Identification of a novel A2 allele through nt543 substitution

• Main Authors: Ying-Hao Wen, Tzong-Shi Chiueh, Wei-Ting Wang, Wei-Tzu Lin, Ding-Ping Chen
• Format: Article
• Language: English
• Published: Elsevier 2020-04-01
• Series: Journal of the Formosan Medical Association
• Online Access: http://www.sciencedirect.com/science/article/pii/S0929664619302888

Background: ABO blood system has many subgroups. In A group, A1 phenotype and A2 phenotype are more common, and A2 is caused by deletion or substitution in A1 allele (ABO*A1.01). Methods: Based on standard ABO serological test, the subject was identified as A2 phenotype. Direct sequencing and ABO gene cloning were performed to analyze the allele. Results: The subject had one A1v allele (ABO*A1.02) and one O allele. The haplotype sequencing analysis of each allelic clone demonstrated that allele 1 was A1v (ABO*A1.02) allele with nt543 variation (543 G > C) and allele 2 was O1v allele (ABO*O.01.02) with nt261 deletion and nt220 variation. Conclusion: The 543 G > C nucleotide substitution of the present A1v allele (ABO*A1.02) shares the same sequence variation site with Ax allele (ABO*AW.33) (543 G > T), and both 543 G > C and 543 G > T nucleotide substitutions encode the same amino acid change of tryptophan to cysteine. Mechanism, such as allelic enhancement, has been proposed to explain this controversial phenotype–genotype relationship. But in present case, there has been no B allele to enhance the expression of Ax to that expected of A2, so there could be another novel underlying mechanism to be investigated. Keywords: A2 phenotype, Blood group, 543 G>C, A1v (ABO*A1.02) allele