title: Genetic and mechanistic evaluation for the mixed-field agglutination in B3 blood type with IVS3+5G>A ABO gene mutation.
abstract: BACKGROUND
  The ABO blood type B(3) is the most common B subtype in the Chinese population with a frequency of 1/900. Although IVS3+5G>A (rs55852701) mutation of B gene has been shown to associate with the development of B(3) blood type, genetic and mechanistic evaluation for the unique mixed-field agglutination phenotype has not yet been completely addressed.
  
  
  RESULTS
  In this study, we analyzed 16 cases of confirmed B(3) individuals and found that IVS3+5G>A attributes to all cases of B(3). RT-PCR analyses revealed the presence of at least 7 types of aberrant B(3) splicing transcripts with most of the transcripts causing early termination and producing non-functional protein during translation. The splicing transcript without exon 3 that was predicted to generate functional B(3) glycosyltransferase lacking 19 amino acids at the N-terminal segment constituted only 0.9% of the splicing transcripts. Expression of the B(3) cDNA with exon 3 deletion in the K562 erythroleukemia cells revealed that the B(3) glycosyltransferase had only 40% of B(1) activity in converting H antigen to B antigen. Notably, the typical mixed-field agglutination of B(3)-RBCs can be mimicked by adding anti-B antibody to the K562-B(3) cells.
  
  
  CONCLUSIONS
  This study thereby demonstrates that both aberrant splicing of B transcripts and the reduced B(3) glycosyltransferase activity contribute to weak B expression and the mixed-field agglutination of B(3), adding to the complexity for the regulatory mechanisms of ABO gene expression.
authors.affiliation: Department of Laboratory Medicine, Chang-Gung Memorial Hospital, Taoyuan County, Taiwan.
authors.forename: Ding-Ping
authors.initials: DP
authors.lastname: Chen
authors.forename: Ching-Ping
authors.initials: CP
authors.lastname: Tseng
authors.forename: Wei-Ting
authors.initials: WT
authors.lastname: Wang
authors.forename: Chien-Feng
authors.initials: CF
authors.lastname: Sun
mesh_terms: D000017:ABO Blood-Group System / Q000235:genetics*; D000372:Agglutination Tests; D017398:Alternative Splicing / Q000235:genetics*; D044466:Asian People / Q000235:genetics*; D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers / Q000235:genetics; D005434:Flow Cytometry; D016695:Glycosyltransferases / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D018709:Statistics, Nonparametric; D013624:Taiwan
chemical_list: D000017:ABO Blood-Group System; D017931:DNA Primers; D016695:Glycosyltransferases