IF YOU WERE born in the United States within the last 50 or so years, chances are good that one of the first things you did as a baby was give a DNA sample to the government. By the 1970s, states had established newborn screening programs, in which a nurse takes a few drops of blood from a pinprick on a baby’s heel, then sends the sample to a lab to test for certain diseases. Over the years, the list has grown from just a few conditions to dozens.