European admixture on the Micronesian island of Kosrae: lessons from complete genetic information

The architecture of natural variation present in a contemporary population is a result of multiple population genetic forces, including population bottleneck and expansion, selection, drift, and admixture. We seek to untangle the contribution of admixture to genetic diversity on the Micronesian island of Kosrae. Toward this goal, we used a complete genetic approach by combining a dense genome-wide map of 100 000 single-nucleotide polymorphisms (SNPs) with data from uniparental markers from the mitochondrial genome and the nonrecombining portion of the Y chromosome. These markers were typed in ∼3200 individuals from Kosrae, representing 80% of the adult population of the island. We developed novel software that uses SNP data to delineate ancestry for individual segments of the genome. Through this analysis, we determined that 39% of Kosraens have some European ancestry. However, the vast majority of admixed individuals (77%) have European alleles spanning less than 10% of their genomes. Data from uniparental markers show most of this admixture to be male, introduced in the late nineteenth century. Furthermore, pedigree analysis shows that the majority of European admixture on Kosrae is because of the contribution of one individual. This approach shows the benefit of combining information from autosomal and uniparental polymorphisms and provides new methodology for determining ancestry in a population

High Differentiation among Eight Villages in a Secluded Area of Sardinia Revealed by Genome-Wide High Density SNPs Analysis

To better design association studies for complex traits in isolated populations it's important to understand how history and isolation moulded the genetic features of different communities. Population isolates should not “a priori” be considered homogeneous, even if the communities are not distant and part of a small region. We studied a particular area of Sardinia called Ogliastra, characterized by the presence of several distinct villages that display different history, immigration events and population size. Cultural and geographic isolation characterized the history of these communities. We determined LD parameters in 8 villages and defined population structure through high density SNPs (about 360 K) on 360 unrelated people (45 selected samples from each village). These isolates showed differences in LD values and LD map length. Five of these villages show high LD values probably due to their reduced population size and extreme isolation. High genetic differentiation among villages was detected. Moreover population structure analysis revealed a high correlation between genetic and geographic distances. Our study indicates that history, geography and biodemography have influenced the genetic features of Ogliastra communities producing differences in LD and population structure. All these data demonstrate that we can consider each village an isolate with specific characteristics. We suggest that, in order to optimize the study design of complex traits, a thorough characterization of genetic features is useful to identify the presence of sub-populations and stratification within genetic isolates

Mitochondrial DNA sequence analysis in Sicily

This study reports data on the sequences of the first hypervariable segment of a sample of the Sicilian population from Alia (Palermo, Italy). The results show the presence of 32 different haplotypes in the 49 individuals examined. The average number of pairwise nucleotide differences was 4.04, i.e., 1.17% per nucleotide. The distribution of the nucleotide differences matches the theoretical distribution and indicates only one major episode of expansion that occurred between 20,732 and 59,691 years ago, between the Middle Paleolithic and Upper Paleolithic. Compared with the other populations, parameters of the Sicilian sample lie in an intermediate position between the eastern and western Mediterranean populations. This is due to numerous contacts that Sicily has had with the Mediterranean area since prehistoric times. At the same time, the singularity of some of the haplotypes present in the sample studied indicates the persistence of some characteristics caused by genetic drift and isolation that the population has endured in the course of its history. (C) 2001 Wiley-Liss, Inc

24 bp duplication of CHIT1 gene is not correlated with coronary artery disease in Corsica Island (France)

In this study we analyzed allele and genotype distributions of 24 bp duplication of the CHIT1 gene in a sample of patients (N=300) with coronary artery disease (CAD) and in a control group (N= 300) from central Corsica (France), with the aim to investigate the possible association between CHIT1 genotypes and CAD in Corsican population. Serum chitotriosidase activity is increased in individuals experiencing an ischemic stroke of atherothrombotic etiology and in subjects with ischemic heart disease. Our results suggest that 24 bp duplication of CHIT1 gene is not correlated with CAD in Corsican population, according to a previous study carried out on a Spanish sample. Gene prevalence and perhaps gene-disease associations vary according to ethnicity. Further studies, based on different ethnic groups, could be suitable to determine the implication of this polymorphism with respect to CAD

Prevalence and trend of overweight and obesity among Sardinian conscripts (Italy) of 1969 and 1998

This study evaluated the prevalence of overweight and obesity in the male Sardinian population (Italy), and verifies that it has increased over the last 30 years. Data were collected during 2003-2004 from military registers in the Archive of the Military District of Cagliari for the years 1969 and 1998. A total of 22,345 forms were analysed from all Sardinia. The conscripts were classified on the basis of their place of residence and socioeconomic status. The overall prevalence of overweight and obesity in Sardinia were 4.33% and 0.55%, respectively, for the conscripts of 1969 and 9.8% and 3% for 1998. Olbia-Tempio (northern Sardinia) was the province with the highest incidence of overweight and obesity in 1969, and Nuoro (central Sardinia) had the highest incidence in 1998. Distribution of body mass index, overweight and obesity across the island showed a statistically significant heterogeneity that strongly decreased from 1969 to 1998. Among the conscripts of 1969, the incidence of overweight and obesity were higher in rural than in urban regions. An opposite trend was observed for the 1998 prevalence, it being more frequent in urban than rural regions. Comparison with other Italian regions was made. The percentages of overweight and obese individuals in Sardinia have markedly increased during the last 30 years, but their low incidence with respect to other Italian populations could be explained by the genetic peculiarity of the island. The change in the internal distribution of obesity clearly reflects socioeconomic changes

Italian isolates today: geographic and linguistic factors shaping human biodiversity

We briefly review the current status of anthropological and genetic studies of isolated populations and of their micro-evolutionary and biomedical applications, with particular emphasis on European populations. Thereafter, we describe the ongoing collaborative research project "Isolating the Isolates: geographic and cultural factors of human genetic variation" regarding Italian extant geographical and/or linguistic isolates, aimed at overcoming the limitations of previous studies regarding geographical coverage of isolates, number and type of genetic polymorphisms under study and suitability of the experimental design to investigate gene-culture coevolutionary processes. An interdisciplinary sampling approach will make it possible to collect several linguistic isolates and their geographic neighbours from Trentino, Veneto, Friuli, Tuscany, Sardinia and Calabria. This will be coupled with a shared genotyping strategy based on mitochondrial and Y-chromosomal polymorphisms. The results will be analyzed with a focus on the role of geographical and cultural factors in shaping human biodiversity. The aims of the project go beyond the simple reconstruction of the genetic structure and history of the examined groups. In fact, the study will also include an assessment for future bio-medical studies and the development of genetic and bio-demographic databases. Ethical and educational aspects are also foreseen by the project, by using informed consents together with disseminating activities in loco, completed by the creation of a dedicated web site for both scientific and public audiences