I think its been fairly well explained already, but I'm happy to share from a first (well second) hand view. We have two sons with Duchenne Muscular Dystrophy, and our oldest is on a drug trail. Our youngest was too "healthy" to qualify.

Its not one of the gene editing trials, but an anti-inflammatory that shows some promise. He's been on the trial for nearly 3 years now, the first year was double blind. We didn't know if he was getting a placebo or the study medication, and we still don't know, and won't until at least one year after the last boy gets through that first year. This keeps everyone in the trial completely blind for the first year. However, as noted, in this trial (and most of the other DMD trials I've followed), put everyone on the drug after a certain amount of time, assuming the drug is showing its effective and tolerable.

There are a lot of ethical questions around drug trials, but the controls in place try to address those and balance treating people with the condition and determining if the drug is truly effective. Both are priorities, but you can't ignore either one.