There are a number of clinical trials underway in DMD that are targeted to certain types of mutations. Genetic testing is important to understand whether your boy is eligible to participate in these trials. To help doctors find the boys who might be eligible, you should register in a patient registry.
The most important question you need to have answered is whether the genetic testing performed was up to currently accepted standards, allowing the exact mutation to be defined. If it was not, then further testing might be required. You should discuss this with your doctor. The exact mutation is also needed to register with one of the DMD registries. You can find details of the kinds of tests that might be done and how effective they are at detecting the absolute detail of the mutation in the main document.
All of the national patient registries for DMD across the world are listed at: www.treat-nmd.eu/patientregistries.
Please see this website for more details.
Information based on consensus statement (published in January 2010)