The saving switch.

The epigenome consists of a system of chemical tags that attach to our DNA and its associated molecules, switching genes on and off. But the system is not without glitches-and scientists think that the misplacement of these tags can cause disease. This idea has led to new drugs that aim to correct gene activity (and obliterate disease) by altering the proteins around which DNA winds. Cassandra Willyard examines whether this approach will unlock the long-awaited promise of epigenetic therapy.