On Jan. 8, 2020, as I was parking my car, I got a long-awaited phone call from one of my son’s doctors. She informed me that our 7-month-old son, Eliot, had Duchenne muscular dystrophy, a fatal neuromuscular disease.

I can still remember the way the Los Angeles winter sunlight hit the dashboard. I can see my neighbor walking up her steps with groceries, a leaf falling, oblivious to the devastation below. “Life changes in an instant,” Joan Didion wrote. “The ordinary instant.” Our son had a fatal illness. He would die before us.

D.M.D. prevents the production of dystrophin, a protein needed to protect and repair muscle cells. It is caused by a genetic mutation on the X chromosome, thus the disease almost exclusively affects boys (one in 3,300). Over time, children with D.M.D. lose muscle mass and thus the ability to do basic things like run and walk. Eventually they lose their ability to breathe and they experience heart failure. There is no known cure. While existing treatments have helped extend the life span of sufferers they mainly focus on managing symptoms.

In my search for answers for how to save my son, I contacted Dr. Jerry Mendell, a now-retired neurologist at Nationwide Children’s Hospital in Columbus, Ohio, who was running clinical trials for an experimental gene therapy he developed to enable dystrophin production in boys with D.M.D. The treatment, now known as Elevidys, offered the prospect of not merely managing symptoms, but slowing the disease’s progression or even stopping it in its tracks — and potentially, for the first time in the history of this terrible disease, allowing boys with D.M.D. a chance to thrive.

Since I had that first conversation with Dr. Mendell (also a senior adviser for Sarepta, the maker of Elevidys), clinical trials for the gene therapy have had their ups and downs, and some adverse effects have also been reported. But in June 2023, based on a two-part clinical trial, the Food and Drug Administration granted accelerated approval for the treatment for 4- to 5-year-olds who do not have other disqualifying conditions. The F.D.A.’s approval was contingent on continuing trials showing evidence of improved motor function, which had not yet been established.

Before Eliot received his treatment, he had difficulty going up stairs. He complained about being tired after walking only a block or two, even on Halloween when candy ought to have motivated him. Hopping on one foot, a milestone for a 4-year-old, was impossible.