A massive search for a prime suspect in the mystery of the missing heritability has come up empty.
Known as copy-number variations, or CNVs, these extra or missing sequences of the genome have been linked to some rare diseases. Researchers thought they might play a role in common diseases, too. But a comparison of 19,000 genomes found few links to breast cancer, diabetes and six other major killers.
Copy-number variations "are unlikely to contribute to the genetic basis of common human diseases," wrote researchers from the Wellcome Trust Case Control Consortium in a study published March 31 in Nature.
Formed during glitches in gene duplication, CNVs cover as much space on the genome as standard gene mutations, in which individual letters of the genetic code are mixed up.
Standard gene mutations don't appear to explain much of the heredity that clearly exists in many common diseases, a phenomenon that scientists call "missing heritability." To find whether CNVs might play a part, Wellcome Trust researchers compared CNVs in the genomes of 3,000 healthy people with CNVs in the genomes of 16,000 patients. The patients were equally divided among people with type 1 and type 2 diabetes, bipolar disorder, rheumatoid arthritis, breast cancer, high blood pressure, heart disease and Crohn's disease.
But when the numbers were crunched, CNVs were cleared. No individual CNVs had a powerful effect on disease, nor did large numbers of them.
Though some rare CNVs are linked to disease, and more remain to be found, the bulk appear to do nothing, wrote the researchers.
The missing heritability is still at large.
Image: Mike Towber/Flickr
See Also:
- Whew! Your DNA Isn't Your Destiny
- Beyond the Genome
- Exploring the Genetic Differences Between Chimps and Humans
- The Human Genome in 3 Dimensions
Citation: "Genome-wide association study of CNVs in 16,000 cases of eight common diseases and 3,000 shared controls." By the Wellcome Trust Case Control Consortium. Nature, Vol. 464 No. 7289, April 1, 2010.
Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
