Variability of hemoglobin F expression in hemoglobin EE disease: hematological and molecular analysis.
TL;DR: Examining multiple single nucleotide polymorphisms in the β-globin gene cluster, BCL11A and HBS1L-MYB genes determined their associations with Hb F levels in Hb E disorder and demonstrated that multiple genetic modifying factors including T allele of (G)γ-XmnI polymorphism, G allele of HBS 1L- MYB, and C allele of BCL 11A are associated with increased HbF.
Abstract: Although the molecular basis of variability of hemoglobin (Hb) F has been extensively examined in β-thalassemia and sickle cell diseases, less study has been done on Hb E disorder. To address the variability of Hb F expression in Hb EE disease, we have examined multiple single nucleotide polymorphisms (SNPs) in the β-globin gene cluster, BCL11A and HBS1L-MYB genes and determined their associations with Hb F levels in this syndrome. Study was done on 141 adult Thai individuals with homozygous Hb E. Hematological parameters were recorded and Hb F measured using Hb-HPLC analyzer. It was found in 26 cases that co-inheritance of α-thalassemia could lead to significant lower production of Hb F. Association of Hb F expression with the Gγ-Xmn I polymorphism and other SNPs including rs2297339, rs2838513, rs4895441 and rs9399137 in HBS1L-MYB gene and rs4671393 and rs11886868 in BCL11A gene was therefore analyzed in the remaining 115 cases without α-thalassemia. It was found that 4 of these 7 SNPs including Gγ-XmnI polymorphism (rs7482144), HBS1L-MYB (rs4895441) and (rs9399137) and BCL11A (rs4671393) were significantly associated with higher proportions of subjects with high Hb F (Hb F ≥ 5%). The result demonstrated that multiple genetic modifying factors including T allele of Gγ-XmnI polymorphism (rs7482144), G allele of HBS1L-MYB (rs489441), C allele of HBS1L-MYB (rs9399137) and C allele of BCL11A (rs4671393) are associated with increased Hb F and in combination could explain approximately 80% of the variation of Hb F in Hb EE disease in Thai population. Other genetic factors regulating Hb F expression in this common genetic disorder remains to be elucidated.
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TL;DR: The XmnI locus, rs11886868, and rs766432 have a modifying effect on HbF and clinical score in HbE/β-thal patients in Indonesia, but not in β-thal Patients.
37 citations
Cites result from "Variability of hemoglobin F express..."
...The distribution of rs11886868 genotype in this study has a similar frequency with the populations of China and Thailand, as reported by Pakdee and colleagues [35]....
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TL;DR: This article will review the heterogeneity and genetic modifiers of HfF and HbF induction therapy in β-thalassemia and suggest further understanding of Hbf level variation and regulation is needed in order to predict the response from H bF-inducing approaches.
Abstract: Introduction: Stress erythropoiesis induces fetal hemoglobin (HbF) expression in β-thalassemias, however the level of expression is highly variable. The last decade has seen dramatic advances in our understanding of the molecular regulators of HbF production and the genetic factors associated with HbF levels, leading to the promise of new methods of the clinical induction of HbF.Areas covered: This article will review the heterogeneity and genetic modifiers of HbF and HbF induction therapy in β-thalassemia.Expert commentary: One promising curative β-thalassemia therapy is to induce HbF synthesis in β-thalassemic erythrocytes to therapeutic levels before clinical symptom occurs. Further understanding of HbF level variation and regulation is needed in order to predict the response from HbF-inducing approaches.
33 citations
Cites background from "Variability of hemoglobin F express..."
...6 [18] Homozygous HbE 1–8 [18,23] Homozygous β-thalassemia 95–98 [14] Homozygous β-thalassemia 70–90 [14] Compound heterozygous β/β-thalassemia 70–90 [14] β-thalassemia/HbE 2–76 [17,24] Mildly affected 42....
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...between 1% and 8%, with a mean of 4% [23]....
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...zygote [51], HbE heterozygote [51], and HbE homozygote [23]....
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TL;DR: Most of the β(+)-thalassemia carriers had elevated Hb A2 and mild hypochromic microcytosis, some demonstrated borderline MCV and MCH values which, could compromise carrier screening.
Abstract: We report the molecular and hematological characteristics associated with a large cohort of β(+)-thalassemia in Thailand. Study was done on 21,068 unrelated subjects referred to our center in northeast Thailand for hemoglobinopathies investigation. Among 21,068 subjects, 2637 (12.5%) were found to carry β-thalassemia. Of these 2637 cases, 705 (26.7%) carried β(+)-thalassemia with eight different mutations including 6 promoter mutations; NT-28 (A-G), NT-31 (A-G), NT-50 (G-A), NT-86 (C-G), NT-87 (C-A) and NT-90 (C-T) and two missense mutations; Hb Malay (codon 19; AAC-AGC) and Hb Dhonburi (codon 126; GTG-GGG). Hematological features of carriers with these β(+)-thalassemia (n=528) were compared with those with β(0)-thalassemia (n=309). Data for Hb E-β(+)-thalassemia (n=177) were also presented along with Hb E-β(0)-thalassemia in our series (n=94). All patients with Hb E-β(+)-thalassemia were associated with mild thalassemia intermedia phenotypes. Most of the β(+)-thalassemia carriers had elevated Hb A2 and mild hypochromic microcytosis, some demonstrated borderline MCV and MCH values which, could compromise carrier screening. Analysis of α/β-globin mRNA ratio in representative cases with normal, Hb E trait, β(+)-thalassemia trait, Hb Dhonburi trait and β(0)-thalassemia trait demonstrated the average values of 1.1, 1.7, 2.1, 1.7 and 3.1, respectively which is helpful in identification and differentiation of the cases.
27 citations
TL;DR: Results indicate that KLF1 is among the genetic factors associated with increased Hbs F and A2, and in combination with other factors could explain the variabilities of these Hb expression in Hb E syndrome.
Abstract: The basis for variability of hemoglobin (Hb) F in homozygous Hb E disease is not well understood. We have examined multiple mutations of the Kruppel-like factor 1 (KLF1) gene; an erythroid specific transcription factor and determined their associations with Hbs F and A2 expression in homozygous Hb E. Four KLF1 mutations including G176AfsX179, T334R, R238H, and −154 (C-T) were screened using specific PCR assays on 461 subjects with homozygous Hb E and 100 normal controls. None of these four mutations were observed in 100 normal controls. Among 461 subjects with homozygous Hb E, 306 had high (≥5 %) and 155 had low (<5 %) Hb F. DNA analysis identified the KLF1 mutations in 35 cases of the former group with high Hb F, including the G176AfsX179 mutation (17/306 = 5.6 %), T334R mutation (9/306 = 2.9 %), −154 (C-T) mutation (7/306 = 2.3 %), and R328H mutation (2/306 = 0.7 %). Only two subjects in the latter group with low Hb F carried the G176AfsX179 and −154 (C-T) mutations. Significant higher Hb A2 level was observed in those of homozygous Hb E with the G176AfsX179 mutation as compared to those without KLF1 mutations. These results indicate that KLF1 is among the genetic factors associated with increased Hbs F and A2, and in combination with other factors could explain the variabilities of these Hb expression in Hb E syndrome.
19 citations
TL;DR: Combined KLF1 mutations with other SNPs including (G)γ-XmnI, BCL11A and HBS1L-MYB were associated with higher Hb F levels, and KLF 1 is therefore an important genetic factor associated with increased HB F and in combination with other modifying factors could explain the phenotypic variation of H b F expression in this common hemoglobinopathy.
Abstract: Hemoglobin E is the most common Hb variant found in South East Asia. Variation of Hb F expression in Hb E syndrome is associated with several genetic modifiers. We report several single nucleotide polymorphisms (SNPs), including nine known and five novel mutations of the Kruppel-like factor 1 (KLF1; an erythroid specific transcription factor) gene and determine their associations with phenotypic expression of Hb F in Hb E disorders. KLF1 mutations were examined using high resolution melting (HRM) assay and DNA sequencing in 575 homozygous Hb E, 278 heterozygous Hb E and 100 normal subjects. Fourteen mutations were mostly observed in subjects with elevated Hb F, including nine known mutations (G176AfsX179, T334R, R238H, -154 (C>T), A298P, S270W, R301H, -148 (G>A) and G335R and five novel mutations (Q217X, Q223X, Y290_S293del, K307N, and M358I). None of them, but the -148 (G>A), were observed in normal controls to have Hb F <1%. Combined KLF1 mutations with other SNPs including (G)γ-XmnI, BCL11A and HBS1L-MYB were associated with higher Hb F levels. KLF1 is therefore an important genetic factor associated with increased Hb F and in combination with other modifying factors could explain the phenotypic variation of Hb F expression in this common hemoglobinopathy.
15 citations
Cites background from "Variability of hemoglobin F express..."
...These include a T allele of the γ XmnI (rs7482144), A allele of the BCL11A (rs4671393), G allele of the HBS1L-MYB (rs4895441) and C allele of the HBS1L-MYB (rs9399137) [15]....
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...We further examined the combined effect of KLF1 mutations and other SNPs, including γ XmnI (rs7482144), BCL11A (rs4671393) and HBS1L-MYB (rs4895441) & (rs9399137) known to be involved in Hb F expression in our population [9,15]....
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...the γ-XmnI (rs7482144), BCL11A (rs4671393), HBS1L-MYB (rs4895441) and (rs9399137) [15] are also presented....
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References
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TL;DR: BCL11A emerges as a therapeutic target for reactivation of HbF in β-hemoglobin disorders and occupies several discrete sites in the β-globin gene cluster, consistent with a direct role of BCL 11A in globin gene regulation.
Abstract: Differences in the amount of fetal hemoglobin (HbF) that persists into adulthood affect the severity of sickle cell disease and the beta-thalassemia syndromes. Genetic association studies have identified sequence variants in the gene BCL11A that influence HbF levels. Here, we examine BCL11A as a potential regulator of HbF expression. The high-HbF BCL11A genotype is associated with reduced BCL11A expression. Moreover, abundant expression of full-length forms of BCL11A is developmentally restricted to adult erythroid cells. Down-regulation of BCL11A expression in primary adult erythroid cells leads to robust HbF expression. Consistent with a direct role of BCL11A in globin gene regulation, we find that BCL11A occupies several discrete sites in the beta-globin gene cluster. BCL11A emerges as a therapeutic target for reactivation of HbF in beta-hemoglobin disorders.
794 citations
TL;DR: Genotyping additional BCL11A SNPs, HBS1L-MYB SNPs and an SNP upstream of Gγ-globin (HBG2; the XmnI polymorphism) provided a clear example of inherited common sequence variants modifying the severity of a monogenic disease.
Abstract: Sickle cell disease (SCD) is a debilitating monogenic blood disorder with a highly variable phenotype characterized by severe pain crises, acute clinical events, and early mortality. Interindividual variation in fetal hemoglobin (HbF) expression is a known and potentially heritable modifier of SCD severity. High HbF levels are correlated with reduced morbidity and mortality. Common single nucleotide polymorphisms (SNPs) at the BCL11A and HBS1L-MYB loci have been implicated previously in HbF level variation in nonanemic European populations. We recently demonstrated an association between a BCL11A SNP and HbF levels in one SCD cohort [Uda M, et al. (2008) Proc Natl Acad Sci USA 105:1620-1625]. Here, we genotyped additional BCL11A SNPs, HBS1L-MYB SNPs, and an SNP upstream of (G)gamma-globin (HBG2; the XmnI polymorphism), in two independent SCD cohorts: the African American Cooperative Study of Sickle Cell Disease (CSSCD) and an SCD cohort from Brazil. We studied the effect of these SNPs on HbF levels and on a measure of SCD-related morbidity (pain crisis rate). We strongly replicated the association between these SNPs and HbF level variation (in the CSSCD, P values range from 0.04 to 2 x 10(-42)). Together, common SNPs at the BCL11A, HBS1L-MYB, and beta-globin (HBB) loci account for >20% of the variation in HbF levels in SCD patients. We also have shown that HbF-associated SNPs associate with pain crisis rate in SCD patients. These results provide a clear example of inherited common sequence variants modifying the severity of a monogenic disease.
537 citations
TL;DR: Cet article etudie successivement la frequence de la thalassemie β, des variants genetiques de la chaine α et de the chaine β, de l'hemoglobine constant spring et oficiairement l'HbE.
Abstract: Cet article etudie successivement la frequence de la thalassemie α, de la thalassemie β, des variants genetiques de la chaine α et de la chaine β, de l'hemoglobine constant spring et de l'HbE
298 citations
"Variability of hemoglobin F express..." refers background in this paper
...Hemoglobin (Hb) E is the most common β-globin chain variant (α2β2) in Southeast Asian populations [1]....
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TL;DR: A classical twin study in unselected twins demonstrated that the variance of FC levels in healthy adults is largely genetically determined.
284 citations
TL;DR: It is reported here that the complete nucleotide sequence of a βE-gene revealed the expected GAG → AAG change in codon 26 but no other mutations, demonstrating a disturbance in the expression of the βE -gene attributable solely to the exon mutation—a novel mechanism for gene dysfunction.
Abstract: As is typical of all beta-thalassaemias, the erythroid cells of individuals with the variant haemoglobin E (alpha 2 beta 2(26Glu leads to Lys)) exhibit a quantitative deficiency in their content of beta-globin (in this case beta E-globin) and its messenger RNA2,3. To determine the molecular basis of this phenotype, we have investigated the structure and expression of cloned beta E-globin genes. We report here that the complete nucleotide sequence of a beta E-gene revealed the expected GAG leads to AAG change in codon 26 but no other mutations. Expression of beta E-globin genes introduced into HeLa cells revealed two abnormalities of RNA processing: slow excision of intervening sequence-1 (IVS-1) and alternative splicing into exon-1 at a cryptic donor sequence within which the codon 26 nucleotide substitution resides. These results demonstrate a disturbance in the expression of the beta E-gene attributable solely to the exon mutation-a novel mechanism for gene dysfunction.
279 citations