Scientists unveil map of epigenome, a second genetic code

Scientists for the first time have mapped out the molecular "switches" that can turn on or silence individual genes in the DNA in more than 100 types of human cells, an accomplishment that reveals the complexity of genetic information and the challenges of interpreting it. 

Researchers unveiled the map of the "epigenome" in the journal Nature on Wednesday, alongside nearly two dozen related papers. The mapping effort is being carried out under a 10-year, $240 million U.S. government research program, the Roadmap Epigenomics Program, which was launched in 2008.

The human genome is the blueprint for building an individual person. The epigenome can be thought of as the cross-outs and underlinings of that blueprint: if someone's genome contains DNA associated with cancer but that DNA is "crossed out" by molecules in the epigenome, for instance, the DNA is unlikely to lead to cancer.

As sequencing individuals' genomes to infer the risk of disease becomes more common, it will become all the more important to figure out how the epigenome is influencing that risk as well as other aspects of health. Sequencing genomes is the centerpiece of the "precision medicine" initiative that U.S. President Barack Obama announced this month.

"The only way you can deliver on the promise of precision medicine is by including the epigenome," said Manolis Kellis of the Massachusetts Institute of Technology, who led the mapping that involved scientists in labs from Croatia to Canada and the United States.