Duchenne muscular dystrophy (DMD) is caused mostly by internal deletions in the 
gene for dystrophin, a protein essential for maintaining muscle cell membrane 
integrity. These deletions abrogate the reading frame and the lack of dystrophin 
results in progressive muscle deterioration. DMD patients experience progressive 
loss of ambulation, followed by a need for assisted ventilation, and eventual 
death in mid-twenties. By the method of exon skipping in dystrophin pre-mRNA the 
reading frame is restored and the internally deleted but functional dystrophin 
is produced. Two oligonucleotide drugs that induce desired exon skipping are 
currently in advanced clinical trials.