A massive genetic study carried out in the United Kingdom has pinpointed 24 genetic markers that increase risk for illnesses such as diabetes, arthritis, and Crohn’s disease, a form of inflammatory bowel disease. The findings illustrate the success of a new approach to gene hunting known as genome-wide association, made possible by recent advances in gene-sequencing technologies. The results were published in this week’s issue of Nature.
“This is a powerful way of identifying genes for common diseases,” says Anne Bowcock, a geneticist at Washington University Medical School, in Saint Louis. “These genes will point to altered pathways that will then point to novel therapies.”
Scientists analyzed 500,000 genetic markers in each of 17,000 people, making it the largest such study to date. By comparing the DNA of 2,000 patients with one of seven different diseases–Crohn’s disease, type 1 and 2 diabetes, cardiovascular disease, hypertension, rheumatoid arthritis, and bipolar disorder–with 3,000 healthy controls, researchers identified 24 genetic regions strongly linked to specific diseases: one in bipolar disorder, one in coronary-artery disease, nine in Crohn’s disease, three in rheumatoid arthritis, seven in type 1 diabetes, and three in type 2 diabetes. Known as the Wellcome Trust Case Control Consortium, the project is a collaboration among 50 different research groups.
Unlike diseases such as Huntington’s, in which a single genetic marker guarantees that the carrier will develop the disease, common diseases are triggered by a complex array of factors, including multiple genes each exerting a modest effect. Unlocking their genetic secrets has been a challenge, but recent advances in gene-sequencing technology have allowed scientists to take a new approach to gene hunting. Rather than searching through the DNA of specific target genes or afflicted families–approaches that have had little success for common diseases–scientists are scouring the entire genomes of large numbers of people.
By examining the entire genome, scientists find genes they never expected would be involved in a particular disease. And the massive size of such studies–the Wellcome study, for example, included almost 10 billion pieces of DNA–gives the statistical power needed for researchers to find genetic variations that raise the risk of disease by a modest amount.
In this case, scientists used a gene chip developed by Affymetrix, a genetic technology company based in Santa Clara, CA. The gene chip assesses 500,000 genetic markers in a single experiment. By comparing genetic variations in healthy people with those of people with the disease of interest, scientists can pinpoint genes that boost a person’s risk of the disease by as little as 20 percent.