FedEx, UPS, DHL—when it comes to sending packages, choices abound. But the most important delivery service you may not have heard of? mRNA. That’s short for messenger RNA, which is how your DNA sends blueprints to the protein-assembly factories of your cells. When a protein is faulty, delivering synthetic mRNA to cells could trigger production of a functional version. And that’s a message people with a variety of genetic diseases want to hear.