Muscle Restoration In Mice With Duchenne Muscular Dystrophy Demonstrated For The First Time

This genetic flaw causes from 5 to 15 percent (and in a few instances up to 70 percent) of individual cases of most inherited diseases, including DMD, cystic fibrosis, and hemophilia.

The new drug, developed by the South Plainfield, NJ-biotech firm and called PTC124, binds to the ribosome, a cellular component where the genetic code is translated into proteins, one amino acid at a time. The drug allows the ribosome to read through a mistake in the genetic code called a premature stop codon in order to properly make whole proteins.

In DMD, patients are missing dystrophin, a protein that helps keep muscle cells intact. About 15 percent of DMD patients do not make dystrophin because of the mutation. DMD eventually affects all voluntary muscles, as well as heart and breathing muscles.

PTC124 attaches to ribosomes in all cell types within the MD mouse model, overriding the mutation in the dystrophin gene that tells it to halt production of the protein. Instead of stopping, the full-length dystrophin protein is made. The drug enables enough protein to be made to correct defects in the muscle of the DMD mouse, and at the same time the drug does not prevent the ribosome from reading correct "stop" signals in the genetic code to make other necessary proteins.

"Enough dystrophin accumulated in the muscles of the MD mice so that we could no longer find defects in the muscles when we examined them," says Sweeney. "For all intents and purposes the disease was corrected by treatment with PTC124." The drug allowed dystrophin to be made in cells in which it was previously absent, to be delivered to the proper location at the cell membrane, and to induce restoration of muscle function in rodent muscles.

Co-first author Elisabeth Barton, PhD, worked on this project as a postdoctoral fellow in the Sweeney lab, and continued as a collaborator when she became an Assistant Professor in Penn's School of Dental Medicine.

The study was supported in part by the Muscular Dystrophy Association and the Parent Project Muscular Dystrophy. The research appears ahead of print in an advanced online publication of Nature.