What are the types of mutation in the DMD gene? The dystrophin gene is made up of 79 active pieces of DNA (called ‘exons’). All 79 pieces are joined together in a sequence and communicate the genetic information needed to make the dystrophin protein. How can this cause DMD? Three different types of changes can prevent dystrophin being made, or cause an insufficient amount to be made: 1. Deletions of one or more whole exons – this is the most common type of mutation and is the cause of around 70% of cases of Duchenne. 2. Duplications (additions) of whole exons – this type of mutation is the cause of around 10% of cases of Duchenne. 3. Other small changes in parts of the genetic code, for example point mutations – this type of mutation is the cause of around 20% of cases of Duchenne. Currently, clinical trials are being conducted into ‘gene therapy’, to investigate how to create a working dystrophin gene. If you would like more information on how gene therapy can benefit patients with DMD, please click here.