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Identificação de modificadores genéticos em crianças com anemia de células falciformes numa área endémica de Malária, Angola
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Introdução: A Anemia de Células Falciformes (ACF) é uma doença genética de transmissão autossómica recessiva que resulta de uma mutação na posição 6 da cadeia de β-globina com substituição de um ácido glutâmico por valina. É a doença monogénica mais frequente a nível mundial com elevada prevalência em África, caracterizada por fenómenos vaso-oclusivos e hemólise crónica. As manifestações clínicas são muito heterogéneas, de gravidade variável entre os pacientes devido a factores ambientais e a existência de importantes modificadores genéticos. Uma das intervenções terapêuticas é o uso da Hidroxiureia (HU) que tem como acção principal a indução da hemoglobina fetal, embora com resposta variada entre os pacientes. Objetivo: O objectivo deste trabalho consistiu na identificação de modificadores genéticos e no estudo da resposta à terapêutica com HU em crianças com ACF residentes em Angola, onde a malária é endémica. Metodologia: O estudo incluiu 215 crianças dos 3 aos 12 anos de idade tendo sido feita a sua caracterização genética pela a análise de regiões polimórficas em genes associados à variação da HbF, à adesão celular (VCAM1 e CD36), tónus vascular (NOS3) e hemoglobinização dos eritrócitos (HBA). Também foi feita, durante a medicação com HU, a análise longitudinal dos fenótipos clínicos, hematológicos e bioquímicos e suas possíveis interações com a infecção malárica. Resultados: Os resultados demonstraram uma significativa heterogeneidade fenotípica entre os pacientes quanto ao início das manifestações clínicas, número de transfusões e de internamentos. A análise longitudinal para além de avaliar a influência da infecção malárica na evolução clínica da ACF permitiu identificar, pela análise comparativa nas duas fases do estudo (pré e pós-HU), os benefícios da medicação. Os estudos de associação entre as variantes identificadas e os fenótipos permitiram estabelecer que a evolução clínica mais suave foi associada à co-herança da deleção -3,7kb da α-talassémia, à presença do polimorfismo rs1041163 T>C no gene VCAM1 associado à menor taxa de hemólise, variantes rs4671393_A, rs11886868_C, rs1427407_T e rs7557939_G, no gene BCL11A, variantes rs7483144_A no gene HBG2 e rs66650371_T no gene HBS1L-MYB associados a níveis mais altos de de HbF. A maior gravidade da doença foi associada a níveis mais baixos de HbF encontrados no haplótipo CAR/CAR, variantes rs2070744_C, no gene NOS3 e rs1041163 T>C no gene VCAM1 associadas a maior taxa de hemólise e, as variantes rs1984112_G e rs1413661_C no gene CD36 estiveram associados à gravidade da anemia. Conclusão: Este estudo permitiu conhecer a heterogeneidade clínica e laboratorial da ACF em crianças angolanas, confirmar os benefícios da HU permitindo assim a aquisição de bases para a implementação de directrizes do uso da HU num contexto de alta prevalência da doença e recursos financeiros limitados. Os estudos de associação genótipo-fenótipo contribuíram para o melhor conhecimento da complexidade que é a ACF.
Abstract Introdution: Sickle Cell Anemia (SCA) is an autosomal recessive genetic disease that results from a mutation in position 6 of the β-globin chain with the replacement of a glutamic acid by valine. It is the most common monogenic disease worldwide with a high prevalence in Africa, characterized by vaso-occlusive phenomena and chronic hemolysis. Clinical manifestations are very heterogeneous, with varying severity between patients due to environmental factors and the existence of important genetic modifiers. One of the therapeutic interventions is the use of Hydroxyurea (HU), whose main action is the induction of fetal hemoglobin, although with a varied response between patients. Objective: The objective of this work was to identify genetic modifiers and study the response to HU therapy in children with ACF living in Angola, where malaria is endemic. Methodology: The study included 215 children aged 3 to 12 years and their genetic characterization was carried out by analyzing polymorphic regions in genes associated with HbF variation, cell adhesion (VCAM1 and CD36), vascular tone (NOS3) and hemoglobinization of the erythrocytes (HBA). During medication with HU, a longitudinal analysis of clinical, hematological and biochemical phenotypes and their possible interactions with malaria infection was also carried out. Results: The results demonstrated significant phenotypic heterogeneity among patients regarding the onset of clinical manifestations, number of transfusions and hospitalizations. The longitudinal analysis, in addition to evaluating the influence of malaria infection on the clinical evolution of ACF, made it possible to identify, through comparative analysis in the two phases of the pre- and post-HU study, the benefits of the medication. Association studies between the identified variants and the phenotypes allowed us to establish that the smoother clinical evolution was associated with the co-inheritance of the -3.7kb deletion of α-thalassemia, the presence of the rs1041163 T>C polymorphism in the VCAM1 gene associated with lower hemolysis rate, variants rs4671393_A, rs11886868_C, rs1427407_T and rs7557939_G, in the BCL11A gene, variants rs7483144_A in the HBG2 gene and rs66650371_T in the HBS1L-MYB gene associated with higher levels of HbF. The greater severity of the disease was associated with lower levels of HbF found in the CAR/CAR haplotype, variants rs2070744_C, in the NOS3 gene and rs1041163 T>C in the VCAM1 gene associated with a higher rate of hemolysis and, the variants rs1984112_G and rs1413661_C in the CD36 gene were associated with the severity of anemia. Conclusion: This study contributed to the understand the clinical and laboratory heterogeneity of SCA in Angolan children, confirming the benefits of HU, thus allowing the acquisition of bases for the implementation of guidelines for the use of HU in a context of high prevalence of the disease and limited financial resources. Genotype-phenotype association studies have contributed to a better understanding of the complexity that is SCA.
Abstract Introdution: Sickle Cell Anemia (SCA) is an autosomal recessive genetic disease that results from a mutation in position 6 of the β-globin chain with the replacement of a glutamic acid by valine. It is the most common monogenic disease worldwide with a high prevalence in Africa, characterized by vaso-occlusive phenomena and chronic hemolysis. Clinical manifestations are very heterogeneous, with varying severity between patients due to environmental factors and the existence of important genetic modifiers. One of the therapeutic interventions is the use of Hydroxyurea (HU), whose main action is the induction of fetal hemoglobin, although with a varied response between patients. Objective: The objective of this work was to identify genetic modifiers and study the response to HU therapy in children with ACF living in Angola, where malaria is endemic. Methodology: The study included 215 children aged 3 to 12 years and their genetic characterization was carried out by analyzing polymorphic regions in genes associated with HbF variation, cell adhesion (VCAM1 and CD36), vascular tone (NOS3) and hemoglobinization of the erythrocytes (HBA). During medication with HU, a longitudinal analysis of clinical, hematological and biochemical phenotypes and their possible interactions with malaria infection was also carried out. Results: The results demonstrated significant phenotypic heterogeneity among patients regarding the onset of clinical manifestations, number of transfusions and hospitalizations. The longitudinal analysis, in addition to evaluating the influence of malaria infection on the clinical evolution of ACF, made it possible to identify, through comparative analysis in the two phases of the pre- and post-HU study, the benefits of the medication. Association studies between the identified variants and the phenotypes allowed us to establish that the smoother clinical evolution was associated with the co-inheritance of the -3.7kb deletion of α-thalassemia, the presence of the rs1041163 T>C polymorphism in the VCAM1 gene associated with lower hemolysis rate, variants rs4671393_A, rs11886868_C, rs1427407_T and rs7557939_G, in the BCL11A gene, variants rs7483144_A in the HBG2 gene and rs66650371_T in the HBS1L-MYB gene associated with higher levels of HbF. The greater severity of the disease was associated with lower levels of HbF found in the CAR/CAR haplotype, variants rs2070744_C, in the NOS3 gene and rs1041163 T>C in the VCAM1 gene associated with a higher rate of hemolysis and, the variants rs1984112_G and rs1413661_C in the CD36 gene were associated with the severity of anemia. Conclusion: This study contributed to the understand the clinical and laboratory heterogeneity of SCA in Angolan children, confirming the benefits of HU, thus allowing the acquisition of bases for the implementation of guidelines for the use of HU in a context of high prevalence of the disease and limited financial resources. Genotype-phenotype association studies have contributed to a better understanding of the complexity that is SCA.
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Microbiologia DST Genética Malária Hidroxiureia Hemoglobina fetal Anemia de células falciformes Modificadores genéticos