Northern Europeans Differ from Southern Europeans
An international team of scientists lead by researchers at UC Davis Health System has found that genetically, modern Europeans fall into two groups: Northern and Southern (Mediterranean).
The findings, published in Public Library of Science Genetics, provide a method for scientists to take into account European ancestry when looking for genes involved in diseases.
"Until now, little has been known about the distribution of genetic variation in European populations and how much that distribution matters in terms of doing genetic studies" said Michael Seldin, chair of the Rowe Program in Genetics. "Now we will be able to control for these differences in European populations in our efforts to find genes that cause common diseases".
Seldin and his colleagues compared genetic data for 928 individuals. They studied 5,700 single nucleotide polymorphisms
(SNPs). SNPs are changes in which a single base in the DNA differs from the usual base at that position.
The human genome contains millions of them. Some SNPs cause disease, like the one responsible for sickle cell anemia. Others are normal variations in the genome. People with common ancestry will have many SNPs in common.
They tried to find these SNPs among Europeans. "We saw a clustering of individuals that come from either southern Europe or derived from populations that left southern Europe, or the Mediterranean, in the last 2,000 years", Seldin said.
The team identified a set of 400 informative SNP markers that scientists could now use to control for European ancestry when conducting genetic studies of disease, response to drug treatment, or side effects from therapy.
The data are also of interest to study historical human migrations. The Southern grouping included individuals from the Mediterranean zone (Greece, Italy, Portugal and Spain), as well as Ashkenazi and Sephardic Jews. The Northern group included people with English, Irish, German, Swedish and Ukranian ancestry. These groups correspond to those historically and geographically divided by the Pyrenees and Alps mountain ranges.
Previous studies have found four distinct genetic human populations (groups) which SNPs correlate broadly with continental ancestry: Asia, Africa, Oceania, America and continental Europe. The new study further subdivides people with European ancestry into the Northern and Southern groups.
The researchers analyzed two sets of data to prove this. They looked at SNPs associated with rheumatoid arthritis and found that, when they corrected for ancestry, several of the genes that were previously believed to be good candidates for being involved in the disease were no longer candidates at all. They also corrected for ancestry in a data set looking at lactose intolerance. "When we did not control for differences in population structure, we got a lot of false associations", Seldin explained.
Seldin and his colleagues will soon be expanding the current European study by looking at 500,000 SNPs. They also have plans for similar studies of other continental populations and for further defining different subpopulations.
Seldin said studies of other continents and ethnic groups are necessary if science is to get the most out of the advances made by the Human Genome Project. "The ultimate aim of these studies is to be able to better define subgroups and use this information to eliminate false associations, giving us a better chance of finding true associations for disease genes", Seldin said.
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