If a person’s DNA is the roadmap of their lifetime health, their RNA is more of a real-time barometer, recording what happens in their body on a minute-by-minute basis. Our DNA stores and transfers genetic information, but remains little changed throughout our lives. At best, it can tell us about the probability we will someday develop various diseases — whether or not we will get cancer, for instance, or be susceptible to diabetes or heart disease — but it  can’t tell us much about our current health.