ABO chimerism with a minor allele detected by the peptide nucleic acid-mediated polymerase chain reaction clamping method.

Abstract

Discrepancy of results of ABO groups between red cell testing and serum testing is a significant issue in transfusion medicine1. One of its reported causes is blood chimerism, which shows mixed-field agglutination. However, mixed-field agglutination can be seen in various situations, including ABO-incompatible stem cell transplantation, recent transfusions of type-O red blood cells in a non-O recipient, and rare ABO subgroups such as B3 and chimera. Several molecular approaches have been employed to identify chimerism, namely ABO genotyping, human leucocyte antigen typing and DNA short tandem repeat assays2. These methods can typically detect three or more alleles of a chimera. However, some chimeras with a minor allele population might be overlooked because of preferential amplification of the major allele during ordinary polymerase chain reaction (PCR) analysis. We report a case of blood chimerism in which B red cells accounted for less than 1% of the whole population. The B allele in peripheral blood mononuclear cells could not be identified by direct sequencing of ordinary PCR product involving exons 6 and 7 of the ABO gene, but was revealed using peptide nucleic acid (PNA)-mediated PCR clamping.