Objective: To analyze the different subtypes caused by c.721C>T substitution in the exon 7 of the ABO gene, and to investigate the related molecular mechanism of different antigens expression.
Methods: ABO subtypes in 7 samples were identified by standard serological methods. The exons 6, 7, and adjacent intron of ABO gene were amplified by Polymerase Chain Reaction (PCR), and the PCR products were analyzed by direct DNA sequencing and cloning sequencing.
Results: ABO subtypes phenotypes were AW (1 case), BW (3 cases), ABW (2 cases), A2 or Aint (1 case). The result showed that the 7th exon of ABO gene was c.721C>T variety based on A1.02, B1.01, and O.01.02; the alleles were AW.43（1 case）, BW.03（5 cases） and O.01.07（1 case）, ABO genotypes were ABO*AW.43/O.01.02 (1 case) , ABO*BW.03/O.01.02 (3 cases), ABO*A1.02/BW.03 (2 cases), and ABO*A2.05/O.01.07 (1 case).
Conclusion: c.721C>T substitution in the ABO gene causes p.Arg241Trp exchange resulting in the decreasing of GTA or GTB activities and weaker antigen expression. O.01.07 is a null allele which cannot form a functional catalytic enzyme has no effect on A2 subtype antigen expression.
题目: ABO基因第7外显子c.721C>T变异导致ABO亚型的研究.
目的: 分析ABO基因第7外显子c.721C>T变异导致的不同亚型，探讨影响抗原表达的分子机制.
方法: 通过标准血型血清学方法鉴定7例样本的ABO亚型，应用聚合酶链反应（polymerase chain reaction, PCR）法扩增ABO基因第6、7外显子及相关内含子，并进行直接DNA测序和克隆测序.
结果: 7例ABO表型分别为：AW 1例、BW 3例、ABW 2例、A2或Aint 1例。测序发现，ABO基因第7外显子分别在A1.02、B1.01和O.01.02等位基础上发生了c.721C>T变异，等位基因分别为AW.43（1例）、BW.03（5例）和O.01.07（1例），基因型分别为ABO*AW.43/O.01.02 （1例）、ABO*BW.03/O.01.01（3例）、ABO*A1.02/ BW.03 （2例）和ABO*A2.05/ O.01.07 （1例）.
结论: ABO基因c.721C>T变异引起241位氨基酸精氨酸（Arg）被色氨酸（Trp）替换，导致α-1,3-N-乙酰半乳糖胺基转移酶（GTA）或α-1,3-D-半乳糖基转移酶（GTB）活性降低，抗原表达减弱。在O.01.02基础上产生c.721 C>T变异形成的O.01.07等位基因，是一个无效等位基因，不能形成有催化功能的酶，对A2亚型抗原的表达无影响.