Dystrophinopathies are progressive hereditary degenerative diseases (often called muscular dystrophies) of skeletal muscles due to an absence or deficiency of the protein dystrophin. Dystrophin and the associated proteins form a complex system that connects the intracellular cytoskeleton to the extracellular matrix. The normalcy of this system is critical for maintaining the integrity of the delicate, elastic muscle membrane (sarcolemma) and the muscle fiber. The responsible gene is located on the short arm of the X chromosome at locus Xp21. It is an extremely large gene, comprising more than 2.5 million base pairs and 79 exons. The dystrophin gene produces several isoforms (alternative forms of a protein) of dystrophin. Seven distinct promoters have been identified, each driving a tissue-specific dystrophin.

The most common mechanisms of mutation are deletions and duplications largely clustered in the "hot spot," a DNA sequence associated with an abnormally high frequency of mutation or recombination, between exons...