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Finnish Population Genetic Analysis Reflects Recent Historical Events

NEW YORK – A University of Helsinki-led team has retraced population genetic patterns in Finland over more than six decades, including ancestry changes following significant events in the country and world at large — from urbanization in the 1950s to the population effects of World War II.

"To our knowledge, this is the first study to track geographically the annual genetic contributions of sub-populations within a single European country," senior author Matti Pirinen, a researcher affiliated with the University of Helsinki Institute of Molecular Medicine Finland and the university's public health department, and his colleagues wrote, adding that the study "concretely demonstrates continuous genetic mixing within current human populations."

Using array-based genotyping profiles, together with available computational tools, the researchers teased out individual-level ancestry tracts for almost 18,500 participants in Finland's national Finrisk study, representing a dozen parts of the country. Their findings, published in PLOS Genetics on Thursday, revealed fine-mapped population shifts involving 10 ancestral groups that were more or less prominent in different parts of the country over time.

"It is nice to see how modern computational tools can detect such population movements even at an accuracy of one year using genetic ancestry estimation within a single European country," Pirinen said in an email, noting that a similar approach can be applied to other populations, including those in nearby sites in Sweden, Russia, and Estonia.

The fine-scale ancestry patterns identified in Finland and in other parts of the world may prove useful for interpreting genetic tests and predicting disease risk, Pirinen explained, noting that risk prediction tools "may perform differently depending on the genetic background of an individual."

"We expect that our results help personalizing future genomic medicine in the Finnish population," he and his co-authors wrote, "and promote the participation of [the] general public in large-scale biobank collections that provide unprecedented opportunities for human genetic research, in Finland as well as elsewhere in the world."

With the help of several haplotype-based computational tools, the team considered ancestry in 18,463 individuals from the Finrisk study in the context of their location and birth year in relation to 10 Finnish reference ancestry groups and 15 geography-based populations in Finland. Based on these data, they retraced detailed population structure changes in light of broader historical events in 12 Finnish regions from 1923 to 1987.

In the 1900s, for example, the investigators saw signs of population movement from eastern Finland to western parts of the country, with eastern Finnish ancestry tracts becoming more prevalent in the west.

Between the late 1930s and around 1945, on the other hand, they identified an influx of ancestry from southeast Finland into other parts of the country, as members of the Karelian population evacuated a region lost to the Soviet Union during World War II. 

"We detected major changes after a sudden, internal migration related to World War II from the region of ceded Karelia to the other parts of the country as well as the effect of urbanization starting from the 1950s," the authors reported, noting that "while the level of genetic heterogeneity in general increases toward the present day, its rate of change has considerable differences between the regions."