A family exhibiting the CIS—AB genotype

First report of Cis-AB inheritance from North India

“…The results showed the absence of A and markedly increased levels of B and H substances in all the cis cases and only H in mother. Whereas most of the earlier reported cases had normal levels of A and H and reduced levels of B substance (Seyfried et al, 1964, Madsen et al 1968, Pacuszka et al 1975, whereas only B substance was observed in some other case (Reviron et al 1968, Ford et al, 1989, Lopez 1976, Pacuszka et al 1975.…”

“…the presence of weak A (1:1) and B antigens (1:16) where as those with genotype A1/A2B~ (III-1, 3 and 5) showed weak agglutination only with anti-B antisera. Ford et al (1989) reactions were observed with seven antisera which may not be potent enough. Many cases of cis AB may have gone unnoticed because of it, leading to either sporadic reports or low incidence of cis AB in the various populations all over the world.…”

A novel cis AB allele derived from a B allele through a single point mutation

“…Individuals with the cis AB phenotype are characterized by a nonclassic mode of inheritance of A and B antigens expressed at the membrane of RBCs: A and B are not transmitted as two independent alleles but as a single allele, referred to as “cis AB . ” The incidence of the cis AB phenotype is very low and, since the first two reports, this phenotype has been recorded in only a few well‐documented family studies 4‐16 . Even in the Japanese population, in which the cis AB frequency was reported to be higher than in whites, it is very low (1.1 × 10 −5 ) 17 .…”