Serologic Variability of the $A^{var}$ (784G＞A) and Its Property of Different Expression Depending on Co-inherited ABO Allele

Background: A allele, , characterized by a 784G＞A polymorphism (Asp262Asn) has been identified only in Korean donors. This study evaluated the serological and genetic characteristics of thirteen samples with newly identified allele. Methods: This study examined 10 samples with the allele including 4 members from a family, who were randomly obtained from blood donors recruited at Gwangju-Chonnam Red Cross Blood Center, and patients at the Chonnam National University Hospital. Routine ABO serologic tests, ABO genotyping using an allele specific polymerase chain reaction (AS-PCR), and the sequencing of exon 6 and 7 of ABO gene were performed on all samples. In addition, sequencing of exon 1∼5 of the ABO gene was carried out on two randomly selected samples. Results: The allele was identified in nine and one O (II-1 of the family study) sample. Eight of these nine individuals showed 1+ agglutination with the monoclonal anti-A reagents on forward typing but one sample showed no agglutination. Weak anti-A was detected in all sera. From the family study, the allele, which was transmitted from the propositus through her descendant (II-1, II-3 and III-1), produced either the weak A phenotype when inherited with a B allele or the O phenotype when inherited with an O allele. Conclusion: erythrocytes showed different agglutination patterns to anti-A. Different expressions (possible allelic enhancement) were observed depending on the co-inherited ABO alleles from samples with the allele. (Korean J Blood Transfusion 17(1) : 61∼70, 2006)