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Scientists unveil map of 'epigenome'

Book of life For the first time, scientists have mapped out the molecular "switches" that can turn on - or off - individual genes in the DNA in more than 100 types of human cells.

Researchers unveiled the map of the 'epigenome' in the journal Nature today, along with nearly two dozen related papers.

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 example, 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.

Precision medicine

Sequencing genomes is the centrepiece of the new area of "precision medicine".

"The only way you can deliver on the promise of precision medicine is by including the epigenome," says Manolis Kellis of the Massachusetts Institute of Technology, who led the mapping that involved scientists in labs across the world.

Epigenetic differences are one reason identical twins, with identical DNA, do not always develop the same genetic diseases, including cancer.

But incorporating the epigenome in precision medicine is daunting.

"A lifetime of environmental factors and lifestyle factors" influence the epigenome says Kellis.

These factors include smoking, exercising, diet, exposure to toxic chemicals and even parental nurturing, he says.

Not only will scientists have to decipher how the epigenome affects genes, they will also have to determine how the lives people lead affect their epigenome.

Early results

The epigenome map published today shows how 127 tissue and cell types differ from every other at the level of DNA.

The scientists involved in the project deposited their findings in a public database as they went along.

This meant that other researchers have been able to analyse the information before the map was formally published.

One of the resulting studies shows that brain cells from people who died with Alzheimer's disease had epigenetic changes in DNA involved in immune response. Alzheimer's has never been seen as an immune-system disorder, so the discovery opens up another possible avenue to understand and treat it.

Other researchers found that because the epigenetic signature of different kinds of cells is unique, they could predict with nearly 90 per cent accuracy where metastatic cancer originated, something that is unknown in two to five per cent of patients.

As a result, epigenetic information might offer a life-saving clue for oncologists trying to determine treatment, says senior author Shamil Sunyaev, a research geneticist at Brigham and Women's Hospital in Boston.

There is much more to come. Instead of the epigenome map being the end, says Kellis, "I very much see (it) as beginning a decade of epigenomics."