that homozygous alpha-gene triplication interacts with a severe beta-thalassaemia mutation to cause an alpha-chain excess equivalent to that observed in homozygous beta-thalassaemia intermedia. In heterozygotes for severe beta-thalassaemia mutations with one additional alpha-globin gene, the alpha-chain excess causes a more pronounced degree of anaemia than is usually seen in simple beta-thalassaemia heterozygotes.
Adult↗
Mutation analysis of ten exons of the CFTR gene in Greek cystic fibrosis patients: characterization of 74.5% of CF alleles including one novel mutation.
To initiate the complete characterization of mutations in the CFTR gene in Greek cystic fibrosis (CF) patients, we screened 184 patients for six relatively common mutations (delta F 508, G542X, G551D, 621 + 1 G-->T, N1303K, W1282X) using allele-specific hybridization and, in addition, analyzed exons 4, 5, 7, 8, 10, 11, 17b, 19, 20 and 21 using the method of denaturing gradient gel electrophoresis (DGGE). Six mutations accounted for 65.9% of the CF alleles in Greek patients, of which the delta F 508 mutation had a frequency of 52.7%. A further 15 previously described mutations accounted for another 8.3% CF alleles and one previously undescribed mutation (3272-4A-->G) was found in one chromosome. The W1282X mutation was not detected at all. Thus, so far, we have identified 21 mutations in the CFTR gene in Greek CF patients, accounting for 74.5% of the CF alleles.
Alleles↗
Identification of two novel mutations (296 + 1G-C and A46D) in exon 2 of the CFTR gene in Greek cystic fibrosis patients.
Two novel CFTR mutations were detected in Greek cystic fibrosis patients. One was a missense mutation, A46D, and the other a splice mutation, 296 + 1G-C. Neither was detected on normal chromosomes.
Adult↗
Mild cystic fibrosis phenotype in patients with the 3272-26A > G mutation.
Explore the source record for details and available documents.
Adolescent↗
Preliminary mutation analysis in the phenylalanine hydroxylase gene in Greek PKU and HPA patients.
The presence of nine mutations in the phenylalanine hydroxylase (PAH) gene, previously described in phenylketonuria (PKU) patients of other Mediterranean and European populations, was assessed in 47 Greek PKU and 3 hyperphenylalaninaemia (HPA) patients. Of the nine mutations investigated, only five were detected, characterizing 31% of the PKU alleles in our patients.
Alleles↗
The molecular basis of normal HbA2 (type 2) beta-thalassemia in Greece.
Heterozygotes for beta-thalassemia usually have raised levels of HbA2, but in Greece about 5% of beta-thalassemia carriers are observed to have normal or borderline levels. It is postulated that such cases have mild beta+ thalassemia mutations or coinheritance of delta-thalassemia. We selected 18 heterozygotes with the hematological phenotype of normal HbA2 (type 2) beta thalassemia who were negative for the delta beta Corfu mutation, and screened them for previously defined Mediterranean beta-thalassemia and delta-thalassemia mutations. The coinheritance of beta and delta-thalassemia was demonstrated in four cases with the following genotypes: in cis beta+ IVSII -n745/delta+ 27, beta 0NS39/delta 059(-A), beta+ IVSI-n110/delta 059(-A) and in trans beta+ IVSI-n6 and delta+ 27. A further nine heterozygotes had mild beta(+)-thalassemia mutations (eight with the beta+ IVSI-n6 mutation, one with the beta+ polyA (A-->G) mutation). In four heterozygotes with severe beta-thalassemia chromosomes (2 beta+ IVSI-n110, 1 beta 0 FSC-6, 1 beta 0 IVSI-n1) no known delta-thalassemia mutations were observed. One case had a delta beta deletion chromosome. These results indicate that the hematological phenotype of normal HbA2 (type 2) beta-thalassemia in Greece is genetically heterogeneous; it is mainly associated with the delta beta Corfu mutation or coinheritance of beta and delta thalassemia mutations or with very mild beta(+)-thalassemia mutations, mainly beta+ IVSI-n6. In the rare cases with severe beta-thalassemia mutations, the normal levels of HbA2 may be due to coinheritance of as yet undefined delta thalassemia mutations.
Base Sequence↗
Characterization of nondeletion alpha-thalassemia mutations in the Greek population.
alpha-Thalassemia is usually due to deletions within the alpha-globin gene cluster, leading to loss of function of one (-alpha) or both [-(alpha) or --] alpha-globin genes. Nondeletion mutations (denoted alpha alpha T or alpha T alpha) are less frequent and in Greece are not well defined. We report the analysis of 16 nondeletion alpha-thalassemia chromosomes using a polymerase chain reaction method to amplify specifically the alpha 2-globin gene, which was subsequently screened using ASO hybridization or restriction enzyme analysis for four mutations already characterized in other Mediterranean and Middle Eastern populations. Of the 16 nondeletion chromosomes, nine had the polyadenylation signal mutation (alpha PolyA alpha), two the IVSI 5' pentanucleotide deletion (alpha Hph alpha), two the Hb Icaria mutation (alpha Ic alpha), and one the initiation codon mutation (alpha Nco alpha). In two, the defects are still undefined. These findings show that nondeletion alpha-thalassemia in Greece is heterogeneous and that the most frequent mutation (accounting for > 50%) is the polyadenylation signal mutation, which to date was most commonly found in the Saudi Arabian population.
Alleles↗
A base substitution (T-->C) in codon 29 of the alpha 2-globin gene causes alpha thalassaemia.
We have identified three individuals of Greek or Greek Cypriot origin with an atypical form of HbH disease characterized by a severe hypochromic microcytic anaemia associated with relatively small amounts of HbH in the peripheral blood. Molecular analysis has shown that each is a compound heterozygote for a previously described mutation affecting the poly A addition signal (AATAAA-->AATAAG) and a previously undescribed mutation involving a T-->C transition in codon 29 of the alpha 2 gene causing a leucine-->proline substitution. Although this mutation would be expected to produce an unstable haemoglobin and hence a haemolytic anaemia, simple heterozygotes for the alpha 29Leu-->Pro mutation have the phenotype of alpha-thalassaemia trait.
Adult↗
A new delta chain variant hemoglobin A2-Corfu or alpha 2 delta 2 116 Arg----Cys (G18), detected by delta-globin gene analysis in a Greek family.
Explore the source record for details and available documents.
Amino Acid Sequence↗
The Corfu delta beta thalassaemia mutation in Greece: haematological phenotype and prevalence.
The Corfu delta beta thalassaemia mutation, a 7.2 kb deletion partially removing the delta-globin gene and a single nucleotide mutation (G----A) at intervening sequence I (IVSI-n5) in the beta-globin gene in cis, was first described in a family from Corfu; the carriers for this mutation had the unusual haematological phenotype of heterozygous beta-thalassaemia with normal levels of HbA2. To investigate the frequency and haematological characteristics of Corfu delta beta thalassaemia in Greece we analysed 25 unrelated normal HbA2 type 2 beta-thalassaemia heterozygotes and their 23 clinically affected offspring. Gene mapping demonstrated that nine (36%) of the 25 normal HbA2 beta-thalassaemia heterozygotes were in fact Corfu delta beta thalassaemia heterozygotes and of the 23 patients, two were Corfu delta beta thalassaemia homozygotes and five compound heterozygotes for Corfu delta beta thalassaemia and another beta-thalassaemia defect. Detailed haematological analysis demonstrated that: the Corfu delta beta thalassaemia mutation does not completely abolish the expression of the beta-globin gene; the HbA2 levels are slightly lower (P less than 0.01) and the HbF levels slightly higher (P less than 0.01) in Corfu delta beta thalassaemia heterozygotes compared to beta-thalassaemia heterozygotes with the normal HbA2-type 2 phenotype who do not have the Corfu delta beta chromosome.
Chromosome Deletion↗
Correlation of clinical phenotype to genotype in haemoglobin H disease.
Clinical assessment, haematological studies, and globin gene mapping were performed in 21 Greek subjects with haemoglobin H disease. Clinical phenotypes ranged from mild, and virtually asymptomatic, to severe cases requiring transfusion. The severe clinical phenotype was exclusively associated with non-deletion genotypes, whereas the mild and intermediate phenotypes occurred with deletion genotypes. Patients with non-deletion genotypes had higher levels of Hb H. For deletion genotypes of haemoglobin H disease, the value of antenatal diagnosis is questionable. In non-deletion genotypes, antenatal diagnosis should be considered, because of the more severe clinical course observed in these patients.
Adolescent↗