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Abstract
The B3 phenotype is the most common B subtype in Korea. The B305 allele (425 T>C, M142T) was first reported in 2 Chinese individuals; however, it has not yet been reported in the Koreans, and the impact of the M142T mutation on the expression of the B3 phenotype has also not been studied. To resolve an ABO discrepancy between a group O neonate and her group O father and A1B3 mother, blood samples from these individuals and other family members were referred to our laboratory for ABO gene analysis. The B305 allele was discovered in the neonate (B305/O01), her mother (A102/B305), and her maternal aunt (B305/O02), while her father was typed as O01/O02. Transient transfection experiments were performed in HeLa cells using the B305 allele synthesized by site-directed mutagenesis; flow cytometric analysis revealed that this transfect expressed 35.5% of the total B antigen produced by the B101 allele transfect. For comparison, Bx01 allele transfects were also created, and they expressed 11.4% of the total B antigen expressed on the surface of B101 transfects. These experiments demonstrate that the M142T (425 T>C) mutation is responsible for the B subtype phenotype produced by the B305 allele.
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Fig. 1.
The phenotype and ABO genotype of the family members included in this study. The arrow indicates the propositus, a 7-day-old neonate. NT=not available for testing.
Fig. 2.
The DNA sequence of the region around nucleotide 425 (arrow) in exon 7 of the ABO gene in the neonate's mother. The upper chromatogram demonstrates the heterozygous sequence (C and T) at nt. 425. The lower chromatogram demonstrates the nucleotide sequence of the region around nt. 425C in the setting of a B305 allele after cloning (B allele-specific polymorphisms are not shown; the A102 and B305 genes are otherwise identical in this area).
Fig. 3.
(A) Flow cytometric histogram demonstrating the population of green fluorescent protein (GFP)-positive transfected HeLa cells. (B) Representative histograms from each of the 3 B allele constructs expressed in HeLa cells, and the mock transfect used as a control. Note the absence of a mixed-field pattern in the B305 histogram and the weak expression of B antigen in the Bx01 histogram. The mean fluorescence intensity (MFI) for each transfect is shown in parentheses. (C) The amount of B antigen produced by each of the 2 B subtype transfects relative to that produced by the B101 transfect.
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