title: Blood grouping discrepancies between ABO genotype and phenotype caused by O alleles.
abstract: OBJECTIVE
  In the modern transfusion service, analysis of the ABO allele underlying a donor or recipient's A or B subtype phenotype is becoming a mainstream adjunct to the serological investigation. Although an analysis of the ABO gene can be helpful in establishing the nature of the subtype phenotype, numerous confounding factors exist that can lead to a discrepancy between the genotype and the observed phenotype.
  
  
  RESULTS
  Although the most common group O alleles share a common crippling polymorphism, a growing number of alleles feature other polymorphisms that render their protein nonfunctional yet are similar enough to the consensus A allele that an errant phenotype would be predicted from the genotype, if the genotyping method was not specifically designed for their detection. Some of these O alleles might actually encode a protein with weak and variable A antigen synthetic ability.
  
  
  CONCLUSIONS
  ABO genotyping can be a powerful asset in the transfusion service, but a thorough knowledge of the confounding factors that can lead to genotype/phenotype discrepancies is required.
authors.affiliation: The Institute for Transfusion Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA. myazer@itxm.org
authors.forename: Mark H
authors.initials: MH
authors.lastname: Yazer
authors.forename: Bahram
authors.initials: B
authors.lastname: Hosseini-Maaf
authors.forename: Martin L
authors.initials: ML
authors.lastname: Olsson
mesh_terms: D000017:ABO Blood-Group System / Q000235:genetics*; D000373:Agglutinins / Q000097:blood; D000483:Alleles; D001788:Blood Grouping and Crossmatching; D001803:Blood Transfusion / Q000379:methods*; D005838:Genotype; D006801:Humans; D010641:Phenotype
chemical_list: D000017:ABO Blood-Group System; D000373:Agglutinins