Heterogeneity in genetic admixture across different regions of Argentina.

The population of Argentina is the result of the intermixing between several groups, including Indigenous American, European and African populations. Despite the commonly held idea that the population of Argentina is of mostly European origin, multiple studies have shown that this process of admixture had an impact in the entire Argentine population. In the present study we characterized the distribution of Indigenous American, European and African ancestry among individuals from different regions of Argentina and evaluated the level of discrepancy between self-reported grandparental origin and genetic ancestry estimates. A set of 99 autosomal ancestry informative markers (AIMs) was genotyped in a sample of 441 Argentine individuals to estimate genetic ancestry. We used non-parametric tests to evaluate statistical significance. The average ancestry for the Argentine sample overall was 65% European (95%CI: 63-68%), 31% Indigenous American (28-33%) and 4% African (3-4%). We observed statistically significant differences in European ancestry across Argentine regions [Buenos Aires province (BA) 76%, 95%CI: 73-79%; Northeast (NEA) 54%, 95%CI: 49-58%; Northwest (NWA) 33%, 95%CI: 21-41%; South 54%, 95%CI: 49-59%; p<0.0001] as well as between the capital and immediate suburbs of Buenos Aires city compared to more distant suburbs [80% (95%CI: 75-86%) versus 68% (95%CI: 58-77%), p = 0.01]. European ancestry among individuals that declared all grandparents born in Europe was 91% (95%CI: 88-94%) compared to 54% (95%CI: 51-57%) among those with no European grandparents (p<0.001). Our results demonstrate the range of variation in genetic ancestry among Argentine individuals from different regions in the country, highlighting the importance of taking this variation into account in genetic association and admixture mapping studies in this population.

[Gene mixture in a population sample from Buenos Aires City]. / Mezcla genica en una muestra poblacional de la Ciudad de Buenos Aires.

The aim of this study is to estimate the gene admixture in the population of Buenos Aires City from samples of blood donors, which come from a public health centre (Hospital de Clínicas). These studies were performed on 218 unrelated people, who donated blood during the year 2002. Eight erythrocyte genetic systems and GM/KM allotypes were analysed. A survey to obtain information about place of birth, present residence and genealogical data of the donors was performed. The gene frequencies were determined using a method of maximum likelihood. The genetic admixture was calculated through the ADMIX program (trihibride). The Amerindian and African contributions were 15.8% and 4.3% respectively. These data were compared with those obtained in a previous study performed in a private centre (Hospital Italiano de Buenos Aires) and significant differences were observed, except in the KM system. The results obtained are in concordance with the demographic and historic information of Buenos Aires City.

Mezcla genica en una muestra poblacional de la ciudad de Buenos Aires / Gene mixture in a population sample from Buenos Aires City

Este estudio tiene como objetivo estimar la mezcla génica en la población de la Ciudad de BuenosAires, a partir de muestras de dadores de sangre provenientes de un centro público de salud (Hospitalde Clínicas). Los estudios se realizaron sobre 218 personas no emparentadas que donaron su sangre duranteel año 2002. Se analizaron 8 sistemas genéticos eritrocitarios y los alotipos GM/KM. Se realizó una encuestacon la finalidad de obtener información sobre lugar de nacimiento, residencia actual y datos genealógicosde los dadores. Las frecuencias génicas se determinaron empleando métodos de máxima verosimilitud. Paracalcular la mezcla génica se aplicó el programa ADMIX (trihíbrido). Se registró un 15.8% de aporte indígena(AI) y 4.3% de africano (AA). Estos datos se compararon con un estudio previo realizado en un centro privado(Hospital Italiano de Buenos Aires), no observándose diferencias significativas salvo en el sistema Km. Los resultadosobtenidos se corresponden con la información histórica y demográfica de la ciudad de Buenos Aires.

The aim of this study is to estimatethe gene admixture in the population of Buenos Aires City from samples of blood donors, whichcome from a public health centre (Hospital de Clínicas). These studies were performed on 218 unrelated people,who donated blood during the year 2002. Eight erythrocyte genetic systems and GM/KM allotypes were analysed.A survey to obtain information about place of birth, present residence and genealogical data of the donors wasperformed. The gene frequencies were determined using a method of maximum likelihood. The genetic admixturewas calculated through the ADMIX program (trihibride). The Amerindian and African contributions were 15.8%and 4.3% respectively. These data were compared with those obtained in a previous study performed in a privatecentre (Hospital Italiano de Buenos Aires) and significant differences were observed, except in the KM system.The results obtained are in concordance with the demographic and historic information of Buenos Aires City.

T-cell and chemokine receptor variation in south Amerindian populations.

The immune response of relatively small, endogamous populations is of special interest, because they may differ from those of large, ethnically diverse, urban groups. As a contribution to this area of investigation, we tested 99 individuals from two Brazilian native populations for two T-cell receptor gene segments (TCRBV3S1 and TCRBV18) and 241 subjects from eight tribes of this ethnic group in relation to the chemokine receptor CCR5delta32 allele. Differences in TCRBV3S1 and TCRBV18 prevalences of the Amerindians in relation to European- and African-derived individuals were not marked. We confirmed the absence of the CCR5delta32 allele in most groups, its presence in the Mura and Kaingang, probably because of European gene introgression.

African ancestry of the population of Buenos Aires.

The population of Argentina today does not have a "visible" black African component. However, censuses conducted during most of the 19th century registered up to 30% of individuals of African origin living in Buenos Aires city. What has happened to this African influence? Have all individuals of African origin died, as lay people believe? Or is it possible that admixture with the European immigrants made the African influence "invisible?" We investigated the African contribution to the genetic pool of the population of Buenos Aires, Argentina, typing 12 unlinked autosomal DNA markers in a sample of 90 individuals. The results of this analysis suggest that 2.2% (SEM=0.9%) of the genetic ancestry of the Buenos Aires population is derived from Africa. Our analysis of individual admixture shows that those alleles that have a high frequency in populations of African origin tend to concentrate among 8 individuals in our sample. Therefore, although the admixture estimate is relatively low, the actual proportion of individuals with at least some African influence is approximately 10%. The evidence we are presenting of African ancestry is consistent with the known historical events that led to the drastic reduction of the Afro-Argentine population during the second half of the 19th century. However, as our results suggest, this reduction did not mean a total disappearance of African genes from the genetic pool of the Buenos Aires population.

Genetic variability in Amerindian populations of Northern Argentina

The allelic variability of four dinucleotide microsatellites located in the HLA region (MOGc, D6S265, MIB, and TNFa) was analyzed in 67 individuals representing three Amerindian populations of the Argentine Gran Chaco: Toba, Wichi and Chorote. Genomic DNA was prepared from peripheral blood and DNA was extracted using the standard phenol-chloroform procedure. Alleles were identified by PCR, using an end-labelled reverse oligonucleotide primer (fluorescent 6 - Fam labeling). Despite the low number of samples studied, a high level of gene diversity was observed in each population and for each locus. Moreover, the mean number of alleles was 7.7, 5.3, 10.0, and 7.0 at loci MOGc, D6S265, MIB and TNFa, respectively. Differentiation tests between pairs of populations showed a clear differentiation between the Wichi and the other two groups. However, the proportion of the total genetic variability that is due to differences among populations, estimated by the Gst' index, was relatively low (6 percent). Almost all the genetic variation occurred at the intra-population level (96 percent). The high intra-populational genetic variation suggests the existence of an intensive gene flow among the Gran Chaco tribes. Historical information seems to confirm this result.

Demography, genetic diversity, and population relationships among Argentinean Mapuche Indians

Dados relativos a fertilidade, mortalidade e migraçäo de quatro comunidades de índios Mapuche localizadas em uma área linear na direçäo nordeste-sudoeste com 215 km de extensäo na Província de Rio Negro, Argentina, foram associados com a informaçäo genética fornecida por nove sistemas de grupos sangüíneos e os haplogrupos do DNA mitocondrial. Ambos os tipos de informaçäo apontam claramente para uma dicotomia, as quatro populaçöes sendo divididas em grupos de duas. O principal fator responsável por esta separaçäo é provavelmente graus diferentes de mistura com näo-índios. A variabilidade genética total foi muito similar em todos os grupos, aquela entre populações sendo de apenas 10 por cento deste valor. Foi confirmada a baixa prevalência do antígeno Diego(a) entre os Mapuche. O fato de que heterogeneidade genética significativa e conjuntos populacionais diversos foram observados em uma regiäo territorial täo pequena demonstra a sensibilidade dos enfoques demográfico e genético no esclarecimento da história humana.

Beta-globin gene cluster haplotypes in the Mapuche Indians of Argentina

Haplótipos derivados de cinco sítios de restriçäo polimórficos presentes no agrupamento da globina beta foram investigados em 86 cromossomos da populaçäo Mapuche da Argentina. Esses resultados foram analisados em conjunto com os previamente obtidos para dez tribos indígenas brasileiras. Oito haplótipos foram identificados, dos quais os mais freqüêntes foram o 2 (57 por cento) e o 6 (27 por cento). A presença do haplótipo 3 em 2 por cento dos cromossomos dos Mapuches é uma evidência de mistura com indivíduos de ancestralidade africana. Devido ao alto número de haplótipos, a heterozigosidade medida pelo índice Gini-Simpson é mais alta nos Mapuches do que nos índios brasileiros. A distribuçäo haplotípica nos Mapuches é também significativamente diferente da observada nas tribos brasileiras. Essa heterogeneidade poderia ser parcialmente explicada pela mistura com populaçöes näo-indígenas.

Crecimiento en escolares de Villa IAPI (Quilmes, Buenos Aires, Argentina) / Growth in school children of Villa IAPI (Quilmes, Buenos Aires, Argentina)

Growth in schoolchildren of Villa IAPI--a poor neighborhood placed near Buenos Aires (Argentina)--were cross-sectionally studied. Six hundred and forty five--291 males and 354 females--children from six to twelve years old were weighed (W), and the standing (StH) and sitting (SiH) heights, the head (HC) and the arm (AC) circumferences, and the triceps (TS) an the subscapular (SS) skinfolds were measured. The muscular braquial circumference (MC), and the length of the inferior segment of the body (IS) were also calculated. All of the measurements were transformed to "z" scores. It was observed that in all cases--except for 11 year-old females--both W and StH were diminished. This trend was stronger in males than in females. Both SiH an HC did not show differences with respect to local growth standards. Skinfold values however, were always greater in Villa IAPI children--except SS in 9 to 12 year-old males, and in 12 year-old females--than those of normal standards, Such differential growth pattern suggests that two joined strategies--for protection and adaption to unbalanced environment--actually acted in the Villa IAPI population.