Gian Franco De Stefano

Genetic Differentiation in South Amerindians Is Related to Environmental and Cultural Diversity: Evidence from the Y Chromosome

The geographic structure of Y-chromosome variability has been analyzed in native populations of South America, through use of the high-frequency Native American haplogroup defined by the DYS199-T allele and six Y-chromosome-linked microsatellites (DYS19, DYS389A, DYS389B, DYS390, DYS391, and DYS393), analyzed in 236 individuals. The following pattern of within- and among-population variability emerges from the analysis of microsatellite data: (1) the Andean populations exhibit significantly higher levels of within-population variability than do the eastern populations of South America; (2) the spatial-autocorrelation analysis suggests a significant geographic structure of Y-chromosome genetic variability in South America, although a typical evolutionary pattern could not be categorically identified; and (3) genetic-distance analyses and the analysis of molecular variance suggest greater homogeneity between Andean populations than between non-Andean ones. On the basis of these results, we propose a model for the evolution of the male lineages of South Amerindians that involves differential patterns of genetic drift and gene flow. In the western part of the continent, which is associated with the Andean area, populations have relatively large effective sizes and gene-flow levels among them, which has created a trend toward homogenization of the gene pool. On the other hand, eastern populations-settled in the Amazonian region, the central Brazilian plateau, and the Chaco region-have exhibited higher rates of genetic drift and lower levels of gene flow, with a resulting trend toward genetic differentiation. This model is consistent with the linguistic and cultural diversity of South Amerindians, the environmental heterogeneity of the continent, and the available paleoecological data.

Genetic variability of glutathione S-transferase enzymes in human populations: Functional inter-ethnic differences in detoxification systems

Glutathione S-Transferase enzymes (GSTs) constitute the principal Phase II superfamily which plays a key role in cellular detoxification and in other biological processes. Studies of GSTs have revealed that genetic polymorphisms are present in these enzymes and that some of these are Loss-of-Function (LoF) variants, which affect enzymatic functions and are related to different aspects of human health. The aim of this study was to analyze functional genetic differences in GST enzymes among human populations. Attention was focused on LoF polymorphisms of GSTA1, GSTM1, GSTO1, GSTO2, GSTP1 and GSTT1 genes. These LoF variants were analyzed in 668 individuals belonging to six human groups with different ethnic backgrounds: Amhara and Oromo from Ethiopia; Colorado and Cayapa Amerindians and African Ecuadorians from Ecuador; and one sample from central Italy. The HapMap database was used to compare our data with reference populations and to analyze the haplotype and Linkage Disequilibrium diversity in different ethnic groups. Our results highlighted that ethnicity strongly affects the genetic variability of GST enzymes. In particular, GST haplotypes/variants with functional impact showed significant differences in human populations, according to their ethnic background. These data underline that human populations have different structures in detoxification genes, suggesting that these ethnic differences influence disease risk or response to drugs and therefore have implications for genetic association studies involving GST enzymes. In conclusion, our investigation provides data about the distribution of important LoF variants in GST genes in human populations. This information may be useful for designing and interpreting genetic association studies.

Keratin 8 sequence variants in patients with pancreatitis and pancreatic cancer.

Keratin 8 (KRT8) is one of the major intermediate filament proteins expressed in single-layered epithelia of the gastrointestinal tract. Transgenic mice over-expressing human KRT8 display pancreatic mononuclear infiltration, interstitial fibrosis and dysplasia of acinar cells resulting in exocrine pancreatic insufficiency. These experimental data are in accordance with a recent report describing an association between KRT8 variations and chronic pancreatitis. This prompted us to investigate KRT8 polymorphisms in patients with pancreatic disorders. The KRT8 Y54H and G62C polymorphisms were assessed in a cohort of patients with acute and chronic pancreatitis of various aetiologies or pancreatic cancer originating from Austria (n=16), the Czech Republic (n=90), Germany (n=1698), Great Britain (n=36), India (n=60), Italy (n=143), the Netherlands (n=128), Romania (n=3), Spain (n=133), and Switzerland (n=129). We also studied 4,234 control subjects from these countries and 1,492 control subjects originating from Benin, Cameroon, Ethiopia, Ecuador, and Turkey. Polymorphisms were analysed by melting curve analysis with fluorescence resonance energy transfer probes. The frequency of G62C did not differ between patients with acute or chronic pancreatitis, pancreatic adenocarcinoma and control individuals. The frequency of G62C varied in European populations from 0.4 to 3.8%, showing a northwest to southeast decline. The Y54H alteration was not detected in any of the 2,436 patients. Only 3/4,580 (0.07%) European, Turkish and Indian control subjects were heterozygous for Y54H in contrast to 34/951 (3.6%) control subjects of African descent. Our data suggest that the KRT8 alterations, Y54H and G62C, do not predispose patients to the development of pancreatitis or pancreatic cancer.

PI, GC, HP, and TF serum protein polymorphisms in Siena, Tuscany, Italy, with a review of data for Italy

The genetic polymorphism of four serum proteins (PI, GC, HP, and TF) is analyzed in a sample of 200 unrelated individuals from the province of Siena, Tuscany, central Italy. Siena is traditionally divided into 17 Contrade, that act as social units. The aim of this report is to ascertain whether this peculiar organization has led to genetic differentiation among the inhabitants of each Contrada and from other populations of Italy. For this purpose, the frequencies of genetic markers found in Siena are also compared with those reported for the same serum proteins in Italy based on provincial samples from the literature. The statistical analyses (heterozygosity estimates, F‐statistics, and cluster analysis) suggest that the Contrade represent only a cultural and historical institution without biological consequence and that the Italian population can be considered genetically homogeneous. Am. J. Hum. Biol. 9:629–646, 1997.

Human GST loci as markers of evolutionary forces: GSTO1*E155del and GSTO1*E208K polymorphisms may be under natural selection induced by environmental arsenic

Over the last two decades, significant data has been accumulated linking Glutatione S-Transferases (GSTs) with the development of several diseases. Contemporary studies have demonstrated the impact of ethnicity on GST allele frequencies. The aim is to verify if the variability of GST genes reflects population demographic history or rather selective pressures. GST genes (GSTM1, GSTO1 GSTO2, GSTT1) were analysed in three Ecuadorian populations (Cayapas, n = 114; Colorados, n = 104; African-Ecuadorian, n = 77) and compared with HapMap data. GST SNPs were determined using the PCR-RFLP method while GST null phenotype was determined using a Multiplex PCR. The population relationship achieved using GSTM1 positive/null, GSTO1*A140D, GSTO2*N142D and GSTT1 positive/null are in agreement with the data obtained using neutral polymorphisms: Amerindians are close to Asian populations and African-Ecuadorians to African populations. To what concerns GSTO1*del155 and GSTO1*K208 variants, allele frequencies never exceeded 10%, showing no significant differences in the Ecuadorian groups and in worldwide populations. The features of GSTO1*del155 and GSTO1*K208 variants and their association with arsenic biotransformation deficiency suggest the presence of a selection mechanism towards these loci. In particular, this hypothesis is strengthened by a possible linkage between these alleles and the susceptibility of arsenic-induced male infertility.

An anthropogenetic study on the Oromo and Amhara of central Ethiopia

Blood samples from members of the Oromo and Amhara ethnic groups of central Ethiopia were tested for 10 erythrocyte protein systems: ACP1, ADA, AK1, CA2, ESD, G6PD, GLO1, HBβ, PGD, and PGM1. Differences between the two samples were relatively slight and not statistically significant. Gene frequency distributions were then analyzed in the context of the genetics of the African and Arabian peoples. Considering the erythrocyte enzyme data, the Oromo and Amhara appear quite similar to Europoids (particularly to the South Arabians) and considerably different from the Negritic peoples. There is evidence for close genetic affinity among the Cushitic‐ and Semitic‐speaking population groups of the Horn. Admixture between Europoid and Negritic populations seems to have been the main microevolutionary factor in generating the present day Cushitic (and Semitic)‐speaking group of eastern Africa. The results are consistent with the hypothesis, supported by historical and linguistic evidence, for a common origin of these groups from a Cushitic‐speaking group living in eastern Africa.

Linking between genetic structure and geographical distance: Study of the maternal gene pool in the Ethiopian population

Abstract Background The correlation between genetics and geographical distance has already been examined through the study of the dispersion of human populations, especially in terms of uniparental genetic markers. Aim The present work characterises, at the level of the mitochondrial DNA (mtDNA), two new samples of Amhara and Oromo populations from Ethiopia to evaluate the possible pattern of distribution for mtDNA variation and to test the hypothesis of the Isolation-by-Distance (IBD) model among African, European and Middle-Eastern populations. Subjects and methods This study analysed 173 individuals belonging to two ethnic groups of Ethiopia, Amhara and Oromo, by assaying HVS-I and HVS-II of mtDNA D-loop and informative coding region SNPs of mtDNA. Results The analysis suggests a relationship between genetic and geographic distances, affirming that the mtDNA pool of Africa, Europe and the Middle East might be coherent with the IBD model. Moreover, the mtDNA gene pools of the Sub-Saharan African and Mediterranean populations were very different. Conclusion In this study the pattern of mtDNA distribution, beginning with the Ethiopian plateau, was tested in the IBD model. It could be affirmed that, on a continent scale, the mtDNA pool of Africa, Europe and the Middle East might fall under the IBD model.

Marriage distances among the Afroamericans of Bluefields, Nicaragua

In a sample of 311 couples from the Afroamerican community of Bluefields, Eastern Nicaragua, the distribution of matrimonial distance shows a deviation from the leptokurtic rule. This results from assortative mating among the population.