The boy had a rare, incurable skin disease called junctional epidermolysis bullosa, caused by genetic mutations. People with the disease lack critical proteins that attach the outer layer of the skin to the inner layer, resulting in fragile skin with almost constant blisters and open sores. To fix that, the doctors took a small piece of the boy’s skin from an area that was OK. In the lab, they added a normal version of his bad gene to his skin cells. They grew sheets of the boy’s skin, in much the same way skin grafts are grown for burn victims....