Diversity in human MHC genes among ethnic groups worldwide

Human major histocompatibility complex (MHC) genes comprise multigene families, and several of them show extensive genetic polymorphisms in any ethnic group examined. Because MHC genotypes specify the immune- responsiveness of individuals, the variation in these genes among ethnic groups is directly related to ethnic differences of susceptibility to various diseases, including cancers. We have been studying the genetic variation in MHC genes to elucidate the relationship between genetic background of the ethnic groups and a variety of diseases. We have constructed the MHC database which contains MHC types from more than 27,000 individuals, and estimated the frequencies of MHC alleles and haplotypes for more than 80 ethnic groups of the world. In this paper, we focus on the genetic variation in human MHC genes, and provide some typical examples of how MHC alleles and haplotypes are distributed. We further show an evolutionary tree of 16 ethnic groups based on the allele frequencies of MHC genes. Such an approach toward the genetic diversity in human MHC genes provides not only useful information on the genetic background of different ethnic groups, but also basic knowledge for ethnoepidemiological studies on cancers and other important diseases.