Analysis of a Genetic Isolate: The Case of Carloforte (Italy)

We reviewed data collected during several studies concerning the genetic isolate of Carloforte (Sardinia, Italy) and analyzed new data on Y-chromosome markers. Carloforte is also a language island, where people still speak Tabarchino, an archaic form of Ligurian dialect. Demographic data indicate that, in the early years of its history, the Carloforte population was characterized by a high degree of endogamy and consanguinity rates that started to decrease around 1850, when marriages with Sardinian people began to occur more frequently. Cultural factors, mainly language, account for the high endogamy. Genetic data from classical markers, mtDNA, and Y-chromosome markers confirmed the strong isolation of the Carloforte population, which appears significantly different from the neighboring population of Sardinia. Analysis of mtDNA emphasizes the crucial aspect of sampling strategy—two different samplings of the same population (one based on founder surnames; the other one based on grandparents' criterion) gave different results. Founder surnames sampling is not affected by recent events, and therefore it better describes the ancestral population, whereas, grandparents' criterion sampling gives a picture of the present population, shaped by more recent events, such as migration and gene flow. This review further supports the notion that a comprehensive approach, including a detailed knowledge of the history of the population and the collection of different samplings, is essential in anthropology for reconstructing past and recent events that contributed to establishing the present genetic structure of the population. Likewise, it is essential in medical genetics to identify genes involved in complex diseases. An ideal scenario is offered by a genetic isolate with a recent, and well-documented, history, such as Carloforte, that can be a paradigm for this type of investigation.