Red cell and serum protein polymorphisms in Sardinia

From old markers to next generation: reconstructing the history of the peopling of Sardinia

CONTEXT

For many years the Sardinian population has been the object of numerous studies because of its unique genetic structure. Despite the extreme abundance of papers, various aspects of the peopling and genetic structure of Sardinia still remain uncertain and sometimes controversial.

OBJECTIVE

We reviewed what has emerged from different studies, focussing on some still open questions, such as the origin of Sardinians, their relationship with the Corsican population, and the intra-regional genetic heterogeneity.

METHODS

The various issues have been addressed through the analysis of classical markers, molecular markers and, finally, genomic data through next generation sequencing.

RESULTS AND CONCLUSIONS

Although the most ancient human remains date back to the end of the Palaeolithic, Mesolithic populations brought founding lineages that left evident traces in the modern population. Then, with the Neolithic, the island underwent an important demographic expansion. Subsequently, isolation and genetic drift contributed to maintain a significant genetic heterogeneity, but preserving the overall homogeneity on a regional scale. At the same time, isolation and genetic drift contributed to differentiate Sardinia from Corsica, which saw an important gene flow from the mainland. However, the isolation did not prevent gene flow from the neighbouring populations whose contribution are still recognisable in the genome of Sardinians.

Sardinians genetic background explained by runs of homozygosity and genomic regions under positive selection

The peculiar position of Sardinia in the Mediterranean sea has rendered its population an interesting biogeographical isolate. The aim of this study was to investigate the genetic population structure, as well as to estimate Runs of Homozygosity and regions under positive selection, using about 1.2 million single nucleotide polymorphisms genotyped in 1077 Sardinian individuals. Using four different methods--fixation index, inflation factor, principal component analysis and ancestry estimation--we were able to highlight, as expected for a genetic isolate, the high internal homogeneity of the island. Sardinians showed a higher percentage of genome covered by RoHs>0.5 Mb (F(RoH%0.5)) when compared to peninsular Italians, with the only exception of the area surrounding Alghero. We furthermore identified 9 genomic regions showing signs of positive selection and, we re-captured many previously inferred signals. Other regions harbor novel candidate genes for positive selection, like TMEM252, or regions containing long non coding RNA. With the present study we confirmed the high genetic homogeneity of Sardinia that may be explained by the shared ancestry combined with the action of evolutionary forces.

Craniofacial morphometric variation and the biological history of the peopling of Sardinia

The aim of this work is to explore the pattern of craniofacial morphometric variation and the relationships among five prehistoric Sardinian groups dated from Late Neolithic to the Nuragic Period (Middle and Late Bronze Age), in order to formulate hypotheses on the peopling history of Sardinia. Biological relationships with coeval populations of central peninsular Italy were also analysed to detect influences from and towards extra-Sardinian sources. Furthermore, comparison with samples of contemporary populations from Sardinia and from continental Italy provided an indication of the trend leading to the final part of the peopling history. Finally, Upper Palaeolithic and Mesolithic samples were included in the analyses to compare the prehistoric Sardinians with some of their potential continental ancestors. The analysis is based on multivariate techniques including Mahalanobis D(2) distance, non-parametric multidimensional scaling (MDS) and principal component analysis (PCA). The results showed the tendency to progressive differentiation between Sardinian groups and peninsular Italian groups, with the possible exception of a discontinuity showed by the Bonnànaro (Early Bronze Age) Sardinian sample. Several aspects of the morphological results were found to agree with the current genetic evidence available for the present-day Sardinian population and a Nuragic sample: (1) biological divergence between the Sardinian and peninsular Italian populations; (2) similarity/continuity among Neolithic, Bronze Age and recent Sardinians; (3) biological separation between the Nuragic and Etruscan populations; (4) contribution of a Palaeo-Mesolithic gene pool to the genetic structure of current Sardinians.

Genetics, geography, and culture: the population of S. Pietro Island (Sardinia, Italy)

An interesting aspect of the island of Sardinia (Italy) is the wide range of genetic variability within the island itself. The variability is widened by the presence of some populations of different ethnic origin who speak a language other than Sardinian. This work deals with the study of the genetic structure of the Carloforte population which inhabits the tiny island of S. Pietro 4 km off the southwest coast of Sardinia. S. Pietro was first populated in 1738 by emigrants coming from the island of Tabarka (Tunisia) who spoke an archaic form of the Ligurian dialect. Data on genetic polymorphisms in the Carloforte population are presented and discussed in relation to some Sardinian and Italian populations. Data on demographic and matrimonial structure are also presented. The genetic analyses show the Carloforte population as being clearly separated from both Sardinians and continental Italians. The isolation of Carloforte, highlighted by language diversity, endogamy, and consanguinity levels and marriage area, supports the idea of genetic diversity linked to cultural peculiarity.