Sweeney’s plan was to introduce the dystrophin gene by hitching it to the DNA of a virus that can transport genes into cells. As it turned out, viruses were too small to carry that gene. So Sweeney began searching for a smaller gene that would fit inside a virus and at least mimic dystrophin. He settled on a gene that produces insulin-like growth factor (IGF-I), a powerful hormone that drives muscle growth and repair.
