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A clue to the basis of allelic enhancement: occurrence of the A x subgroup in the offspring of blood group O parents
Author(s) -
Olsson M. L.,
Michalewska B.,
Hellberg Å.,
Walaszczyk A.,
Chester M. A.
Publication year - 2005
Publication title -
transfusion medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.471
H-Index - 59
eISSN - 1365-3148
pISSN - 0958-7578
DOI - 10.1111/j.1365-3148.2005.00603.x
Subject(s) - allele , abo blood group system , biology , genotyping , genetics , genotype , locus (genetics) , microbiology and biotechnology , antigen , mendelian inheritance , gene
summary . Apparent deviation from Mendelian rules of blood group inheritance is rarely observed. Blood group O parents with children expressing weak A subgroups have occasionally been described but not explained. A detailed serological investigation of such a family is described here. The ABO locus was analysed by PCR‐ASP/restriction fragment length polymorphism genotyping and DNA sequencing. The propositus' RBCs were very weakly agglutinated with monoclonal anti‐A but distinctly with polyclonal anti‐A,B, i.e. typical for A x . Serum anti‐A 1 (titre 4) and ‐B were present. Her parents' blood groups were both clearly O, with titres of serum anti‐A 1 , and ‐A at 16 and 4, respectively. Adsorption/ elution studies demonstrated A antigen on the daughter's cells only. The ABO genotypes were: mother, A x O 1 ; father, O 1v O 2 ; and propositus, A x O 2 . The A x allele was an A 1 ‐O 1v hybrid allele with a crossing‐over breakpoint between positions 235 and 446 in intron 6 ( A x ‐4). Compared to the A 1 glycosyltransferase, this allele predicts a protein with two amino acid substitutions (Phe216Ile and Met277Val) known to yield either weakly expressed or no A antigen on RBCs. This study suggests that the nature of the ABO allele in trans can influence A antigen expression, a phenomenon previously described as allelic enhancement (or reinforcement). Potential mechanisms for this are discussed.