α-1,3-N-乙酰半乳糖胺等位基因421T＞C突变导致A抗原弱表达

摘要

Objective To investigate the molecular basis of an individual featuring weak A phenotype of ABO blood group system.Methods Serologic investigations,serum transferases activity assay and absorption elution test were carried out to identify the ABO blood group.The 7 exons and flanking introns of ABO glycosyltransferase gene were amplified with polymerase chain reaction (PCR).The products were sequenced bidirectinally following enzyme digestion.Haplotypes of exons 6 and 7 of the ABO gene were analyzed.Results A weak A antigen was identified on red blood cells of the proband.Eight heterozygous sites in exons 6 and 7 (261delG 297A/G,421C/T,467C/T,646T/A,681G/A,771C/T,829G/A) of the ABO gene were identified.Based on haplotype analysis,one allele was determined as O02,while a novel mutation 421T＞C was identified in another allele,which resulted in the amino acid change Ser141Pro of the A glycosyltransferase.Conclusion Above results suggested that amino acid substitutions resulted from a novel mutation 421T＞C of the ABO gene may decrease the enzymatic activity and result in the weak A phenotype.%目的 探讨1例ABO血型系统A变异型的分子遗传学背景.方法 采用血清学方法鉴定ABO血型,测定血浆α-1,3-N-乙酰半乳糖胺转移酶的活性,用PCR扩增ABO基因的7个外显子及启动子序列,测序分析第7外显子单倍体.结果 先证者红细胞ABO血型为A弱表现型,ABO基因全编码区测序发现8处核苷酸杂合位点,分别为第6外显子的261delG缺失和297A/G、第7外显子的421C/T、467C/T、646T/A、681G/A、771C/T以及829G/A杂合变异.单链测序分析提示,其中1条为O02等位基因,另一个等位基因除421T＞C和467C＞T突变外,其他变异位点与A101等位基因一致.421T＞C突变可导致A糖基转移酶第141位丝氨酸替换为脯氨酸(Ser141Pro).结论 产生弱A表型的原因可能是由于A糖基转移酶基因421T＞C突变引起编码的氨基酸改变,使α-1,3-N-乙酰半乳糖胺转移酶活性减弱,导致A抗原弱表达.