Duchenne muscular dystrophy: present and future therapy

Abstract

Duchenne muscular dystrophy (DMD) is the second commonest genetic disease in Western populations, occurring in 1 in 4000 live male births/ It is an X-linked disorder, characterized by progressive loss of muscle power and development of joint contractures, which may be associated with intellectual impairment and cardiomyopathy. Progressive respiratory muscle weakness and occasionally cardiomyopathy lead to death in affected boys by their late teens or early twenties. While a relatively small part of paediatric workload, the importance of the condition is two-fold: first, while at present there is no curative treatment, the quality of life of affected boys can be improved considerably by vigorous appropriate management; secondly, the explosion of interest in molecular genetics and possible gene therapy has featured DMD and its milder allelic disorder Becker muscular dystrophy (BMD) as one of the inherited conditions in which the gene has been cloned and has offered itself for manipulation. wide range of tissues including muscle, brain and cardiac muscle. It is absent from DMD muscle, leading to muscle cell necrosis. This forms the basis of the diagnostic features on muscle biopsy: in DMD, dystrophin cannot be identified whereas in BMD, dystrophin is present although in reduced amount or of altered molecular weight. The molecular abnormalities in DMD and BMD are usually intragenic deletions, which can be identified with current laboratory techniques in about 65% of boys. Other abnormalities identified include point mutations and duplications. The position of the deletion with reference to the DNA triplet eodon sequence of bases has been suggested to explain severity of phenotype; for those deletions which leave the reading frame out of frame, a severe phenotype occurs as the genetic message is a nonsense, while an in-frame deletion leads to a milder phenotype such as BMD as dystrophin, albeit a truncated form, is synthesized)