A tyrosine703serine polymorphism of CD109 defines the Gov platelet alloantigens

Abstract

The biallelic platelet-specific Gov antigen system—implicated in refractoriness to platelet transfusion, neonatal alloimmune thrombocytopenia, and posttransfusion purpura—is carried by the glycosylphosphatidylinositol (GPI)–linked protein CD109. The recent identification of the human CD109 complementary DNA (cDNA) has allowed the molecular nature of the Gov alleles to be elucidated. By using reverse transcriptase–polymerase chain reaction (RT-PCR) to amplify CD109 cDNAs from 6 phenotypically homozygous Govaa and Govbb individuals, we have determined that the Gov alleles differ by an A to C single nucleotide polymorphism (SNP) at position 2108 of the coding region, resulting in a Tyr/Ser substitution at CD109 amino acid 703. Allele-specific PCR sequence-specific primers (SSP), PCR-restriction fragment length polymorphism, and real-time PCR studies of 15 additional donors (5 Govaa, 5 Govbb, and 5 Govab) confirmed that this SNP correlates with the Gov phenotype. In addition, Chinese hamster ovary cells transiently expressing nucleotide 2108 A>C CD109 cDNA variants were recognized specifically by allele-specific Gov antisera, indicating that this polymorphism defines the Gov alloantigenic determinants. Real-time PCR was then used to genotype 85 additional Gov phenotyped donors. In all but 3 cases, genomic testing concurred with the Gov phenotype. Repeat testing corrected 2 of these discrepancies in favor of the genotyping result. The third discrepancy could not be resolved, likely reflecting low-level CD109 expression below the sensitivity of the phenotyping assay. We conclude that the Gov alleles are defined by a 2108 A>C SNP that results in a Tyr703Ser substitution of CD109 and that genotyping studies are more accurate for Gov alloantigen determination than are conventional serologic methods.