For the first time, scientists 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 Project, 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: For example, if someone's genome contains DNA associated with cancer, but that DNA is "crossed out" by molecules in the epigenome, 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.
Sequencing genomes is the centerpiece of President Barack Obama's "precision medicine" initiative. "The only way you can deliver on the promise of precision medicine is by including the epigenome," said MIT's Manolis Kellis, who led the mapping project.
Because scientists involved in the project have been depositing their findings in a public database as they went along, other researchers have been analyzing the information even before the map was formally published. One of the resulting studies shows, for instance, that brain cells from people who died with Alzheimer's disease had epigenetic changes in DNA involved in immune response.