title: A Novel Variant B Allele of the ABO Blood Group Gene Associated with Lack of B Antigen Expression.
abstract: SUMMARY: BACKGROUND: The gene locus for the ABO blood group system encodes a glycosyltransferase. Alterations in the DNA sequence are associated with the blood groups and the expression levels of antigens on red blood cells. A number of ABO alleles have been described as the molecular basis of weak A or B antigens. PATIENTS AND METHODS: Here, we describe a novel variant B allele in a blood donor with discrepant results in routine forward (group A) and reverse (very weak anti-B isoagglutinins) ABO blood grouping. RESULTS: Determination of the ABO genotype using polymerase chain reaction-sequence-specific primers (PCR-SSP) indicated blood group A(2)B. Sequencing of the ABO gene exons 6 and 7 showed for 1 allele a G insertion into the GGGGGG sequence at position 811-816 of exon 7. The 816insG mutation (designated ABO*Bw20) led to a frame shift of the coding sequence and subsequent alteration of the protein sequence. The location of the mutation on a B allele was proven by PCR-SSP. Screening for the novel mutation in 211 blood donors with regular ABO phenotypes indicated that *Bw20 is a rare variant. CONCLUSIONS: The low levels of anti-B isoagglutinins associated with this novel variant indicate that residual undetectable amounts of B antigen may be present on red blood cells. The serological and molecular analysis of members of the blood donor's family further proved the phenotype-genotype correlation of the *Bw20 allele with antigen O and individually variable levels of anti-B isoagglutinins. The characterization of novel alleles associated with ABO subgroups may ensure the correct determination of blood groups in which serological methods are combined with molecular genetic approaches.
authors.affiliation: Institute of Transfusion Medicine and Immunology, University of Heidelberg, Medical Faculty of Mannheim, German Red Cross Blood Service of Baden-Württemberg - Hessen gGmbH, Mannheim, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Bugert
authors.forename: Erwin A
authors.initials: EA
authors.lastname: Scharberg
authors.forename: Karin
authors.initials: K
authors.lastname: Janetzko
authors.forename: Gabriele
authors.initials: G
authors.lastname: Rink
authors.forename: Kathrin
authors.initials: K
authors.lastname: Panter
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Richter
authors.forename: Harald
authors.initials: H
authors.lastname: Klüter