7. Example - Gene therapy for Duchenne muscular dystrophy
Gene therapy trials for Duchenne muscular dystrophy (DMD) began in 2002. This is a recessive X-linked disease in which muscles gradually degenerate. This occurs throughout the body, but it is the degeneration of heart muscle and respiratory muscles that is generally fatal. The disease is caused by a mutation in the DYSTROPHIN gene, which encodes the protein of the same name. The DYSTROPHIN protein is responsible for linking muscle fibres together and gives muscles strength. Mutations in this gene cause structural instability of muscle fibres and lead to muscle wasting. In DMD, the type of mutation is called ‘loss-of-function’ because the protein the body can produce does not work properly. The prognosis is very poor, with an average life expectancy of only 25 years.
Phase 1 gene therapy trials have been recently initiated in a limited number of patients to test the safety and efficacy of injection of viral gene therapy vectors carrying functional DYSTROPHIN genes into the muscles of patients with DMD. Functional improvement has been observed in some individuals, although a high frequency of immune reactions in response to the viral vectors have been reported. These trials are ongoing as of 2014 and the results will surely be of interest as no other treatments exist for this disease.