In the century since the discovery of the ABO blood groups, numerous associations between ABO groups and disease have been noted. However, the selection pressures defining the ABO distributions remain uncertain. We review published information on Plasmodium falciparum infection and ABO blood groups. DNA sequence information dates the emergence and development of the group O allele to a period of evolution before human migration out of Africa, concomitant with P falciparum's activity. The current geographic distribution of group O is also consistent with a selection pressure by P falciparum in favor of group O individuals in malaria-endemic regions. We critically review clinical reports of ABO and P falciparum infection, documenting a correlation between disease severity and ABO group. Finally, we review published data on the pathogenesis of P falciparum infection, and propose a biologic model to summarize the role of ABO blood groups in cytoadherence biology. Such ABO-related mechanisms also point to a new hypothesis to account for selection of the Le(a؊b؊) phenotype. Taken together, a broad range of available evidence suggests that the origin, distribution, and relative proportion of ABO blood groups in humans may have been directly influenced by selective genetic pressure from P falciparum infection.
IntroductionThe ABO blood group system is arguably the best known, and yet the most functionally mysterious, genetic polymorphism in humans. In clinical practice, ABO is the most important system for blood group compatibility. In the century since their discovery, ABO antigen associations with infections and other diseases have been the subject of hundreds of publications. 1,2 Some reports found unexpected associations, such as the susceptibility of group A individuals to salivary or gastric cancers. 3 However, associations with diseases affecting humans after reproduction are not expected to exert any genetic selection. Thus, despite a large body of literature, the evolutionary basis for the origin and diversity of ABO blood group antigens remains uncertain. Much new information has emerged since a relationship between ABO and malaria was first suggested more than 40 years ago. 4 We review literature in support of the hypothesis that Plasmodium falciparum malaria has shaped the distribution of ABO blood groups in humans. 5 We offer 4 arguments in support of this hypothesis. First, we review evidence that P falciparum was present at the time when ABO polymorphisms arose. Second, we note that the current worldwide distribution of ABO groups is consistent with an effect from P falciparum. Third, we critically review studies examining clinical outcomes during P falciparum infection. Fourth, we offer proposed biologic mechanisms relating host ABO group to the pathophysiology and lethality of P falciparum malaria. P falciparum: the strongest force in the recent history of the human genome P falciparum has been called "the strongest known force for evolutionary selection in the recent history of the human genome." 6 Th...