A Case of A_x Phenotype Transmitted by an A₂B Parent

Abstract

The authors report a family in which the father is Ax, the mother B, the paternal grandmother Ax; 3 children out of 6 are A2B and the other three Ax. One of A2B children is married to an O subject, and she had a son of phenotype Ax. It was observed that Ax gene in position trans of a B gene behaves phenotypically as an A2.

Three missense mutations, including a novel 860C>T transition, and allelic enhancement phenomenon associated with ABO blood subgroups A in Taiwan

“…Moreover, analyses of Family C showed that this A x (860C>T) allele expressed as phenotype A 3 B in the A x / B101 heterozygote, but as phenotype A x in the A x / O01 heterozygote. This phenomenon was similar to the finding in a French family that an A gene expressed as A x in A / O members, but as A 2 in A/B members 20 . This phenomenon could probably be the reason for serologic discrepancy between parents and children.…”

A clue to the basis of allelic enhancement: occurrence of the Ax subgroup in the offspring of blood group O parents

“…On the basis of the current case study, the concept of allelic enhancement could be correlated to the presence of O 2 , but not the O 1 allele, in trans , an idea also supported by other pedigrees curiously involving the A x and O 2 alleles (Olsson & Chester, 1998), otherwise rarely or infrequently found in the populations studied, respectively. Yet other studies have suggested that the B allele in trans position may be involved (Ducos et al ., 1975; Salmon & Cartron, 1976; Olsson & Chester, 1998). In this context, it is interesting to note the similarities between O 2 and B alleles, mainly in exon 6, intron 6 and exon 7 (Olsson & Chester, 1998; Irshaid et al ., 1999).…”

The genetic and phenotypic basis of blood group A subtypes in Koreans

“…From the family study, we observed allelic enhancement of the A var allele, which is an enhancement of the phenotypic expression of subtype A or B genes in A / B heterozygotes. In a French family, an A gene was expressed as A x in A/O members, but as A 2 in A/B members (Ducos et al ., 1975). In a Swedish family, an ABO allele with the A 2 sequence in exons 6 and 7 was expressed as A 2 in the A 2 /B mother, but as A x in her A/O 1v children and grandchildren (Olsson & Chester, 1998).…”