P40
A Novel Variant in the Ok Blood Group System

Introduction  Oka (OK1), the only antigen of the Ok blood group system, occurs with a very high frequency in all populations studied. Oka is located on the immunoglobulin superfamily glycoprotein CD147, also known as M6 leukocyte activation antigen, basigin (BSG) or extracellular matrix metalloproteinase inducer (EMMPRIN), which is encoded by the CD147 gene located on chromosome 19p13.3. The only known polymorphic forms of Oka are the extremely rare Ok(a‐) phenotypes described in eight families of Japanese origin (Spring et al. (1997) Eur. J. Immunol. 27, 891–897) and one Caucasian individual of Iranian background (Karamatic Crew et al. (2003) Transfusion Med 13(1), P32). In both cases, the molecular basis of the Ok(a‐) phenotype were unique missense point mutations leading to amino acid changes within the carrier protein.Case Study and Methods  We investigated a case of a prenatal patient of Hispanic origin whose serum contained an antibody to an unknown high frequency antigen, with a suspected Oka specificity. There was no known history of transfusion or previous pregnancies. Serological tests were performed by standard agglutination techniques. Genomic DNA was isolated from whole blood of the patient and all the exons of the CD147 gene were amplified by PCR and directly sequenced.Results  The patient's serum reacted with all tested cells of rare and null phenotypes, with the exception of three examples of Ok(a‐) cells. Her red cells were positive with all examples of anti‐Oka tested, indicating a novel Oka phenotype. Sequencing of CD147 revealed a novel homozygous mutation in exon 2 178G>A, causing Val60Met change in CD147 protein.Conclusion  We report the second non‐Japanese individual with a variant Oka phenotype. We have confirmed that patient's serum contained an antibody associated with Oka, although it was different from the anti‐Oka examples described previously. This rare novel Oka variant results from a single point mutation in CD147 leading to a Val60Met change. This new Oka variant and the distribution of the mutations within CD147 indicate a more complex blood group system.