中国人群中少见β地中海贫血家系的分子遗传学特征分析

Analysis of the molecular characterization of a Chinese pedigree with rare β thalassemia genotype

目的 探讨在中国人群中发现的1个少见β地中海贫血家系的分子遗传学特征.方法 采用标准的血液学分析技术检测先证者及家系成员红细胞参数,包括RBC、Hb、MCV、MCH、MCHC和RDW,进行表型诊断.利用SPIFE快速自动电泳分析系统检测其血红蛋白组分Hb A、Hb A2和Hb F.采用RDB技术检测β地中海贫血基因突变,并进一步进行克隆测序及家系分析,明确突变位点.结果 先证者及其父亲红细胞参数呈典型的小细胞低色素改变,MCV和MCH均降低,MCV分别为79.1 fl及63.1 fl,MCH为19.9 pg及20.9 pg;而先证者母亲的MCV及MCH均正常.先证者及其父亲Hb A2增加,分别为5.66%及5.60%,提示其为轻型β地中海贫血基因携带者.进一步的基因分析表明,先证者在一个β珠蛋白基因同时发生CD41/42（-TTCT）和转录区＋40～＋43缺失突变,诊断为β41/42、CAP/βA基因型的轻型地中海贫血患儿,其父母基因型分别为β41/42、CAP/βA 和βA/βA.结论 先证者在一个β珠蛋白基因同时发生CD41/42（-TTCT）和转录区＋40～＋43缺失突变,β41/42、CAP/βA基因型的发现丰富了中国人群β珠蛋白基因突变研究数据。

Objective To investigate the molecular characterization of a Chinese pedigree with rare β thalassemia genotype.Methods Phenotypic analysis was performed using standard hematological tests to measure red blood cell parameters, including RBC,Hb,MCV,MCH,MCHC and RDW.SPIFE automatic Hb agarose gel electrophoresis instrument was used to measure hemoglobin fraction Hb A,Hb A2 and Hb F.The alleles of β thalassemia mutation were determined by RDB assay, and then cloning and sequencing were performed to define the mutation sites.Results The proband and his father had typical microcytic hypochromic anemia with low MCV and MCH（79.8, 63.1 fl and 19.9, 20.9 pg, respectively） and high level of Hb A2 （5.66% and 5.60%, respectively）.The proband′s mother had normal MCV and MCH. β thalassemia mutation analysis with RDB assay showed that the proband had thalassemia minor resulting from double mutations on one globin gene.One showed codons 41/42 （-TTCT） mutation and the other was CAP mutation from positions ＋40 to ＋43 in the promoter region.These two mutations were inherited from his father.The genotype of the proband and his father was β41/42、CAP/βA ,and the genotype of his mother was βA/βA.Conclusions It′s rare that double mutations occur on single β globin gene, with one mutation on CD41/42（-TTCT） and the other mutation from positions ＋40 to ＋43 relative to the mRNA cap site in the promoter region.The findings enrich knowledge of the mutation spectrum of β thalassemia.