A genome-wide study of the people of Ireland has uncovered a more diverse genetic landscape than previous studies have suggested. Published last week in the journal PLOS Genetics, the study shows that the modern Irish genome has been shaped by geography and historical migrations. The findings also show that even small, isolated populations can have distinct genetic structures.
Ireland has been continuously inhabited for around 10,000 years. Despite the distinct cultural and geographic regions that have developed during that time, previous studies found no clear genetic groups within the Irish population. Led by Ross Byrne of Trinity College Dublin in Ireland, a team of researchers more closely examined genetic diversity across Europe and revealed a more complex picture in Ireland.
The team used over 6,000 genomes from Britain and mainland Europe, and nearly 1,000 genomes from Ireland. Their research uncovered 23 different Irish genetic clusters that were separated by geography. Western Ireland showed more diversity of genetic clusters, while eastern Ireland showed more homogeneity. Genetic contributions from people with British ancestry also differed between eastern and western Ireland; the most genetic input was detected in the east and slowly dropped off in populations further west.
These differences are due to historical migrations in the east that eroded the region’s older genetic structure, according to the researchers. Because settlement was concentrated in the east, longstanding Celtic diversity remained in the west.
The study also found genetic input from elsewhere in Europe. Using genetic data alone, the team was able to date key migration events into Ireland from Europe and Britain. Their results were consistent with historical records of Viking and Norman invasions, which they say demonstrates the impact these migrations have had on the on modern Irish genome.
Their findings have “important implications for population-based genetic association studies,” the authors say. They encourage others to take into account this new structure when designing future medical genetic association studies. Studies that examine rare genetic variation and its association with traits could especially benefit, since these types variants are often less uniformly distributed.
Byrne noted, “current corrections for population structure in study designs may not adequately account for this within country variation, which may potentially lead to false positive results emerging.” He said he and the team “intend to explore this further and identify if this structure should be accounted for in corrections.”
Russell McLaughlin of Trinity College’s Molecular Population Genetics Lab added, “The long and complex history of population dynamics in Ireland has left an indelible mark on the genomes of modern inhabitants of the island. We have shown that, using only genetic data, we can accurately reconstruct elements of this past and demonstrate a striking correlation between geographical provenance and genetic affinity.”
McLaughlin also emphasized the importance of the findings for future research: “Understanding this fine-grained population structure is crucially important for ongoing and future studies of rare genetic variation in health and disease.”