The Broad group and others are now using microarrays that look for copy number variations to study a variety of common diseases. "In the next couple of years, we should really start to see new insights into the disease-causing mechanisms that result from this kind of mechanism," says Hurles. In fact, two such studies have already yielded important insights, identifying rare deletions linked to autism and schizophrenia. "If we can interrogate both kinds of variation in the same patient in the same experiment, we can get an integrated understanding of how variations come together to influence disease," says Steven McCarroll, a geneticist at the Broad and lead author of the paper.

Still, some types of copy number variations may be going undetected. In a second paper published in Nature Genetics, Greg Cooper and his colleagues at the University of Washington compared data collected using microarrays sold by Illumina with a sequencing-based assay published last year. They found that the array missed a number of changes centered on so-called hot spots, where multiple duplications--a string of four or five copies of a gene--make DNA difficult to study. Cooper says that different approaches will likely be needed to study these changes.

"The more detail we can get about our genomes--each peeling of the layer of the onion--teaches us more about disease," says Altshuler. "The technology is moving in parallel, so as we move further, we can investigate each layer in detail."