Babies born with spinal muscular atrophy often live brief, heartbreaking lives. They miss key developmental milestones. They cry weakly. They can’t roll over. They never sit up on their own or feed themselves.
The disease occurs when the body is starved of a protein so vital for movement that it’s literally called the “survival of motor neuron” protein, or SMN. You inherit two copies of the primary gene that codes for that protein, one from each of your parents. If one is flawed, the good one will cover for it, and you may never know you carry a mutation. But about one in every 10,000 kids gets two bad copies.
For decades, scientists have dreamed of curing diseases such as spinal muscular atrophy—diseases born of a single genetic glitch—by replacing the flawed gene with a working one. Progress toward this goal has proven excruciatingly slow.