[Molecular genetics of Duchenne/Becker muscular dystrophy]

The X-linked gene responsible for Duchenne muscular dystrophy (DMD)/Becker muscular dystrophy (BMD) encodes dystrophin, a high-molecular-weight cytoskeletal protein. The identification of the dystrophin gene through positional cloning, and the subsequent description of its protein product have opened several new fields of research and genetic diagnosis. Studies in our laboratory revealed that 26 out of 47 (55%) cases of DMD and nine out of 12 (75%) cases of BMD exhibited genomic deletion. The DMD phenotype is associated with mutations that shift the reading frame of the message, whereas the BMD phenotype is associated with mutations that maintain the reading frame. Immunofluorescence microscopy has established dystrophin's distribution on the plasma membrane of muscles. DMD patients demonstrate a lack of dystrophin on their muscle cell membrane, whereas BMD patients produce a limited amount of protein or abnormally sized protein. Extensive studies on dystrophin and the gene may lead to an understanding of the cause for this and may allow development of a rational treatment for DMD to be developed.