It doesn’t help to call the disease fatal. It hasn’t killed the child. It is potentially fatal, life-threatening disease. Treatment is available although success is not guaranteed. It may even be a long shot. But it isn’t fatal until the child dies.
I have a friend who is a research geneticist on pediatric diseases. We just had a conversation about this case, and he stated there is no cure for Charlie Gards genetic disease. He is curious about who this doctor is who even offered to try this experimental treatment, because he considers it unethical and malpractice.