Determination of ABO glycosyltransferase genotypes by use of polymerase chain reaction and restriction enzymes

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Abstract
BACKGROUND: The molecular basis of red cell ABO group antigens has been determined. The genes encoding the group A and B glycosyltransferases and a nonfunctional group O transferase have been cloned and sequenced. All three genes were similar. When compared to the nucleotide sequence of the A gene, the O gene has a one-base deletion that leads to a frame shift and results in a nonfunctional protein. The B gene differs from the A gene at seven nucleotides. STUDY DESIGN AND METHODS: Techniques using polymerase chain reaction and restriction enzymes to determine ABO transferase genotypes from white cell DNA were modified. Nucleotide sequence differences within the genes were analyzed by the application of selected restriction enzymes. Restriction enzymes Asp718 and BstEII were used to analyze the genes at nucleotide 258, and BssHII and Kas I were used to analyze the genes at nucleotide 523. ABO red cell phenotypes were compared in 60 unrelated individuals with ABO transferase genotypes. The ABO phenotypes and genotypes of individuals from two different families were also analyzed to determine if this method could distinguish individuals who were homozygous for A or B transferase genes from those who were heterozygous. RESULTS: The phenotypes and genotypes were consistent for all unrelated individuals, and within the families, heterozygous individuals could be distinguished from homozygous individuals. Nevertheless, two individuals from one family were found to have a group A red cell phenotype, but when the transferase genes were analyzed at nucleotide 523 with enzymes BssHII and Kas I, both A and B transferase genes were detected. Further analysis of the transferase genes at nucleotide 700 by using restriction enzymes Alu I and Hpa II and those at nucleotide 793 by using enzyme BstNI found that both transferase genes in the two individuals were similar to the A transferase gene. CONCLUSION: An A allele of the group A glycosyltransferase was detected that had the same sequence as the B gene at nucleotide 523 but was identical to the A gene at positions 700 and 793. The identification of this variant gene makes genotyping at nucleotide 523 unreliable. However, analysis of the genes at other sites of nucleotide variation may accurately identify phenotypes.