MICA polymorphism in South American Indians

We have studied the MICA alleles of 196 unrelated subjects from three South American Indian tribes (Toba, Wichi and Terena). They are members of isolated tribes located in the Gran Chaco area in northeastern Argentina and in Mato Grosso do Sul in South Central Brazil. Of 55 previously known alleles, nine were observed in South American Indians, compared with 16 that were found in North American Caucasians, suggesting a more restricted allelic distribution of MICA in these tribes. In South American Indians, MICA *00201 was the most frequent allele, with a gene frequency of 33% in Toba, 47% in Wichi and 44% in Terena. MICA *00201, MICA *027 (external domain sequence like MICA *008/TM allele A5) and MICA *010 accounted for more than 90% of all the MICA genes in South American Indians. In North American Caucasians, MICA *00801 (*008/A5.1) accounted for 42% of the genes and was the most common allele. We observed a high degree of linkage disequilibrium between certain alleles of MICA and of HLA-B in the South American Indian populations. Phylogenetic trees constructed using gene frequencies of the transmembrane short tandem repeats in the populations reported here, and in other populations taken from published reports, suggest that South American Indians are more closely related to Asians than to Europeans.