Genetic characterization of two North Italian villages: A story of isolation, ancient admixture, and genetic drift

Objectives: Population isolates represent a focus of interest because of their particular genetic history and the possibility of mapping peculiar deleterious variants. Here we investigated the pattern of genetic variation in two North Italian villages: Rotzo (RTZ) and Stoccareddo (STC), in the Asiago plateau. Materials and methods: We genotyped over 800 individuals for more than 600.000 markers. We investigated the isolation level by analyzing runs of homozygosity (ROH) and the level of population structure. Then we estimated the time of admixture and the relationship between ancient genomes and these two villages. Finally, we looked at the effect of genetic drift on deleterious variants. Results: We highlighted a different isolation level between RTZ and STC; despite the average number of ROH being similar between the two villages, RTZ shows a higher level of total homozygosity. We estimated, from different sources, that the time of admixture for the ancestors of these two populations was between 113 and 88 generations ago. We discovered that a deleterious variant in MCUB gene (rs78025076), which is linked to several lipid traits, is entirely absent in RTZ and at 1%frequency in STC. In contrast, the risk allele frequency is 2% in Europe and 2.4% in North-East Italy. Discussion: These results show the importance of a genetic characterization of geographically isolated populations. Their vast array of past history could highlight specific events in the past and help describe deleterious variants and traits distribution in different regions.