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

The regulation of human globin promoters by CCAAT box elements and the recruitment of NF-Y

CCAAT boxes are motifs found within the proximal promoter of many genes, including the human globin genes. The highly conserved nature of CCAAT box motifs within the promoter region of both α-like and β-like globin genes emphasises the functional importance of the CCAAT sequence in globin gene regulation. Mutations within the β-globin CCAAT box result in β-thalassaemia, while mutations within the distal γ-globin CCAAT box cause the Hereditary Persistence of Foetal Haemoglobin, a benign condition which results in continued γ-globin expression during adult life. Understanding the transcriptional regulation of the globin genes is of particular interest, as reactivating the foetal γ-globin gene alleviates the symptoms of β-thalassaemia and sickle cell anaemia. NF-Y is considered to be the primary activating transcription factor which binds to globin CCAAT box motifs. Here we review recruitment of NF-Y to globin CCAAT boxes and the role NF-Y plays in regulating globin gene expression. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Two new β+ -thalassemia mutation [β -56 (G → C); HBBc. -106 G → C] and [β -83 (G → A); HBBc. -133 G → A] described among the Tunisian population

OBJECTIVES

Different thalassemia mutations have been reported in various ethnic groups and geographical regions in Tunisia. In the present study, we have investigated two rare β(+) -thalassemia mutations, that have not previously been reported in the Tunisian population [β -56 (G > C); HBBc. -106 G > C] and [β -83 (G > A); HBBc. -133 G > A].

METHODS

The whole β-globin gene was directly sequenced, and haplotype analysis was conducted through a PCR/RFLP method.

RESULTS

Two new mutations were identified for the first time in Tunisia. They are located within the promoter region of β-globin gene at position -56 (G > C) and -83 (G > A). Linkage analysis using β-globin gene cluster haplotypes showed that these two mutations were associated with Mediterranean β-haplotype IX [- + - + + + +] and framework 2 (FW2) [CCTCT].

CONCLUSIONS

The two newly described mutations lead to the β(+) -thalassemia among Tunisian patients. The haplotype analysis and framework assignment have helped to identify the chromosomal background associated with these mutations, and determine their origin and spread.

The significance of the hemoglobin A(2) value in screening for hemoglobinopathies

BACKGROUND AND OBJECTIVE

The inherited hemoglobinopathies are a large group of disorders that include thalassemias and hemoglobin variants. Accurate determination of the carrier phenotype is essential for detecting couples at risk for producing offspring with hemoglobinopathy. Heterozygous beta-thalassemia is usually silent at the clinical level. His phenotype is characterized by microcytosis and hypochromia with increased hemoglobin A(2) (HbA(2)) value. Therefore, HbA(2) determination plays a key role in screening programs for hemoglobinopathy. The aim of this review is to address and suggest an approach for reducing or abolishing hemoglobinopathy screening mistakes.

DESIGN AND METHODS

Quantitative methods for HbA(2) value determination, comment on the accuracy of the test and on the interpretation of data were discussed. The most probable diagnostic conclusion based on the HbA(2) level, hemoglobin pattern, hematological parameters and iron markers was suggested in this review.

RESULTS

Hemoglobinopathies are the only genetic disease where it is possible to detect carriers using hematological findings rather than DNA analysis. However, hematological diagnosis is sometimes presumptive, and in these cases, DNA analysis becomes necessary. Complete screening is based on the detection of red cell indices, HbA(2), HbF and hemoglobin variant values. In particular, HbA(2) determination plays a key role in screening programs for beta-thalassemia because a small increase in this fraction is one of the most important markers of beta-thalassemia heterozygous carriers.

CONCLUSION

Genetic factors both related and unrelated to the beta- and alpha-globin gene clusters, iron metabolism, endocrinological disorders, and some types of anemia, together with intra- and inter-laboratory variations in HbA(2) determination, may cause difficulties in evaluating this measurement in screening programs for hemoglobinopathies. Therefore, knowledge of all these issues is important for reducing or eliminating the risk of mistakes in screening programs for hemoglobinopathies.

HbS/beta(del)-thalassemia associated with high levels of hemoglobins A2 and F in a Turkish family

Beta-thalassemia and sickle cell disease (SCD) are common disorders in Turkey. Compound heterozygosity for these two disorders (betaS/beta-thalassemia) is encountered frequently. In this report we present hematological and molecular data of two Turkish siblings with betaS/beta(del)-thalassemia caused by a 290 base pair (bp) deletion and associated with increased levels of hemoglobin A2 (HbA2) and hemoglobin F (HbF). Clinical analysis of the two patients showed a mild course of the disease. Haplotypic factors involved in increasing the levels of HbF were analyzed. The two patients showed no changes from the normal sequences at the XmnI site of Ggamma-globin promoter and the (AT)xTy microsatellite 5' to the beta-globin mRNA cap site. The removal of the region between positions -125 to +78 relative to the beta-globin gene mRNA cap site by the 290 bp deletion is thought to allow the beta-locus control region to interact with the promoters of the delta- and gamma-globin genes, leading to increased HbA2 and HbF levels.

Absence of mutations in the promoter of the COL1A1 gene of type I collagen in patients with osteogenesis imperfecta type I

Osteogenesis imperfecta type I results from decreased production of structurally normal type I collagen as a result of a COL1A1 "null" allele. Steady state amounts of COL1A1 mRNA are reduced in both the nucleus and cytoplasm of dermal fibroblasts from most affected subjects. Mutations involving key regulatory sequences in the COL1A1 promoter, such as the TATAAA and CCAAAT boxes, could alter steady state levels of mRNA, and therefore lead to this phenotype. To determine the frequency of such mutations in OI type I cell strains, we used PCR amplified genomic DNA in conjunction with denaturing gradient gel electrophoresis (DGGE) and SSCP, to screen the 5' untranslated domain, exon 1, and a small portion of intron 1 of the COL1A1 gene. In addition, direct sequence analysis was performed on an amplified genomic DNA fragment that included the TATAAA and CCAAAT boxes. Forty unrelated probands with OI type I, in whom no causative mutation was known, were included in the study. No mutations were included in the study. No mutations were identified in either the TATAAA or CCAAAT boxes in any of the affected people. In addition, there was little evidence of sequence diversity among any of the 40 subjects. These data suggest that mutations in the COL1A1 promoter do not play a significant role in the aetiology of OI type I.

A promoter mutation, C-->T at position -92, leading to silent beta-thalassaemia

This study describes the clinical phenotype of the C-->T mutation at position -92 of the beta-globin gene. Excluding two cases with HbA2 levels within the range of the beta-thalassemia carrier state, heterozygotes for this mutation showed normal or borderline red blood cells count, Hb levels, MCV, MCH and HbA2 values, and unbalanced globin chain synthesis. Compound heterozygotes for the -92 C-->T mutation and a beta zero-thalassaemia mutation (beta zero 39) (two cases) or severe beta+-thalassaemia (beta+ IVSII nt 745) (two cases) developed thalassaemia intermedia. According to these characteristics, the -92 promoter mutation should be added to the list of silent beta-thalassaemias.

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.