Genetic link to diseases in mixed populations decoded

Washington, (IANS) Understanding the genetic ancestry of mixed populations can not only help to detect their origins but also to understand the genetic basis of complex diseases, says a new study.

It is the first time that the genomes of individuals of admixed ancestry have been sequenced in such detail, says Francisco De La Vega of Life Technologies, Foster City, California, the US.

Working with Carlos Bustamante, professor and his team in the Department of Genetics at Stanford University, the scientists analysed the genomes of two people - one of African-American and one of Hispanic-Latino origin.

The majority of the personal genomes sequenced to date come from individuals of either European, African or Asian descent, because it is in these groups that most genetic disease association studies are being carried out.

However, populations where genetic mixing through migration has taken place relatively recently make up a sizable proportion of the world's population, and have not been well studied to date because of the complexity of dealing
with the contributions of genes from different ancestries in disease.

"We set out to provide a better understanding of the genome structure in admixed populations by sequencing one African-American and one Mexican sample," said De La Vega.

"By analysing genetic variants in mixed people whose frequency differs in the ancestral populations, we can work out the ancestry of different chromosomal segments in an individual," added De La Vega.

"This has already been done in a number of different ways. The difference with our work is that, by using whole genome sequencing using the Solid System, we can greatly increase the resolution of our analyses and achieve a very much clearer picture of the ancestry of genome sequences for the individuals studied," said De La Vega.

"We already know that present-day African-Americans trace their ancestry to a rich mosaic of migrants from the mainly west African and northern European populations who settled in North America and the Caribbean.

Mexicans, on the other hand, are descendants of Meso-American indigenous populations - themselves derived from population migrations from Asia (through the Bering straits) - and largely Southern European (mainly Spanish) settlers", said De La Vega.

"But the added value of our research is that we can show the approximate number of generations at which the genetic mixing occurred, estimate the rate at which admixture occurred, and understand better the genetic diversity in the ancestral populations."

To date there are few comprehensive studies of genetic diversity in native populations in the Americas, and by analysing them scientists can begin to piece together the population history of both the admixed and indigenous populations.

They can also begin to analyse the contribution of native American genetic variants to the disease burden in the Americas of today, something which at present is relatively unknown.

"We believe that our work will help move forward genetic disease association studies in these admixed populations," said De La Vega.

The scientists intend to follow up their work by sequencing many more genomes of different populations in the Americas in order to understand further differentiation within the continent and the frequency of the genetic variants, said a release of Life Technologies.

These findings were presented at the annual conference of the European Society of Human Genetics.