Full-genome screening for newborn babies is now on the cards

OVER THE years, doctors have described more than 7,000 rare diseases, generally defined as those affecting fewer than one in 2,000 people. So, though individually unusual, such illnesses are collectively a serious problem—a long-tail of need which is hard to treat because patients are few in number and their symptoms often picked up too late. Three-quarters of rare diseases are genetic, and Global Genes, an American advocacy group, reckons 400m people around the world are affected by them. For medicine to do better, people with them need to be noticed earlier, preferably in the first days of their lives.