December 21, 2012

Genetic isolates from Friuli

Just a quick mention of this paper on selected rare populations of Friuli because I totally fail to see the angle of interest in this paper, yet, together with other data may be of interest for European population genetics... potentially.

Tõnu Esko et al., Genetic characterization of northeastern Italian population isolates in the context of broader European genetic diversity. European Journal of Human Genertics, 2012. Open accessLINK [doi: 10.1038/ejhg.2012.229]

Abstract

Population genetic studies on European populations have highlighted Italy as one of genetically most diverse regions. This is possibly due to the country’s complex demographic history and large variability in terrain throughout the territory. This is the reason why Italy is enriched for population isolates, Sardinia being the best-known example. As the population isolates have a great potential in disease-causing genetic variants identification, we aimed to genetically characterize a region from northeastern Italy, which is known for isolated communities. Total of 1310 samples, collected from six geographically isolated villages, were genotyped at >145 000 single-nucleotide polymorphism positions. Newly genotyped data were analyzed jointly with the available genome-wide data sets of individuals of European descent, including several population isolates. Despite the linguistic differences and geographical isolation the village populations still show the greatest genetic similarity to other Italian samples. The genetic isolation and small effective population size of the village populations is manifested by higher levels of genomic homozygosity and elevated linkage disequilibrium. These estimates become even more striking when the detected substructure is taken into account. The observed level of genetic isolation in Friuli-Venezia Giulia region is more extreme according to several measures of isolation compared with Sardinians, French Basques and northern Finns, thus proving the status of an isolate.

Fig. 2
Model-based mapping convergence with SPA. Label position indicates the (a) specific PC1 and PC2 coordinate values for each individual and (b) the mean PC1 and PC2 coordinate values for each population. For (a, b), the colors have a following meaning: (1) dark blue color: a homogeneous fraction of the FVG population; a blue color: more general fraction of the FVG population; a red color: other Italian samples; a violet color: Basques; an orange color: Slovenians; and green color: all other populations. For (a, b), the following population abbreviation labels are used: AT, Austrians; BA, French Basques; BG, Bulgarians; BO, Borbera; CA, Carlantino; CL, Clauzetto; CH, Swiss; CZ, Czechs; GR, Germans; ER, Erto; ES, Spaniards; FR, French; HU, Hungarians; IL, Illegio; IT, Italians; JW_A, Ashkenazy Jews; JW_S, Sephardic Jews; OR, Orcadians; RE, Resia; RO, Romanians; SA, Sardinians; SA_, Sauris; SMC, San Martino del Carso; SI, Slovenians; TU, Tuscans. The extra abbreviations: N, northern; S, southern; I, a more homogeneous sub-population; G, a more general sub-population.


3 comments:

  1. Is there any indication of how this population came to be so isolated? Geographically, you'd expect people at such a crossroads to be heavily admixed, and I have no familiarity with the cultural dimensions.

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    Replies
    1. They are different populations in fact. All but one in San Martino del Carso are from the Alpine mountain zone, what should explain their peculiarties (Mountain districts are always isolate). And it's all these which actually show their peculiarities (the San Martino Italian-speaker population is "normal" in fact: gradating from the North Italian to the Slovenian composite).

      The others show strong peculiarities at:

      1. Resia (K=4 but very large sample). From the paper: "people in the village of Resia speak an archaic proto-Slavic language, known as Resian, but their surnames are Italian or Italianized".

      2. Sauris (K=6). The inhabitants of village Sauris speak an archaic dialect of German origin and according to legends the locals have their ancestral roots near Tyrol.

      3. Illegio (K=7). "In the village of Illegio, not far from Resia, people speak another local language – called friuliano – of the Rhaeto-Romance language sub-family, which, during the Middle Ages, was widespread – from modern Switzerland to Slovenia. Illego is further characterized by a limited number of surnames, what could be interpreted as evidence for marginal immigration. Another layer of specific cultural heritage is added by characteristic local symbols found engraved on local houses".

      4. Erto (K=8). "Until 50 years ago, before a flood devastated the valley of origin, the main spoken language in the village of Erto was a Latin dialect called ertano, while current population is an admixture of the former inhabitants of Erto and migrants from the nearby regions".

      5. Clauzetto (K=10) "Finally, the village of Clauzetto is located in a remote valley where people speak friulano".

      The southernmost villages, Erto and Clauzetto, are located just East and West of the uninhabited National Park of the Friulian Dolomites. The other three are fully Alpine. If you look in Google Maps, you see that none of them is centric at all, much less the "crossroads" you imagine. The "crossroads" would be further South in the plains of Pordenone and Udine.

      Something I'm noticing as I write this, is that the various populations, before they "snap" as distinct do not appear too different from Sardinians (tendency to the left in the PC graph, high "pink" or Mediterranean component in the Admixture one). This may well explain the apparent autosomal affinity of Ötzi, who was a close relative of these peoples surely, with Sardinians in some studies. However these Alpine isolates also show minor continental influences ("brown" and "orange"), which could be explained as Metal Ages' input (Indoeuropeans and such).

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    2. Clearly it pays to use physical rather than political maps for this kind of thing. The descriptions above are really fascinating and point to fruitful places to look for a whole host of interesting and not widely known relatively deep stories in cultural history. I'll have to see if I can find any local histories of these places which seem like a rich first place to look for more detail.

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