A糖基转移酶基因变异所致A_(3)表型1例的遗传学分析

Genetic analysis of an individual with A_(3) phenotype due to variant of A-glycosyltransferase enzyme gene

目的探讨1例A3表型个体的血清学特性和分子机制。方法选取2022年5月12日就诊于中国医科大学附属第四医院的1名27岁汉族女性作为研究对象。使用标准血清学方法检测其ABO血型,通过PCR扩增产物直接测序法鉴定ABO基因及第6~7外显子的单链序列,并使用生物信息学软件对变异位点进行分析。结果检测结果提示该个体为A3表型,其第6、7外显子存在c.261delG、c.467C>T和c.745C>T杂合变异。单链测序结果提示样本存在ABO*A3.07和ABO*O.01.01等位基因,其中ABO*A3.07等位基因在ABO*A1.02等位基因的背景下存在c.745C>T(p.R249W)变异。生物信息学分析预测c.745C>T(p.R249W)为可能有害变异,自由能变化(ΔΔG)值预测其可能影响蛋白稳定性。蛋白模拟模型提示p.R249W可造成α-1,3-N-乙酰半乳糖胺转移酶局部氢键网格的改变。结论α-1,3-N-乙酰半乳糖胺转移酶基因的c.745C>T(p.R249W)变异可能造成酶蛋白结构和功能的失稳,进而导致A抗原表达减弱。

Objective To explore the serological characteristics and molecular mechanism underlying an individual with A3 phenotype.Methods A 27-year-old ethnic Han Chinese woman presented at the Fourth Affiliated Hospital of China Medical University on May 12,2022 was selected as the study subject.ABO blood type was determined with standard serological techniques.The ABO gene was subjected to direct sequencing of PCR products.Exons 6 and 7 of the ABO gene were sequenced using specific primers to determine the haplotypes.Bioinformatic software was used to analyze the structure of the mutant protein.Results Serological typing of the ABO blood group has suggested a rare A3 phenotype.The proband was found to harbor heterozygous c.261delG,c.467C>T and c.745C>T variants by direct sequencing.Single strand sequencing revealed that she has harbored ABO*A3.07and ABO*O.01.01 alleles.The ABO*A3.07 allele has contained a c.745C>T(p.R249W)variant on the background of an ABO*A1.02 allele.The p.R249W substitution was predicted to be probably damaging by the PolyPhen2 software.The free energy change(ΔΔG)value predicted it to have a destabilizing effect on the GTA protein.Meanwhile,modeling of the 3D structure has predicted that the p.R249W amino acid substitution may alter the hydrogen bond network of the GTA protein.Conclusion The p.R249W substitution of theα-1,3-N-acetylgalactosaminyltransferase gene may reduce the antigen expression owing to a great destabilizing effect on the structure and function of the GTA protein.