The genetic makeup of the Icelandic population has long fascinated scientists, positioning the nation as a unique laboratory for human health research. This distinct genetic profile is a direct consequence of its geographic isolation and turbulent history. The relative uniformity of the gene pool simplifies the complex task of identifying the genetic underpinnings of various diseases. This distinctiveness stems from historical settlement patterns, subsequent population isolation, and a commitment to preserving genealogical and medical data.
The Origin Story: Settlement and Isolation
The foundation of Iceland’s genetic makeup began with the arrival of settlers during the Viking Age (870–930 AD). The founding population originated from a mix of Norse people from Scandinavia and Gaelic people from the British and Irish Isles. Ancient DNA analysis shows the initial ancestry was approximately 57% Norse, with the remainder being Gaelic.
This initial settlement created a founder effect, limiting the genetic variation present in the resulting gene pool. This effect was intensified by geographical isolation and minimal immigration. Medieval Iceland also experienced repeated genetic bottlenecks through population crashes caused by famines, volcanic eruptions, and epidemics. These severe events reduced the population size, causing a substantial loss of genetic diversity through genetic drift. This resulted in the modern Icelandic population diverging significantly from its source populations, with Norse ancestry increasing to about 70% in contemporary Icelanders.
The Resulting Genetic Homogeneity
The historical forces of the founder effect and subsequent bottlenecks have resulted in a gene pool that is less heterogeneous compared to most other European populations. The overall impact of genetic drift has been a loss of variation and a reduced effective population size. Consequently, many individuals are more closely related to one another than in large, outbred populations.
This lower average heterozygosity, or less genetic difference between individuals, is a defining feature of the population. High relatedness makes it easier for researchers to track specific genetic traits and mutations through generations. Variants that are rare in larger, more diverse populations often rise to a higher frequency in Iceland, providing a less noisy genetic background for identifying genes responsible for complex diseases.
A Research Goldmine: The National Database
The unique genetic structure of Iceland is amplified by a world-class research infrastructure. The biotechnology company deCODE Genetics has been instrumental in leveraging this population for human health discoveries. They combined genetic data with the national genealogical database known as Íslendingabók, or the Book of Icelanders.
This comprehensive database records the family connections of nearly every Icelander who has ever lived, tracing ancestry back over 1,100 years. The information is compiled from historical sources, including church records, censuses, and inhabitant registers. This meticulous record-keeping allows for highly accurate pedigree tracing.
This combined resource is a powerful tool for gene-hunting. By linking the genetic data with the extensive health records maintained by the national healthcare system, researchers can easily connect specific genetic variants (genotype) to observable health characteristics (phenotype). DeCODE Genetics has genotyped and whole-genome sequenced tens of thousands of Icelanders who provided consent.
Specific Genetic Insights and Discoveries
The research conducted in Iceland has yielded significant breakthroughs in understanding the genetic basis of human health and disease. The focused nature of the population allows for the identification of variants that might be masked or too rare to detect in larger populations. For instance, a genetic risk factor for osteoporosis was discovered by mining the genealogical database.
Specific single nucleotide polymorphisms (SNPs) and other variants linked to common disorders have been successfully pinpointed. Researchers have identified genes that increase the risk of conditions such as stroke and myocardial infarction. The study of genetic variants has also contributed to a deeper understanding of complex psychiatric disorders, including schizophrenia.
Recent studies utilizing whole-genome sequences have demonstrated the clinical relevance of these findings, linking rare pathogenic variants to traits like reduced lifespan. A specific variant, BARD1 Cys557Ser, which confers a risk for breast cancer, rose in frequency due to a population bottleneck. These discoveries illustrate how historical events directly impact current disease prevalence and provide general insights into human biology and disease mechanisms.