The Gm polymorphism and racial admixture in six Amazonian populations

Unveiling the Diversity of Immunoglobulin Heavy Constant Gamma (IGHG) Gene Segments in Brazilian Populations Reveals 28 Novel Alleles and Evidence of Gene Conversion and Natural Selection

Even though immunoglobulins are critical for immune responses and human survival, the diversity of the immunoglobulin heavy chain gene (IGH) is poorly known and mostly characterized only by serological methods. Moreover, this genomic region is not well-covered in genomic databases and genome-wide association studies due to particularities that impose technical difficulties for its analysis. Therefore, the IGH gene has never been systematically sequenced across populations. Here, we deliver an unprecedented and comprehensive characterization of the diversity of the IGHG1, IGHG2, and IGHG3 gene segments, which encode the constant region of the most abundant circulating immunoglobulins: IgG1, IgG2, and IgG3, respectively. We used Sanger sequencing to analyze 357 individuals from seven different Brazilian populations, including five Amerindian, one Japanese-descendant and one Euro-descendant population samples. We discovered 28 novel IGHG alleles and provided evidence that some of them may have been originated by gene conversion between common alleles of different gene segments. The rate of synonymous substitutions was significantly higher than the rate of the non-synonymous substitutions for IGHG1 and IGHG2 (p = 0.01 and 0.03, respectively), consistent with purifying selection. Fay and Wu's test showed significant negative values for most populations (p < 0.001), which indicates that positive selection in an adjacent position may be shaping IGHG variation by hitchhiking of variants in the vicinity, possibly the regions that encode the Ig variable regions. This study shows that the variation in the IGH gene is largely underestimated. Therefore, exploring its nucleotide diversity in populations may provide valuable information for comprehension of its evolution, its impact on diseases and vaccine research.

Isoelectric focusing studies in Brazilian Indians--uncovering variation of ORM, AHSG and IF

Allele frequencies for the orosomucoid 1 (ORM1), orosomucoid 2 (ORM2), alpha-2-HS-glycoprotein (AHSG) and complement component I (IF) loci were studied in 393 individuals of three Brazilian Indian tribes. In the ORM1 locus only two alleles were observed among the Urubu-Kaapor, while five were found among the Pacaás Novos. The frequency of ORM1*1 was similar in these two tribes (0.734 and 0.715, respectively) but departed more markedly among the Parakanã (0.870). Variation for ORM2 locus was found among the Pacaás Novos only, with ORM2*3 being observed in just three individuals. A new variant (AHSG*PN) was found in the AHSG system. Frequency for AHSG*1 was unexpectedly low in the three tribes, especially, among the Pacaás Novos, where the prevalence (0.145) is the lowest considering other data reported thus far. For IF locus, variability was also restricted to only one trible (Urubu-Kaapor) and attributed to a new polymorphic allele, IF* A3.

Genetic variation within the Tupi linguistic group: new data on three Amazonian tribes

A total of 505 individuals belonging to four populations of three Brazilian Indian tribes were variously studied in relation to 34 genetic systems, and the results were compared with South American Indian averages and five other Tupi populations. Rare variants (CdE of the Rh system, PGM211-1, Cp A-CAY1, serum cholinesterase2 C5+ and some Gm combinations) were observed with varying prevalences, and the three tribes showed different degrees of departure (28%-40% of differences of 10% or more in gene frequencies) from South American Indian averages. People from two communities who speak the same language and are labelled as belonging to the same tribe (Asurini) showed a large degree of genetic differentiation. Another of the tribes studied (Urubu-Kaapor) link through genetic distance analyses with two other tribes from the north of the continent, forming a distinct microevolutionary unit. These features emphasize the peculiarities of the genetic variation in populations with a hunter-gatherer, rudimentary agriculture type of economy.

A note on the presence of blood groups A and B in pre-Columbian South America

The results of ABO typing in Chilean mummies, a review of published South American paleoserological studies and a systematic discrepancy of admixture estimates based on ABO and Gm genes support the hypothesis that Andean pre-Columbian populations possessed the A (and perhaps the B) gene in small frequencies.

Gene flow across tribal barriers and its effect among the Amazonian Içana river Indians

Demographic information was obtained from 622 individuals of five communities of primarily Baniwa Amerindians living near the Içana river in Brazil. Four of these populations, plus another from the same area, were also studied genetically. The latter investigation included the blood and, in some cases, saliva of 531 subjects, variously tested in relation to 40 genetic systems. Demographically these groups are characterized by young age, high intertribal admixture, low non-Indian admixture, high exogamy but low marital distance and high inbreeding, high fertility but low variance in offspring number, and relatively low mortality. Their gene pool shows a peptidase B variant (PEPB2BAN1) and "private" polymorphism of carbonic anhydrase2 (CA2BAN1) until now observed only among them. Other distinctive characteristics are the low frequencies of LNS (0.08), LNs (0.09), RZ (0.01), RO or r(0.02), ACPA (0.08), GALTD (0.01), and the relatively high prevalences of Gm (0.05) and Gc1 (0.82). TfDchi occurs with a low prevalence (0.01). Genetic distance analysis reveals that the one Baniwa sample by history comprised of minimally admixed individuals is quite similar genetically to the Wapishana, another Arawak-speaking tribe some 900 km to the east, and that the genetic distances between the Baniwa communities reflect the amount of historical admixture in a way that indicates which should be excluded from considerations of intertribal genetic distances. Finally, the genetic relation of the Baniwa to the nearby tribes is examined.

Population structure and blood genetics of the Pacaás Novos Indians of Brazil

Two communities of relatively recently contacted Brazilian Indians, the Pacaás Novos, have been studied in relation to several demographic parameters and 28 genetic systems. The age and sex distribution, fertility and mortality patterns were not very distinct in the two populations, but they differed markedly in relation to the mating, migration and genetic data (six of the 19 variable loci showed differences higher than 10%). This was interpreted as being the consequence of a fission event, one of the many that may periodically occur, sometimes followed by fusions, in populations at this cultural level. The Pacaás Novos also show some distinctive features when previous genetic studies of South American Indians are reviewed, eight alleles of the variable 19 (LMS, R2, R0, Se, Hp1, Gm1,2;21, Gc1F and PGM1(1)), presenting differences varying between 12%-34% from the average obtained considering these earlier investigations.