title: A novel cis AB allele derived from a B allele through a single point mutation.
abstract: BACKGROUND
  The very rare cis AB phenotype, first described in 1964, corresponds to a special ABO allele encoding a glycosyltransferase that is capable of synthesizing both A and B substances. Until now, gene sequences of only two cis AB alleles were partially characterized. One involved the A1*02 allele with a single nonsynonymous substitution at codon 268, whereas the second arose from a single nonsynonymous substitution at codon 266 in exon 7 of a B1*01 allele.
  
  
  METHODS
  A cis AB phenotype was identified in a French family. The serologic characteristics of this phenotype were determined. The cis AB allele was characterized from exon 6 to exon 7 by cloning and sequencing.
  
  
  RESULTS
  The cis AB.tlse(*)01 allele is identical to B(1*)01 except for a single point mutation at nucleotide position 700, where a T replaces a C, implying a change of amino acid 234 (the B(1*)01 proline being replaced by a serine).
  
  
  CONCLUSIONS
  The cis AB.tlse(*)01 allele clearly differs from all previously reported ABO, including the two previous cis AB described.
authors.affiliation: Department of Immunohematology, French National Blood Service, Pyrénées Méditerranée, Toulouse, France.
authors.forename: Francis
authors.initials: F
authors.lastname: Roubinet
authors.forename: Daniel
authors.initials: D
authors.lastname: Janvier
authors.forename: Antoine
authors.initials: A
authors.lastname: Blancher
mesh_terms: D000017:ABO Blood-Group System / Q000235:genetics*; D000483:Alleles; D001788:Blood Grouping and Crossmatching; D003001:Cloning, Molecular; D005091:Exons; D005260:Female; D005602:France; D005700:Galactosyltransferases / Q000235:genetics*; D005838:Genotype; D016695:Glycosyltransferases / Q000378:metabolism; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D010375:Pedigree; D010641:Phenotype; D017354:Point Mutation; D017422:Sequence Analysis, DNA
chemical_list: D000017:ABO Blood-Group System; D016695:Glycosyltransferases; D005700:Galactosyltransferases; C023155:blood-group-substance alpha-D-galactosyltransferase