title: An age-dependent ABO discrepancy between mother and baby reveals a novel A(weak) allele.
abstract: BACKGROUND
  Discrepancies in ABO grouping arise due to different reasons, posing a threat to patient safety. Underlying causes include mixed-field agglutination after transfusion, chimerism, fetomaternal exchange, or inheritance of unusual alleles resulting in weak A/B antigen expression. Cord blood from the infant of a group A2 B mother typed as group O, H+. Samples were investigated to elucidate this conundrum.
  
  
  METHODS
  Genomic DNA was analyzed by ABO genotyping and sequencing. Red blood cells (RBCs) were characterized by routine serology and flow cytometry. Glycosyltransferase structure was predicted with 3D-modeling software.
  
  
  RESULTS
  The mother genotyped as ABO*A1.01/B.01, and the baby, ABO*A1.01/O.01.01. Sequencing revealed a substitution, 311T>A, in the ABO*A1-like allele, which predicts Ile104Asn. Flow cytometry demonstrated A antigen on the mother's RBCs equivalent to the A2 phenotype while no A was detectable on cord RBCs. However, blood from the 11-month-old child demonstrated markedly increased A expression, likely reflecting initiation of carbohydrate chain branching.
  
  
  CONCLUSIONS
  We unraveled a novel A(weak) allele (ABO*AW.29) in a case of apparent nonmaternity. Residue 104 is far from the catalytic site and may be involved in stabilizing the glycosyltransferase by dimerization. Our data support that the group AB mother's B-transferase stabilizes the altered A-transferase by heterodimerization, exemplifying the allelic enhancement phenomenon.
authors.affiliation: Division of Hematology and Transfusion Medicine, Department of Laboratory Medicine, Lund University, Lund, Sweden; Clinical Immunology and Transfusion Medicine, Laboratory Medicine, Office of Medical Services, Lund, Sweden.
authors.forename: Jill R
authors.initials: JR
authors.lastname: Storry
authors.forename: Jennifer
authors.initials: J
authors.lastname: Condon
authors.forename: Annika K
authors.initials: AK
authors.lastname: Hult
authors.forename: Andrew
authors.initials: A
authors.lastname: Harrison
authors.forename: René
authors.initials: R
authors.lastname: Jørgensen
authors.forename: Martin L
authors.initials: ML
authors.lastname: Olsson
mesh_terms: D000017:ABO Blood-Group System / Q000097:blood / Q000235:genetics*; D000328:Adult; D000483:Alleles; D001483:Base Sequence; D004912:Erythrocytes / Q000378:metabolism; D005260:Female; D005838:Genotype; D006801:Humans; D007223:Infant; D008969:Molecular Sequence Data
chemical_list: D000017:ABO Blood-Group System