HLA class II diversity in seven Amerindian populations. Clues about the origins of the Aché.

The study of the HLA variability of Native American populations revealed several alleles specific to one or more of the Latin American indigenous populations. The analysis of Amerindian groups distributed all over the continent might inform about the area of origin and the dispersal of these alleles and shed light on the evolution of this remarkable polymorphism. Moreover, HLA alleles and haplotypes are excellent markers to understand the genetic relationships between populations. For these reasons, we characterized the HLA class II polymorphism in seven South American Amerindian populations and compared the results with those previously reported for other Amerindian groups. The Guarani-Kaiowá (n = 160) and Guarani-Nandeva (n = 87) were from the Brazilian state of Mato Grosso do Sul, the Guarani-M'byá (n = 93) and Kaingang (n = 235) from Paraná state, the Aché (n = 89) from eastern Paraguay, the Quechua (n = 44) from Andean Peru. From Amazonia, a heterogeneous group was analyzed (n = 45). The most frequent alleles and haplotypes are common also in other Amerindian populations. Each HLA-DRB1 allele was typically found in combination with just one DQA1-DQB1 haplotype, most likely as a result of some form of random genetic drift and reduced gene flow from non-Amerindians. The frequency distribution differed significantly among all populations, although differences were less pronounced between the Guarani subgroups. Marker alleles allowed an estimate of European and sub-Saharan African gene flow into these populations: Quechua 23%, Guarani-Nandeva 14%, Kaingang 7%, Guarani-M'byá 4%, Guarani-Kaiowá, Amazonia, and Aché 0%. Interestingly, the DRB1*1413 allele, previously found only among the Guarani-M'byá (frequency 15%), appeared in the Aché (8%). The relationship of the Aché to other Amerindian populations is unclear, and this finding reveals a link with the Guarani. On the basis of genetic distance and the HLA allele/haplotype set, we propose that the Aché are differentiated Tupi-Guarani group, most closely related to the Guarani-M'byá.

Genetic diversity in an Andean population from Peru and regional migration patterns of Amerindians in South America: data from Y chromosome and mitochondrial DNA.

The genetic variability of a Quechua-speaking Andean population from Peru was examined on the basis of four Y chromosome markers and restriction sites that define the Amerindian mitochondrial DNA (mtDNA) haplogroups. Forty-nine out of 52 (90.4%) individuals had mtDNA which belonged to one of the four common Amerindian haplogroups, with 54% of the samples belonging to haplogroup B. Among 25 males, 12 had an Amerindian Y chromosome, which exists as four haplotypes defined on the basis of the DYS287, DYS199, DYS392 and DYS19 markers, three of which are shared by Amazonian Amerindians. Thus, there is a clear directionality of marriages, with an estimated genetic admixture with non-Amerindians that is 9 times lower for mtDNA than for Y chromosome DNA. The comparison of mtDNA of Andean Amerindians with that of people from other regions of South America in a total of 1,086 individuals demonstrates a geographical pattern, with a decreasing frequency of A and C haplotypes and increasing frequency of the D haplotype from the north of the Amazon River to the south of the Amazon River, reaching the lowest and the highest frequencies, respectively, in the more southern populations of Chile and Argentina. Conversely, the highest and lowest frequencies of the haplogroup B are found, respectively, in the Andean and the North Amazon regions, and it is absent from some southern populations, suggesting that haplotypes A, C and D, and haplotype B may have been dispersed by two different migratory routes within the continent.

Ethnic heterogeneity of the factor XIII Val34Leu polymorphism.

A polymorphism in the coagulation factor XIII gene (FXIII Val34Leu) has been recently described to confer protection for arterial and venous thrombosis and to predispose to intracerebral hemorrhage. At present it is known that FXIII Val34Leu is prevalent in Caucasians, but information upon its distribution in different ethnic groups is scarce. We investigated the prevalence of FXIIIVal34Leu in 450 unrelated subjects of four ethnic groups: 97 Caucasians (Brazilians of European descent and Portuguese), 149 Blacks (Brazilians, and Africans from Cameroon, Zaire and Angola), 40 Asians (Japanese descendents) and 164 Amerindians from South America. PCR amplification of exon 2 of FXIII gene followed by MseI restriction-digestion was employed to define the genotypes. FXIIIVal34Leu was detected in 44.3% of the Caucasians, in 28.9% of the Blacks, in 2.5% of the Asians and in 51.2% of the Amerindians. These data confirm that FXIII Val34Leu is highly prevalent in Caucasians and indicate that it is rarer in populations of African origin. The very high frequency among Amerindians indicates that FXIII Val34Leu is not absent among Asians, and since it has a very low prevalence in Japanese, a heterogeneity in its distribution in Asia may be inferred. Taken together, our data showed that FXIII Val34Leu exhibits a significant ethnic heterogeneity, a finding that is relevant for studies relating this polymorphism with thrombotic and bleeding disorders.

Diversity of the human Y chromosome of South American Amerindians: a comparison with blacks, whites, and Japanese from Brazil.

We defined the Y-chromosome haplotypes on the basis of six polymorphic sites: an Alu-element insertion (YAP), a single-base change (C-->T at DYS199), one trinucleotide repeat (DYS392) and three tetranucleotide repeats (DYS393, DYS390 and DYS19). Among 140 Y chromosomes from Whites, Blacks, Japanese and Amerindians we identified 67 different haplotypes, the majority of them population-specific; only seven haplotypes were shared by three different racial groups, mostly owing to admixture. Overall, three main lineages can be defined on the basis of the YAP/DYS199/DYS392 markers: (a) a predominant /-/C/10/13/22 (or) 23/ lineage, observed among all racial groups; (b) a/+/C/ lineage which predominates among Blacks (comprising mainly the sublineage /+/C/10/13/), although it is eventually found among Japanese and Whites; and (c) a /-/T/ lineage observed only among Amerindians (comprising mainly the sublineage /-/T/13/13/). The decreasing haplotype diversity of the three lineages agrees with the idea that the first is the most ancient, while the last is the more recent. The data also indicate that the YAP insertion occurred in a /-/C/10/13/ chromosome and the C-->T mutation occurred in a /-/C/13/13/ chromosome. Finally, the data suggest that at least two Y-chromosome lineages (/-/C/13/ and /-/T/13/) contributed to the early peopling of the Americas, and supports the hypothesis that /-/T/13/ could be derived from /-/C/13/ and that both haplotypes could be present in the ancestral populations that peopled the continent.