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STUDY: The ABO blood group gene: A locus of considerable genetic diversity.
JOURNAL: Transfus Med Rev 2001 Jul;15(3):177-200
AUTHORS: Chester MA, Olsson ML.
ABSTRACT: The blood group ABO gene shows considerable polymorphism in most of the 7 exons. Introns examined so far have also shown blood group-related polymorphisms, as has an upstream enhancer region. Several polymorphisms affect the specificity of the gene product (glycosyltransferase) and explain the occurrence of blood group A and B. Other mutations are presumed to alter the activity rather than the specificity of the enzyme and result in weaker A and B blood group phenotypes. In total, 27 A alleles, 15 B alleles, 26 O alleles, and 4 AB hybrid alleles are described and surely more will surface in the near future. Variation in geographic/ethnic distribution of allele frequencies is discussed, along with the confusing nomenclatures currently in use.
COMMENTARY: Just looking at the total number of potential alleles shows that the ABO gene locus (on chromosome 9) is the site of considerable variation. The genetic links beteween blood type are not commonly recognized in evaluating the blood type diet theory, but probably are the main reason biological values, such as stomach acid or intestinal enzyme levels, are known to value by ABO type.
The variations in geographic and ethnic distribution serve to support the premise than major variation in blood group gene distribution are the result of biological, environmental or climatic changes.