Gonçalves I, Ducrocq R, Lavinha J, Nogueira P J, Peres M J, Picanço I, Correia E, Reis A B, Silva C, Krishnamoorthy R, Almeida L O
Laboratório de Genética Molecular, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Monte da Caparica, Portugal.
Am J Hematol. 1998 Apr;57(4):269-76. doi: 10.1002/(sici)1096-8652(199804)57:4<269::aid-ajh1>3.0.co;2-s.
Beta thalassemia and Hb Lepore heterozygotes included in this study exhibit fetal hemoglobin levels varying from trace quantities to 14% (1.74 g/dl) of total hemoglobin in the adult. In this work, we have examined the correlation of DNA sequence polymorphisms with the observed HbF level. The analysis of polymorphic markers within the beta globin cluster in 39 individuals heterozygous for beta thalassemia or Hb Lepore confirms the previous findings for homozygous beta thalassemia: the presence of both an (AT)9 T5 sequence configuration at position -540 of the beta globin gene and a (C --> T) variation at -158 of the Ggamma globin gene is associated with elevated expression of HbF. However, at least one defective beta globin gene is required to reveal this association. The best evidence is from the study of individuals heterozygous for Hb Lepore with various levels of HbF. In these individuals it was possible to explore the effect of a single (AT)x Ty motif (the other being absent from the rearranged Lepore chromosome) on HbF expression. The presence of the (AT)9 T5 configuration increases HbF level from a median of 0.515 g/dl observed in (AT)7 T7 subjects, to 1.39 g/dl. We confirm the existence of linkage disequilibrium between the (C --> T) variation at -158 of Ggamma gene and the (TG)13 configuration at the second intervening sequence (IVS-2) of Agamma gene and identify two new polymorphisms in this region: (TG)7 (CG)5 (TG)8 linked to haplotype V and (TG)8 (CG)5 (TG)10 linked to haplotype II. This study suggests that two distinct regions of the beta cluster, whether in cis or in trans to each other, can interact to enhance HbF expression when a beta thalassemic determinant is present in heterozigosity.
本研究纳入的β地中海贫血和血红蛋白Lepore杂合子患者，其胎儿血红蛋白水平在成人中占总血红蛋白的比例从微量到14%（1.74 g/dl）不等。在本研究中，我们检测了DNA序列多态性与观察到的HbF水平之间的相关性。对39例β地中海贫血或血红蛋白Lepore杂合子个体的β珠蛋白基因簇内多态性标记的分析，证实了之前对纯合β地中海贫血的研究结果：β珠蛋白基因-540位点存在(AT)9 T5序列构型以及Gγ珠蛋白基因-158位点存在(C→T)变异，均与HbF表达升高相关。然而，至少需要一个缺陷性β珠蛋白基因才能揭示这种关联。最有力的证据来自对不同HbF水平的血红蛋白Lepore杂合子个体的研究。在这些个体中，可以探究单个(AT)x Ty基序（另一个在重排的Lepore染色体上不存在）对HbF表达的影响。(AT)9 T5构型的存在使HbF水平从(AT)7 T7受试者中观察到的中位数0.515 g/dl增加到1.39 g/dl。我们证实了Gγ基因-158位点的(C→T)变异与Aγ基因第二内含子（IVS-2）的(TG)13构型之间存在连锁不平衡，并在该区域鉴定出两个新的多态性：与单倍型V连锁的(TG)7 (CG)5 (TG) VIII和与单倍型II连锁的(TG)8 (CG)5 (TG)10。本研究表明，当β地中海贫血决定因素以杂合状态存在时，β基因簇中两个不同的区域，无论彼此是顺式还是反式，都可以相互作用以增强HbF表达。
