Genetic modifiers of beta-thalassemia.
TL;DR: The clinical and hematologic diversity encountered in beta thalassemia is reviewed with an overview of the modifier genes that moderate their disease expression.
Abstract: As the defective genes for more and more genetic disorders become unravelled, it is clear that patients with apparently identical genotypes can have many different clinical conditions even in simple monogenic disorders. Beta thalassemia occurs when there is a deficiency in the synthesis of beta globin chains. The clinical manifestations of beta thalassemia are extremely diverse, spanning a broad spectrum from severe anemia and transfusion-dependency to the asymptomatic state of thalassemia trait. The remarkable phenotypic diversity of the beta thalassemias is prototypical of how a wide spectrum of disease severity can be generated in single gene disorders. The most reliable and predictive factor of disease phenotype is the nature of the mutation at the beta globin locus itself. However, relating phenotype to genotype is complicated by the complex interaction of the environment and other genetic factors at the secondary and tertiary levels, some implicated from family studies, and others, as yet unidentified. This article reviews the clinical and hematologic diversity encountered in beta thalassemia with an overview of the modifier genes that moderate their disease expression.
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TL;DR: More than 100 varieties of α-thalassemia have been identified and their geographic distribution and the challenges associated with screening, diagnosis, and management suggest they should have a higher priority on global public health agendas.
Abstract: More than 100 varieties of α-thalassemia have been identified. Their geographic distribution and the challenges associated with screening, diagnosis, and management suggest that α-thalassemias should have a higher priority on global public health agendas.
333 citations
TL;DR: It is revealed that all the three reported loci and the α-globin gene locus are the best and common predictors of the disease severity in β-thalassemia.
Abstract: β-Thalassemia/HbE disease is clinically variable. In searching for genetic factors modifying the disease severity, patients were selected based on their disease severities, and a genome-wide association study (GWAS) was performed. Genotyping was conducted with the Illumina Human 610-Quad BeadChips array using DNAs from 618 Thai β0-thalassemia/HbE patients who were classified as 383 severe and 235 mild phenotypes by a validated scoring system. Twenty-three SNPs in three independent genes/regions were identified as being significantly associated with the disease severity. The highest association was observed with SNPs in the β-globin gene cluster (chr.11p15), and rs2071348 of the HBBP1 gene revealed the most significant association [P = 2.96 × 10−13, odds ratio (OR) = 4.33 (95% confidence interval (CI), 2.74–6.84)]. The second was identified in the intergenic region between the HBS1L and MYB genes (chr.6q23), among which rs9376092 was the most significant [P = 2.36 × 10−10, OR = 3.07 (95% CI, 2.16–4.38)]. The third region was located in the BCL11A gene (chr.2p16.1), and rs766432 showed the most significant association [P = 5.87 × 10−10, OR = 3.06 (95% CI, 2.15–4.37)]. All three loci were replicated in an independent cohort of 174 Indonesian patients. The associations to fetal hemoglobin levels were also observed with SNPs on these three regions. Our data indicate that several genetic loci act in concert to influence HbF levels of β0-thalassemia/HbE patients. This study revealed that all the three reported loci and the α-globin gene locus are the best and common predictors of the disease severity in β-thalassemia.
174 citations
Cites background from "Genetic modifiers of beta-thalassem..."
...In addition, multiple modifying factors in several pathways involved in the pathophysiology of the disease have been identified (Thein 2005)....
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29 Feb 2012
TL;DR: The complex and heterogeneous spectrum of molecular defects underlying these inherited conditions is regionally specific and in most cases the geographic and ethnic distributions have been determined, providing support for prevention programs based on screening, genetic counselling and prenatal diagnosis in couples at risk.
Abstract: Hemoglobinopathies are a heterogeneous group of monogenic disorders widespread overall. They are commonly subdivided into three partially overlapping subgroups: structural variants which comprise the sickle cell anemia syndrome; thalassemias, characterized by a reduced rate of synthesis of one or more globin chains of hemoglobin; conditions of high persistence of fetal hemoglobin in adulthood (HPFH) (Weatherall & Clegg, 2001). As a group, they are the commonest monogenic disorders in the world population. It is thought that the high prevalence of these defects could be due to selective advantage of the carrier state to malaria infection. However, in spite of epidemiological evidences supporting this hypothesis as well as of extensive hematological studies, the mechanisms underlying this protection still remain unknown. It is, however, evident that as a consequence of this positive selection, these diseases are mostly common in geographic areas extending from the Mediterranean region through tropical countries including Sub-Saharian Africa, the Middle East, India, Southeast Asia and Indonesia, where malaria was or still is endemic (Weatherall & Clegg, 2001). In many of these areas the estimated frequencies of these disorders range from 3 to 10 percent, even though in some specific areas the carrier frequencies may be higher, reaching 80-90% in some tribal populations in India (Harteveld & Higgs, 2010). Because of their high frequencies, different hemoglobin defects may be co-inherited, giving rise to an extremely complex series of genotypes and clinical phenotypes. In fact, in many regions thalassemic defects coexist with structural Hb variants; it is also quite common for individuals from areas at high frequency of thalassemic defects to inherit genes for more than one type of thalassemia. Furthermore, some Hb variants are synthesized at reduced rate or are highly instable, leading both to functional and structural deficiency of the affected globin chain, thus resulting in a thalassemic condition, generally showing dominant inheritance. These complex interactions contribute to generate a wide range of clinical disorders that, taken together, constitute the thalassemic syndromes (Weatherall, 2001). The complex and heterogeneous spectrum of molecular defects underlying these inherited conditions is regionally specific and in most cases the geographic and ethnic distributions have been determined, providing support for prevention programs based on screening, genetic counselling and prenatal diagnosis in couples at risk.
155 citations
Cites background from "Genetic modifiers of beta-thalassem..."
...…-globin genes may produce a more marked imbalance in globin chain production thus leading to a clinical picture of thalassemia intermedia even in simple heterozygotes for -thalassemia, who are otherwise generally clinically silent (Cao & Moi, 2002; Thein, 2005; Weatherall, 2001; Wong et al., 2004)....
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...On the other hand, triplication or quadruplication rearrangements of -globin genes may produce a more marked imbalance in globin chain production thus leading to a clinical picture of thalassemia intermedia even in simple heterozygotes for -thalassemia, who are otherwise generally clinically silent (Cao & Moi, 2002; Thein, 2005; Weatherall, 2001; Wong et al., 2004)....
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TL;DR: Comments on the need for accuracy and standardisation are included and a practical flow-chart is presented to summarise the significance of HbA2 estimation in different thalassaemia syndromes and related haemoglobinopathies.
Abstract: The increase in haemoglobin (Hb)A(2) level is the most significant parameter in the identification of beta thalassaemia carriers. However, in some cases the level of HbA(2) is not typically elevated and some difficulties may arise in making the diagnosis. For these reasons the quantification of HbA(2) has to be performed with great accuracy and the results must be interpreted together with other haematological and biochemical evidence. The present document includes comments on the need for accuracy and standardisation, and on the interpretation of the HbA(2) value, reviewing the most crucial aspects related to this test. A practical flow-chart is presented to summarise the significance of HbA(2) estimation in different thalassaemia syndromes and related haemoglobinopathies.
154 citations
TL;DR: IthaGenes is a new interactive database of haemoglobin variations, which stores information about genes and variations affecting ha Hemoglobin disorders, while embedding the NCBI Sequence Viewer for graphical representation of each variation.
Abstract: Inherited haemoglobinopathies are the most common monogenic diseases, with millions of carriers and patients worldwide. At present, we know several hundred disease-causing mutations on the globin gene clusters, in addition to numerous clinically important trans-acting disease modifiers encoded elsewhere and a multitude of polymorphisms with relevance for advanced diagnostic approaches. Moreover, new disease-linked variations are discovered every year that are not included in traditional and often functionally limited locus-specific databases. This paper presents IthaGenes, a new interactive database of haemoglobin variations, which stores information about genes and variations affecting haemoglobin disorders. In addition, IthaGenes organises phenotype, relevant publications and external links, while embedding the NCBI Sequence Viewer for graphical representation of each variation. Finally, IthaGenes is integrated with the companion tool IthaMaps for the display of corresponding epidemiological data on distribution maps. IthaGenes is incorporated in the ITHANET community portal and is free and publicly available at http://www.ithanet.eu/db/ithagenes.
151 citations
Cites background from "Genetic modifiers of beta-thalassem..."
...However, demographic events, such as migration and the consequent intermixing of populations, have contributed to the spread of Hb disorders worldwide [3,4]....
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References
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TL;DR: The study of iron biology has provided novel insights into gene regulation and unveiled remarkable links to the immune system.
1,687 citations
TL;DR: The lesser genetic contribution to proximal femur and distal forearm bone mass compared with the spine suggests that environmental factors are of greater importance in the aetiology of osteopenia of the hip and wrist.
Abstract: The relative importance of genetic factors in determining bone mass in different parts of the skeleton is poorly understood. Lumbar spine and proximal femur bone mineral density and forearm bone mineral content were measured by photon absorptiometry in 38 monozygotic and 27 dizygotic twin pairs. Bone mineral density was significantly more highly correlated in monozygotic than in dizygotic twins for the spine and proximal femur and in the forearm of premenopausal twin pairs, which is consistent with significant genetic contributions to bone mass at all these sites. The lesser genetic contribution to proximal femur and distal forearm bone mass compared with the spine suggests that environmental factors are of greater importance in the aetiology of osteopenia of the hip and wrist. This is the first demonstration of a genetic contribution to bone mass of the spine and proximal femur in adults and confirms similar findings of the forearm. Furthermore, bivariate analysis suggested that a single gene or set of genes determines bone mass at all sites.
1,270 citations
TL;DR: Pulmonary hypertension appears to be a complication of chronic hemolysis, is resistant to hydroxyurea therapy, and confers a high risk of death in adults with sickle cell disease.
Abstract: Background The prevalence of pulmonary hypertension in adults with sickle cell disease, the mechanism of its development, and its prospective prognostic significance are unknown. Methods We performed Doppler echocardiographic assessments of pulmonary-artery systolic pressure in 195 consecutive patients (82 men and 113 women; mean [±SD] age, 36±12 years). Pulmonary hypertension was prospectively defined as a tricuspid regurgitant jet velocity of at least 2.5 m per second. Patients were followed for a mean of 18 months, and data were censored at the time of death or loss to follow-up. Results Doppler-defined pulmonary hypertension occurred in 32 percent of patients. Multiple logistic-regression analysis, with the use of the dichotomous variable of a tricuspid regurgitant jet velocity of less than 2.5 m per second or 2.5 m per second or more, identified a self-reported history of cardiovascular or renal complications, increased systolic blood pressure, high lactate dehydrogenase levels (a marker of hemolysis...
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TL;DR: The distribution of the C282Y mutation coincides with that of populations in which haemochromatosis has been reported and is consistent with the theory of a north European origin for the mutation.
Abstract: Haemochromatosis is a genetic disease associated with progressive iron overload, and is common among populations of northern European origin HLA-H is a recently reported candidate gene for this condition Two mutations have been identified, a substitution of cysteine for tyrosine at amino acid 282 (C282Y, nucleotide 845) and of histidine for aspartate at amino acid 63 (H63D, nucleotide 187) Over 90% of UK haemochromatosis patients are homozygous for the C282Y mutation We have examined 5956 chromosomes (2978 people) for the presence of HLA-H C282Y and H63D by PCR followed by restriction enzyme analysis We have found world wide allele frequencies of 19% for C282Y and 81% for H63D The highest frequencies were 10% for C282Y in 90 Irish chromosomes and 304% for H63D in 56 Basque chromosomes C282Y was most frequent in northern European populations and absent from 1042 African chromosomes, 484 Asian chromosomes, and 644 Australasian chromosomes The distribution of the C282Y mutation coincides with that of populations in which haemochromatosis has been reported and is consistent with the theory of a north European origin for the mutation The H63D polymorphism is more widely distributed and its connection with haemochromatosis remains unclear
758 citations
TL;DR: The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKlF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.
Abstract: We describe a novel erythroid cell-specific cDNA (EKLF [erythroid Kruppel-like factor]) isolated by enriching for genes expressed in a mouse erythroleukemia cell line but not expressed in a mouse monocyte-macrophage cell line. The complete cDNA sequence is predicted to encode a protein of approximately 38,000 Da that contains a proline-rich amino domain and three TFIIIA-like zinc fingers within the carboxy domain. Additional sequence analyses reveal that the EKLF zinc fingers are most homologous to the Kruppel family of transcription factors and also allow us to predict potential DNA-binding target sites for the EKLF protein. On the basis of this prediction, we show that EKLF is able to bind the sequence CCA CAC CCT, an essential element of the beta-globin promoter. Its tissue distribution establishes that the EKLF transcript is expressed only in bone marrow and spleen, the two hematopoietic organs of the mouse, and analysis of murine cell lines indicates that EKLF expression is limited to erythroid and mast cell lines. Cotransfection assays establish that EKLF transcriptionally activates a target promoter that contains its DNA-binding site. The tissue expression pattern of EKLF, in conjunction with its function as a transcriptional activator, strongly suggests that the EKLF protein may be intimately involved in establishment and/or maintenance of the erythroid cell phenotype.
749 citations