台灣A2B血型之基因分型

ABO血型的對偶基因主要分為三種：A對偶基因、B對偶基因、O對偶基因。ABO血型的對偶基因位於人類第9對染色體上9q34.1~q34.2位置，其中包含了7個外顯子(exon)，18 kb的基因組(genomic DNA)。其中第7個外顯子長度最長，而在O對偶基因的第6個外顯子有一個核甘酸缺失因而造成酵素活性的消失。A對偶基因與B對偶基因之間有7個核甘酸的差異，其中造成了四種胺基酸的不同，分別在第176位置精胺酸轉換成甘胺酸(Arg176Gly)，第235位置甘胺酸轉換成絲胺酸(Gly235Ser)，在第266位置白胺酸轉換成甲醯胺酸(Leu266Met)，在第268位置甘胺酸轉換成丙氨酸(Gly268Ala)。而O對偶基因與A對偶基因的區別在於O對偶基因在核甘酸第261位置缺少了一個鳥糞嘌呤(guanine)因而造成了核甘酸序列位移而缺乏酵素活性。利用分子生物學方法來協助分析ABO亞血型的基因型，以解決一些利用血清學分析之ABO血型結果矛盾已經是廣泛被利用的。我們與高雄捐血中心合作，由高雄捐血中心在2004年時收集到台灣中南部地區的A2B亞血型捐贈者共127位，其中的61位已經利用分子生物學方法檢測其基因型，藉以觀察A2B亞血型在台灣的所有AB型當中是否佔有如此高的比例。所有A2B的表現型是利用血清學方法做檢測。利用聚合酶連鎖反應-限制長度多型性(polymerase chain reaction-restriction fragment length polymorphism)的方法，針對鹼基261以及鹼基703的位置，作ABO對偶基因的O基因，B基因做初步篩檢，基於血型O型在鹼基第261位置的鳥糞嘌呤(guanine)是缺損的，而在鹼基703的位置，A 對偶基因與O對偶基因都是鳥糞嘌呤(guanine)，B對偶基因則是腺嘌呤(adenine)的這些特性，先使用限制酶做初步篩檢。接著做A2對偶基因的各種基因型檢測，包括A201，A202， A203， A204， A205， A206， A207，A208與A209的檢測，使用的方法也是聚合酶連鎖反應-限制長度多型性(polymerase chain reaction-restriction fragment length polymorphism)。進一步確認的方法則是利用基因選殖後做定序。結果在61位捐贈者的檢體中有55位是屬於A205與B allele這樣的對偶基因組合(佔了90%)，兩位是A201與 B allele的對偶基因組合。另外四位是具有cis-AB allele，其中兩位是cis-AB04與O allele對偶基因組合，一位是cis-AB01與O allele對偶基因組合，最後一位則是cis-AB02與B allele對偶基因組合。根據我們的研究結果顯示，在台灣血型表現型為A2B的人，他們的基因型大部分都屬於A205與B allele的對偶基因組合，而A205， A201與cis-AB02 alleles是首次在台灣報告。

關鍵字

A2B亞血型

並列摘要

The ABO locus has three main allelic forms: A allele, B allele, and O allele. It is located on chromosome 9 at 9q34.1-q34.2 and contains 7 exons that span more than 18 kb of genomic DNA. Exon 7 is the largest and contains most of the coding sequence. Exon 6 contains the deletion that is found in most O alleles and results in a loss of enzymatic activity. The A and B alleles differ from each other by seven nucleotide substitutions, which result in A and B transferases that differ by four amino acids (Arg176Gly, Gly235Ser, Leu266Met, Gly268Ala). The O allele differs from the A allele by deletion of guanine at position 261. The deletion causes a frameshift and results the lacking of enzymatic activity. Molecular genotyping of the ABO alleles has been widely used in ABO subgroups analysis and solved the rare ABO blood grouping discrepancies. One hundred and twenty-seven A2B donors were found from the 8448 AB blood donors collected from two blood centers in 2004 in Taiwan. Sixty-one A2B donors were analyzed by means of molecular methods to investigate the alleles resulting in the A2B phenotype distribution in Taiwan. The A2B phenotype was identified by serological test. The polymerase chain reaction-restriction fragment length polymorphism method was used to screen ABO alleles at nucleotide (nt) 261 and 703 based on the nt differences of the ABO alleles. The subgroups of the A2 allele were determined by the PCR-RFLP method. The discrepancies between the A2B phenotype and genotype of the A2B were then studied by subcloning and nucleotide sequence analyses. Fifty-five of 61 donors (90%) are A205 and B allele; two are A201 and B allele. Four cases were heterozygotes of cis-AB allele and O/B alleles. Two were cis-AB04 and O allele, one was cis-AB01 and O allele, and the other was cis-AB02 and B allele. Most A2B genotypes belong to A205 and B allele in Taiwan. The A205, A201, and cis-AB02 alleles are being reported for the first time in Taiwan.

並列關鍵字

A2B genotypes

參考文獻

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