Clinical trials thoroughly evaluate gene therapies. Researchers look at safety, or what side effects participants had, for several years after receiving treatment. They also look at whether the therapy is doing what it was designed to do—make the new protein in the right place within the cell. To look inside cells, researchers have to collect a sample. In Duchenne, this is often accomplished with a muscle biopsy. Western blot and immunofluorescence are lab tests researchers use to measure how much of the new protein is being made and where it is in the cells.
Other tests examine whether the treatment is helping to slow or stabilize the disease. In Duchenne, these tests measure muscle function, like the NSAA (North Star Ambulatory Assessment), PUL (Performance of Upper Limb), and timed function tests like the 6-minute walk test. These tests are given several times before and after treatment with gene therapy. Results are compared over time to track whether motor skills got better, stayed the same, or got worse. They’re also compared to results from those who had no treatment to show if and how well the treatment works overall.