Molecular analysis of HLA class I alleles in the Mexican Seri Indians: implications for their origin

The molecular analysis of HLA class I loci has demonstrated that, although, the genetic profile is restricted in Amerindians, several micropolymorphis ms may be important in conferring a biological advantage. We analyzed the H LA-A and B genetic profile of Seris, a Mexican Indian tribe living in north western Mexico in the state of Sonora. There are presently only 619 individ uals. Our study included 100 Seris belonging to nine families. HLA-A and -B loci typing was performed by polymerase chain reaction using an amplificat ion refractory mutation system (PCR-ARMS) on a select group of samples; all of them were typed by polymerase chain reaction using sequence-specific ol iogonuoleotide probes (PCR-SSOP) at a low-intermediate resolution level. Th e correlation between the techniques was 100%. Only five HLA-A alleles and seven HLA-B alleles were found. A*0201, A*68, A*31, A*24, B*3501, B*40, B*5 1, B*3512 and B*15 were present in over 5% of the individuals. B*27052 was detected in 2%, B27 is absent in any other Mexican Indian groups previously studied. The presence of B27 may be the result of a founder effect due to different waves of southward migrations. The B-locus is more diverse and th e prevalent haplotypes were: A*0201-B*3501, A*0201-B*40, A*0201-B*3512, A*3 1-B*51, A*68-B*3501 and A*68-B*40. This genetic profile is different from t he pattern of other Mexicans. The phylogenetic tree suggests that Seris are more closely related to the Warao Indians from Venezuela, who live in a si milar ecosystem, and to some groups of Argentina, than they are to the Mexi can Lacandones who live in the jungle. These data emphasize the relevance o f the interaction between genes and environment.