汕头市户籍人群α和β地中海贫血的分子流行病学调查

Molecular Epidemiological Analysis of α and β Thalassemiain Shantou City of Guangdong Province

目的调查汕头市户籍人群中α和β地中海贫血(简称地贫)的发生率、基因突变类型及其构成比。方法以整群抽样法收集1034份其父母均为汕头市户籍的新生儿脐血和1572份双方均为汕头市户籍的成人婚检或孕检对象的静脉血,分别进行α地贫和β地贫调查。所有样品均进行红细胞(RBC)参数和血红蛋白(Hb)电泳分析,以脐血中出现HbBart5s作为诊断α-地贫的阳性参考指标;以静脉血平均红细胞体积(MCV)≤80fl,HbA2≥3.5%作为诊断β-地贫的阳性参考指标。再应用gap-PCR和反向点杂交(RDB)技术对表型阳性样品进行α-地贫基因和β-地贫基因定型,"未知"样品则进行DNA直接测序分析。同时对HbBart5s阴性的脐血样品进行两种常见静止型α-地贫基因(-a3.7和-a4.2)的分子筛查。结果在1034例脐血标本中检出7种α-地贫基因型共58例,等位基因59个,α-地贫基因携带率为5.71%(59/1034)。其基因型构成比:-a3.7/aa为48.3%,--SEA/aa为29.3%,-a4.2/aa为12.1%,--THAI/aa为3.5%,--SEA/--SEA、aCSa/aa和a1CD118+TCA各为1.7%。成人静脉血1572例标本中检出β-地贫基因携带者共15例(其中1例CD41/42(-TCTT)合并-a3.7),β-地贫基因携带率为0.95%(15/1572)。共检出5种β-地贫基因,其构成比:IVS-2-654(C→T)和-28(A→G)各为26.7%,CD41/42(-TCTT)为20.0%,CD17(A→T)为13.3%,βECD26(G→A)为6.7%。结论阐明了汕头市户籍人群中α和β地中海贫血基因的携带率、基因突变类型及其分布特征。该结果为进行遗传咨询和制定该地区基于大人群筛查的预防计划提供了有价值的基础资料。

Objective To investigate the gene frequency and the pattern of mutation of α-thalassemia （α-thal） and β-thalassemia （β-thal） in Shantou city. Method Cluster sampling was used in this study. A total of 1034 of neonatal cord blood samples were collected for a prevalence study of α-thal, and a total of 1572 samples of premarriage or pregnant women and their spouses were collected for a β-thal prevalence survey. All subjects included in this study were registered in Shantou city. A complete blood count as well as hemoglobin electrophoresis analysis was performed in all of samples for phenotyping of α and β-thals. Those with Hb Bart＇s for α-thal and those with both microcytosis （MCV≤80 fl） and elevated levels of HbA2 （≥3.5%） for β-thal were further studied by DNA analysis. The α-thal and β-thal chromosomes were determined by using gap-PCR and reverse dot blot （RDB） assays respectively in the positive samples with α-thal or β-thal determinants. Unknown positive samples were analyzed directly with DNA sequencing. In addition, -a^3.7 and -a^4.2 alleles were screened using gap-PCR in all cord blood samples. Result Of all 1034 cord blood samples, including 7 well-known α-globin genotypes and 1 unknown β- globin genotype, 58 samples with 59 alleles were detected. The carrier rate of α-thalassemia in Shantou population is 5.71% （59/1034）. The frequency of each genotype of the 7 α-thalassemia mutations was calculated to be 48.3% for -a^3.7/aa, 29.3% for --^SEA/aa, 12.1% for -a^4.2/aa, 3.5% for --^THAI/aa, and 1.7% for each --^SEA/--^SEA, a^CSa/aa, and a1CD118＋TCA. Of all 1572 adult samples, including 5 well-known type of β-thalassemia mutation and 1 unknown type, 15 alleles were detected, and one of the samples was CD41/42 compounded with -a^3.7. The carrier rate of β-thalassemia in Shantou population was 0.95% （15/1572）. The gene frequency of the 5 β-thalassemia mutations was calculated to be 26.7% for IVS-2-654 and -28, 20.0% for CD41/42, 13.2% for CD17, and 6.7% for βECD26. Conclusion The prevalence, mutation spectrum and mutant allele constitution of α-thai and β-thal in Shantou population are studied. The results would be useful for genetic counseling and for the future design of project for the prevention of thalassemia based on a larger scale population screening in this area.