Histoblood Group A Variants, O Variants, and Their Alleles

Abstract

Histoblood group A phenotypes showing weaker agglutination, by anti-A antibodies or lectin (e.g., Dolichos biflorus), than regular A phenotypes (A₁ are called collectively “weak A,” and include A₂, A₃, A _x , A _m , A _el , etc. (Race and Sanger 1975). The A₂ phenotype is common in Caucasians (average incidence 10%–15%), and particularly in Scandinavians (up to 25%), and very rare in Asian populations (to date, only studied in Japanese). It is sometimes difficult to distinguish the A₂ from the O phenotype when A₂ agglutination by anti-A antibodies is very weak. A₃, A _x , A _m , and A _el are very rare, even in Caucasians. “Weak B” phenotypes are also very rare. B _x , which is comparable to A _x , is extremely rare in Caucasians, and slightly more common (but still rare) in Japanese (Yamaguchi et al. 1970). The presence of O variants has become clear since the O gene was sequenced, and the genetic structures of the variants have been elucidated (Olsson et al. 1998).