based on the discovery of the nucleotide and amino acid differences which distinguish the gov a and gov b allelic forms of the membrane glycoprotein cd109 , and which comprise the biallelic gov platelet alloantigen system , compositions and methods are provided for determining the gov genotype and phenotype of individuals . also provided , on the basis of this discovery , are compositions and methods for treating disorders associated with gov alloantigen incompatibility , such as the bleeding disorders post - transfusion purpura , post - transfusion platelet refractoriness , and neonatal alloimmune thrombocytopenia . the two allelic forms of cd109 differ by a single amino acid . the gov a allelic form has tyr at amino acid position 703 in the cd109 sequence . the gov b allelic form has ser at the same position . this amino acid difference is due to a single change , from a for the gov a allele to c for the gov b allele , in the cd109 gene .