Étude de la collaboration entre les facteurs de transcription hématopoïétiques lors du développement et de la différenciation des cellules érythroïdes

La régulation transcriptionnelle des gènes est cruciale pour permettre le bon fonctionnement des cellules. Afin que les cellules puissent accomplir leurs fonctions, les gènes doivent être exprimés adéquatement dans le bon type cellulaire et au stade de développement et de différenciation approprié. Un dérèglement dans l’expression de un ou plusieurs gènes peut entraîner de graves conséquences sur le destin de la cellule. Divers éléments en cis (ex : promoteurs et enhancers) et en trans (machinerie transcriptionnelle et facteurs de transcription) sont impliqués dans la régulation de la transcription. Les gènes du locus humain beta-globine (hub) sont exprimés dans les cellules érythroïdes et sont finenement régulés lors du développement et de la différenciation. Des mutations dans différentes régions du locus causent entre autres les beta-thalassémies. Nous avons utilisé ce modèle bien caractérisé afin d’étudier différents mécanismes de régulation favorisés par les facteurs de transcription qui sont exprimés dans les cellules érythroïdes. Nous nous sommes intéressés à l’importance de l’élément en cis HS2 du Locus control region. Cet élément possède plusieurs sites de liaison pour des facteurs de transcription impliqués dans la régulation des gènes du locus hub. Nos résultats montrent que HS2 possède un rôle dans l’organisation de la chromatine du locus qui peut être dissocié de son rôle d’enhancer. De plus, HS2 n’est pas essentiel pour l’expression à haut niveau du gène beta alors qu’il est important pour l’expression des gènes gamma. Ceci suggère que le recrutement des différents facteurs au site HS2 lors du développement influence différement les gènes du locus. Dans un deuxième temps, nous avons investigué l’importance de HS2 lors de la différenciation des cellules érythroïdes. Il avait été rapporté que l’absence de HS2 influence grandement la potentialisation de la chromatine du gène beta. La potentialisation dans les cellules progénitrices favorise l’activation transcriptionnelle du gène dans les cellules matures. Nous avons caractérisé le recrutement de différents facteurs de transcription au site HS2 et au promoteur beta dans les cellules progénitrices hématopoïétiques (CPH) ainsi que dans les cellules érythroïdes matures. Nos résultats montrent que le facteur EKLF est impliqué dans la potentialisation de la chromatine et favorise le recrutement des facteurs BRG1, p45 et CBP dans les CPH. L’expression de GATA-1 dans les cellules érythroïdes matures permet le recrutement de GATA-1 au locus hub dans ces cellules. Ces données suggèrent que la combinaison de EKLF et GATA-1 est requise pour permettre une activation maximale du gène beta dans les cellules érythroïdes matures. Un autre facteur impliqué dans la régulation du locus hub est Ikaros. Nous avons étudié son recrutement au locus hub et avons observé que Ikaros est impliqué dans la répression des gènes gamma. Nos résultats montrent aussi que GATA-1 est impliqué dans la répression de ces gènes et qu’il interagit avec Ikaros. Ensemble, Ikaros et GATA-1 favorisent la formation d’un complexe de répression aux promoteurs gamma. Cette étude nous a aussi permis d’observer que Ikaros et GATA-1 sont impliqués dans la répression du gène Gata2. De façon intéressante, nous avons caractérisé le mécanisme de répression du gène Hes1 (un gène cible de la voie Notch) lors de la différenciation érythroïde. Similairement à ce qui a été observé pour les gènes gamma, Hes1 est aussi réprimé par Ikaros et GATA-1. Ces résultats suggèrent donc que la combinaison de Ikaros et GATA-1 est associée à la répression de plusieurs de gènes dans les cellules érythroïdes. Globalement cette thèse rapporte de nouveaux mécanismes d’action de différents facteurs de transcription dans les cellules érythroïdes. Particulièrement, nos travaux ont permis de proposer un modèle pour la régulation des gènes du locus hub lors du développement et de la différenciation. De plus, nous rapportons pour la première fois l’importance de la collaboration entre les facteurs Ikaros et GATA-1 dans la régulation transcriptionnelle de gènes dans les cellules érythroïdes. Des mutations associées à certains des facteurs étudiés ont été rapportées dans des cas de beta-thalassémies ainsi que de leucémies. Nos travaux serviront donc à avoir une meilleure compréhension des mécanismes d’action de ces facteurs afin de potentiellement pouvoir les utiliser comme cibles thérapeutiques.

Carpenter Syndrome: Extended RAB23 Mutation Spectrum and Analysis of Nonsense-mediated mRNA Decay

Carpenter syndrome, a rare autosomal recessive disorder characterized by a combination of craniosynostosis, polysyndactyly, obesity, and other congenital malformations, is caused by mutations in RAB23, encoding a member of the Rab-family of small GTPases. In 15 out of 16 families previously reported, the disease was caused by homozygosity for truncating mutations, and currently only a single missense mutation has been identified in a compound heterozygote. Here, we describe a further 8 independent families comprising 10 affected individuals with Carpenter syndrome, who were positive for mutations in RAB23. We report the first homozygous missense mutation and in-frame deletion, highlighting key residues for RAB23 function, as well as the first splice-site mutation. Multi-suture craniosynostosis and polysyndactyly have been present in all patients described to date, and abnormal external genitalia have been universal in boys. High birth weight was not evident in the current group of patients, but further evidence for laterality defects is reported. No genotype-phenotype correlations are apparent. We provide experimental evidence that transcripts encoding truncating mutations are subject to nonsense-mediated decay, and that this plays an important role in the pathogenesis of many RAB23 mutations. These observations refine the phenotypic spectrum of Carpenter syndrome and offer new insights into molecular pathogenesis. (C) 2011 Wiley-Liss, Inc.

Quality of life related to oral versus subcutaneous iron chelation: a time trade-off study

Objective: To investigate the utility associated with subcutaneous infusion (deferoxamine) compared with once-daily oral administration (deferasirox) of iron chelation therapy.

Methods: Interviews using the time trade-off technique were used to estimate preferences (utility) for health states by finding the point at which respondents were indifferent between a longer but lower quality of life (QoL) and a shorter time in full health. Participants (n = 110) were community-based, 51% women, median age 35 years, from four regions in Sydney, Australia. Respondents rated three health states involving equal outcomes for people with thalassemia but with different treatment modalities for iron chelation; an "anchor state" describing a patient receiving iron chelation without administration mode specified, anchor state plus iron chelation via subcutaneous infusion, and anchor state plus iron chelation through once-daily oral medication.

Results: On an interval scale between 0 (death) and 1 (full health), median (interquartile range) utility of 0.80 (0.65–0.95) for the anchor state, 0.66 (0.45–0.87) for subcutaneous infusion, and 0.93 (0.80–0.97) for once-daily oral administration was obtained. The mean (median) difference of 0.23 (0.27) between the two treatments was statistically significant (Wilcoxon-signed rank test, P < 0.001). Subcutaneous infusion was associated with a mean (median) utility 0.13 (0.14) lower than the anchor state (P < 0.001), and once-daily oral treatment had a utility 0.10 (0.13) higher (P < 0.001).

Conclusion: Community respondents associate oral administration of an iron chelator such as deferasirox with enhanced QoL compared with subcutaneous treatment. Assuming equal safety and efficacy, QoL gains from once-daily oral treatment compared with subcutaneous infusion are significant.

Diagnosis of {alpha}+-thalassemias by determining the ratio of the two {alpha}-globin gene copies by oligonucleotide hybridization and melting curve analysis

Most cases of {alpha}-thalassemia result from large deletions at the {alpha}-globin locus (1). The {alpha}-globin gene cluster contains a tandem array of 2 nearly identical {alpha}-globin genes (HBA; Fig. 1A ) (2). The {alpha}0-thalassemias are characterized by deletions that inactivate both {alpha}-globin genes of a given chromosome, whereas in {alpha}+-thalassemias, one gene remains functional. The most widespread {alpha}+-thalassemias are those designated –{alpha}3.7 and –{alpha}4.2, according to the lengths of the deleted fragments (3).

Caracterização molecular e laboratorial da talassemia beta e da interação hemoglobina s/talassemia beta

Beta thalassemia arises as a consequence of the reduction (β+, β++, βsilent) or absence (β0) of beta globin chain synthesis and results from a number of mechanisms that lead to genetic defects. The inheritance of beta thalassemia is characterized by the existence of heterozygous individuals, compound heterozygotes, homozygotes and those with coinheritance of beta thalassemia allele and other thalassemias and/or hemoglobin variants. The aim of this study was to perform molecular and laboratory characterization of beta thalassemia in heterozygous and homozygous individuals and in those with coinheritance of S beta thalassemia. A total of 48 individuals were included (35 heterozygotes, 4 homozygotes and 9 S beta thalessemia carriers) referred to the Integrated Laboratory of Clinical Analyses of the Federal University of Rio Grande do Norte (UFRN) and the Hematology Ambulatory Facility of the Dalton Barbosa Cunha Hemocenter (Hemonorte Natal, Brazil). Peripheral blood samples form each patient underwent the following laboratory examinations: erythrogram, hemoglobin electrophoresis at alkaline pH, measurements of Hb A2, Fetal Hb and serum ferritin. DNA was extracted using the illustra blood genomicPrep Mini Spin Kit and molecular characterization was performed by the PCR/RFLP technique, which involves digestion with specific restriction enzymes for IVS-1 nt 1 (G®A), IVS-1 nt 6 (T®C) and codon 39 (CAG®TAG) mutations. Of the 35 heterozygotes, 37.1% showed IVS-1 nt 6 mutation, 42.9% IVS-1 nt 1 and 20% were carriers of other mutations not identified by the technique used. The four homozygous patients presented with the IVS-1 nt 6 mutation, while 66.7% of the individuals with S beta thalassemia had the IVS-1 nt 1 mutation. Codon 39 was not detected in any of the patients investigated. Of the thallasemic alleles found, 40.4% were IVS- 1 nt 1, 40.4% IVS-1 nt 6 and 19.2% were not identified. Laboratory data showed that the heterozygotes exhibited microcytosis and hypochromia, evidenced by MCV ranging from 57 to 75fL and MCH from 15.9 to 23.6 pg. Hemoglobin A2 varied between 3.7 and 7.2%. The homogygotes also showed reduced MCV and MCH and elevated HbA2.. Comparison of laboratory data between heterozygous individuals with IVS-1 nt 1 and IVS-1 nt 6 mutations showed that heterozygotes for the IVS1-1 mutation had significantly lower mean MCV and MCH (p = 0.023 and 0.007, respectively) and significantly higher hemoglobin A2 (p < 0.001) when compared to heterozygotes for the IVS-1 nt 6 mutation. PCR/RFLP was useful in identifying the presence or absence of IVS-1 nt 6, IVS-1 nt 1 and codon 39 mutations in most of the patients investigated here. This is the first study conducted in the state of Rio Grande do Norte, Brazil aimed at identifying beta thalassemia mutations and represents an important contribution to the knowledge regarding the molecular profile of beta thalassemia in our country

Amplificação gênica alelo-específica na caracterização das hemoglobinas S, C e D e as interações entre elas e talassemias beta

INTRODUÇÃO: As hemoglobinopatias resultam de alterações hereditárias, sendo prevalentes em muitas regiões do mundo, mas atingem a população brasileira de forma significativa. Elas são decorrentes de alterações em genes estruturais responsáveis pelo aparecimento das hemoglobinas variantes e/ou em genes reguladores, resultando nas talassemias. A identificação dessas patologias tem sido rotineiramente realizada por procedimentos eletroforéticos, contudo nossa experiência laboratorial evidencia que as mesmas nem sempre apresentam resoluções suficientes para a correta caracterização da mutação. CASUÍSTICAS E MÉTODOS: O propósito deste trabalho foi estabelecer uma metodologia válida para a caracterização das hemoglobinas S, C e D em homozigose ou heterozigose, e suas possíveis interações, baseada na amplificação gênica alelo-específica (PCR-AE) com a utilização de primers sense, antisense e primers que se acoplam na posição do alelo mutante e na respectiva posição do alelo normal. RESULTADOS E DISCUSSÃO: Os resultados evidenciaram a validade dessa metodologia na caracterização das mutações, sendo esse procedimento de fácil realização, reprodutível e possível de ser aplicado em um significativo número de amostras.

Ecocardiografia de pacientes talassêmicos sem insuficiência cardíaca em tratamento com transfusões sanguíneas e quelação

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Prevalência de talassemia alfa+ (deleção -3.7) na população adulta do estado do Rio Grande do Norte

Alpha thalassemia, the most common monogenic disorder in the world, is characterized by deletions of one (+-thalassemia) or both alpha genes (0-thalassemia) located on human chromosome 16 (16p13.3). The most common case of +-thalassemia is a deletion of 3.7 kb of DNA (-3.7 deletion). It is most prevalent in African and Middle East regions. In the few studies carried out in Brazilian population -3.7 deletion was the most common deletion, mainly in African descendants. This study was conducted to determine the prevalence of +- thalassemia (deletion 3.7kb) in adult population from Rio Grande do Norte. We obtained blood samples from 713 unrelated individuals of both genders, aged between 18 and 59 years old. All individuals were born in Rio Grande do Norte. The hematological indices were obtained in an automatic cell counter (Micros 60, ABX Diagnostics). The hemoglobin measurement (A2 and Fetal hemoglobin) and the profile confirmation were carried out by high performance liquid chromatography (HPLC) methodology. Genomic DNA was obtained from peripheral blood leukocytes using Illustra Blood GenomicPrep Mini Spin kit and -3.7 deletion was investigated by PCR. Among the 713 individuals studied, 80 (11,2%) presented +- thalassemia: 79 (11,1%) were heterozygous and 1 (0,1%) homozygous for the -3.7 deletion. Considering the ethnic group, negroes showed the greatest prevalence of +-thalassemia (12,5%), followed by mulattoes (12,3%) and caucasian (9,6%). Statistical comparison of hematological parameters between normal individuals and heterozygous to +-thalassemia showed significant differences in RBC (p<0,001), MCV (p<0,001), MCH (p<0,001), Hb A2 (p=0,007) as well as female hemoglobin concentration (p=0,003). This is one of the first studies to research +-thalassemia in general population of Rio Grande do Norte state and these results attest the importance of investigation of this condition to define the etiology of microcytosis and hypochromia.

Valores de ferritina sérica em beta talassemia heterozigota

A low iron level, the commonest nutritional deficiency in the world, is a public health problem in developing countries. on the other hand, an excessive amount of iron is toxic, causing several organic dysfunctions, such as diabetes, cirrhosis, endocrinopathies and heart disease. Researchers have reported an association of iron overload with beta-thalassemia. The aim of this paper was to compare the serum ferritin levels of women with the beta-thalassemia trait. The results of serologic tests of 137 women of childbearing age were analyzed; 63 had the beta-thalassemia trait and 74 had Hb AA. In the beta-thalassemia carriers, the median ferritin value was 51.90 ng/mL and in the non-carriers 31.60 ng/mL (p = 0.0052). Levels of less than 20 and above 150 ng/mL were observed in 28% and 3% of the non-carriers and in 16% and 11% of the carriers, respectively. With these results it is possible to conclude that women in the reproductive age with the beta-thalassemia trait present higher ferritin levels in the northeastern region of São Paulo State. Further studies are necessary to clarify possible genetic and/or environment factors which interfere in iron absorption.

Interação entre Hb C [beta6(A3)Glu>Lys] e IVS II-654 (C>T) beta-talassemia no Brasil

Thalassemias are a heterogeneous group of inherited disorders characterized by a microcytic hypochromic anemia and an imbalance in the synthesis of the globin-chains. Hb C is the second most frequently variant of hemoglobin found in Brazil. The laboratory diagnosis of hemoglobinopathies, including thalassemias, is growing in importance, particularly because of an increasing requirement for neonatal diagnosis of abnormal hemoglobins. Screening tests were carried out using alkaline and acid electrophoresis, globin-chain analysis by cellulose acetate in alkaline pH, isoelectric focusing and HPLC. The molecular characterization was made by PCR-ASO for Hb C and beta thalassemia mutants. Large-scale screening and discriminative methodologies must provide information about the hemoglobin polymorphisms in Brazilian population. HPLC is a powerful tool in these cases. Molecular characterization is important to genetic counseling and clinical management, in particular for the Brazilian population that have an intense racial admixture, with great variability of hemoglobins. In this paper an association between Hb C and beta thalassemia (IVS-II-654) in a black family from Brazil was described.

Dificuldades no diagnóstico laboratorial das hemoglobinopatias

Há vários tipos de hemoglobinopatias que são caracterizados por variantes das hemoglobinas anormais (ex: Hb S, Hb C, Hb Instáveis,etc) e por talassemias (ex: tal. alfa, tal. beta, tal.beta/delta,etc) As hemoglobinopatias são consideradas como uma das doenças genéticas mais comuns em todo o mundo, com prevalência de portadores heterozigotos de seus principais tipos em aproximadamente 5% da população mundial. Devido à heterogenidade clínica e genética dessas alterações genéticas é fundamental estabelecer a investigação laboratorial das diferentes formas de hemoglobinas variantes e de talassemias. Este artigo apresenta as principais dificuldades laboratoriais que envolvem a complexidade molecular das hemoglobinopatias.

Diagnóstico de hemoglobinopatias em recém-nascidos do Hospital de Base de São José do Rio Preto-SP

The neonatal period is considered the most effective for the screening of hemoglobinopathies. This allows prophylaxis and prevention, improving the patient's survival and guidance of parents and heterozygote carriers. The present work aims at the early detection of abnormal hemoglobins, the establishment of standard analysis and to examine the viability of the prevention program. Blood samples were collected by heel stick and from blood cord of children born in the Hospital de Base São José do Rio Preto, from April 1998 to November 1999. Electrophoresis and cytological, biochemical, cromatographic analyses were made for abnormal hemoglobin characterization. A total of 1,478 neonatal blood samples were analyzed in which 14.62% presented with hemoglobins alterations: 3.32% had Hb S; 0.61% had Hb C; 7.44% were suggestive of alpha thalassemia; 1.55% were suggestive of beta thalassemia, and 1.70% had alpha/beta thalassemia interactions. The samples collected from the blood cord showed better results in all analyses while the blood samples collected by heel stick on filter paper, were applicable to only specific methodologies. The routine laboratory methods allowed identification of the thalassemic and variant forms, and isoelectric focusing presented sensitivity only for variant identification in this age range. The suspected cases were reassessed after six months, which permitted genetic counseling of their family members and clinic attendance. A multidisciplinary approach in programs of this kind is fundamental for its success.

Avaliação do perfil hematológico de portadores de talassemia alfa provenientes das regiões Sudeste e Nordeste do Brasil

A talassemia alfa é uma anemia hereditária resultante da síntese deficiente de cadeias alfa, provocando um excesso relativo de cadeias beta, que vão formar tetrâmeros identificados como hemoglobina H (Hb H) no indivíduo adulto. Para direcionar o diagnóstico laboratorial desta anemia, a análise dos índices eritrocitários, a eletroforese em acetato de celulose em pH neutro e a pesquisa de corpos de inclusão de Hb H são essenciais. O objetivo deste estudo foi traçar o perfil hematológico, por meio dos índices eritrocitários, dos portadores de talassemia alfa das regiões Sudeste e Nordeste do Brasil. Foram analisadas 1.010 amostras de sangue periférico após consentimento informado. Os índices eritrocitários como contagem de glóbulos vermelhos (RBC), dosagem de hemoglobina (HGB), hematócrito (HCT), volume corpuscular médio (VCM), hemoglobina corpuscular média (HCM) e concentração de hemoglobina corpuscular média (CHCM) foram fornecidos por aparelhos automatizados com controle de qualidade interno e externo. Para o diagnóstico de talassemia alfa foram utilizados testes de triagem e complementares para talassemias, como eletroforese em pH neutro e pesquisa de corpos de inclusão de Hb H com coloração de azul cresil brilhante. Comparando-se os valores hematológicos observados nos dois grupos, notou-se que, em ambas as regiões, os índices com valores discrepantes foram os níveis de HGB e HCT, sendo a maior freqüência de variação observada entre as mulheres. Nos portadores do fenótipo alfa talassêmico da região Nordeste, todos os índices eritrocitários estavam abaixo dos valores de normalidade. Estes resultados evidenciam a necessidade de melhor avaliação do perfil hematológico de talassemia alfa em diferentes regiões, considerando-se os interferentes ambientais para um diagnóstico mais preciso.

Talassemia β intermediária em gestante

A talassemia β é a forma considerada clinicamente a mais importante dentre as talassemias, em virtude do grau de morbidade e mortalidade, em consequência da anemia hemolítica. O presente relato de caso refere-se a uma gestante portadora da talassemia β intermediária, identificada em programa de rastreamento de anemia hemolítica e tem como objetivo demonstrar a importância do diagnóstico precoce e adequado de uma anemia hereditária, durante o pré-natal. Ressalta também a necessidade de orientação aos portadores em relação aos seus descendentes e a eficiência do acompanhamento por uma equipe multidisciplinar especializada.

What influences Hb fetal production in adulthood?

Human hemoglobin genes are located in α and β globin gene clusters in chromosomes 16 and 11, respectively. Different types of hemoglobin are synthesized according to the stage of development with fetal hemoglobin (α2γ2) (Hb F) being the main hemoglobin in the fetal period. After birth, there is a reduction (to about 1%) in Hb F levels and adult hemoglobin, Hb A (2α2β2), increases to more than 96% of total hemoglobin. However, some genetic conditions whether linked to the β-globin gene cluster or not are associated with high Hb F levels in adults. Among those linked to β-globin are hereditary persistence of fetal hemoglobin, delta-beta thalassemia (δβ-Thalassemia) and the XmnI polymorphism (-158 C > T). Other polymorphisms not related to β-globin gene cluster are known to influence the γ-globin gene expression in adulthood. The most relevant polymorphisms that increase concentrations of Hb F are the HMIP locus on chromosome 6, the BCL11A locus on chromosome 2, the Xp22.2 region of the X chromosome and the 8q region on chromosome 8. Findings from our research group studying genetic factors involved in γ-globin gene regulation in adults without anemia in the northwestern region of São Paulo State showed that high Hb F levels are influenced by the presence of hereditary persistence of fetal hemoglobin mutations and the XmnI polymorphism, suggesting that both genetic alterations characterize the molecular basis of the evaluated population.