For years scientists have been touting a disease-fighting technique called RNA interference. The idea behind it is pretty simple: By piggybacking on the body's own system for silencing genes, researchers think they could stop troublesome proteins from being produced, and, as a result, halt the damage those proteins cause. The trick, though, is that scientists have had a hard time figuring out how to make RNAi, as it's known, work on specific tissues.