Detailed genetic study reveals lasting contributions from British, Norse and Norman invasions

A genome-wide study of the people of Ireland reveals a previously hidden genetic landscape shaped by geography and historical migrations. Ross Byrne and Russell McLaughlin of Trinity College Dublin in Ireland report their findings on January 25, 2018 in PLOS genetics.

Over the 10,000 years that people have continuously inhabited the Emerald Isle, they have established distinct cultural and geographic regions. Previous studies, however, had found no clear genetic clusters within the Irish population. In the current study, the researchers looked in more detail at the genetic diversity across the islands. They analyzed genetic variation on nearly 1,000 Irish genomes and more than 6,000 genomes from Britain and mainland Europe. The study revealed 23 distinct Irish genetic clusters, separated by geography. The clusters are more distinct in the west of Ireland, but less pronounced in the east, where historical migrations have erased genetic divisions. When the researchers took into account the genetic contributions of people of British ancestry, a clear pattern emerged, showing that contributions from Britain were declining in western populations. Researchers also detected genetic inputs from Europe and estimated the timing of historical Norse-Viking and Anglo-Norman migrations to Ireland, which yielded dates consistent with historical records.

The study paints a new and more complex picture of the genetic landscape of Ireland and demonstrates the signatures that historical migrations have left on the modern Irish genome. The results also show that a distinct genetic structure can exist even within small isolated populations. The researchers suggest that this newly revealed structure should be considered in future studies that use the Irish population to identify the genetics underlying various traits and diseases.

Commenting on the impact of the study, Ross P. Byrne said, “This subtle genetic structure in such a small country has implications for medical genetic association studies. variation, which can potentially lead to the emergence of false positive results. We believe this will be particularly important in the analysis of rare variants as these are expected to be less evenly distributed within a country. We intend to explore this further and determine if this structure should be considered in fixes. Russell McLaughlin adds: “Ireland’s long and complex history of population dynamics has left an indelible mark on the genomes of the island’s modern inhabitants. We have shown that using only genetic data, we can accurately reconstruct elements of this past and demonstrate a striking correlation between geographic provenance and genetic affinity. Understanding this fine-grained population structure is critically important for ongoing and future studies of rare genetic variation in health and disease.”

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