Sarepta’s pioneering work with phosphorodiamidate morpholino oligomer (PMO) chemistries is the basis of our exon-skipping therapies.

Our next-generation chemistry is called PPMO because it adds a peptide to the PMO structure, with the goal of increasing cell nuclei penetration, and has the potential to expand our therapeutic portfolio.


Many diseases are caused by a genetic mutation in a particular gene. Most commonly, one or more exons (parts of the gene) are missing, causing errors in the instructions for making a specific protein. This results in the body not being able to produce enough—or any—of that protein. The goal of exon skipping, is to act on the RNA to allow the body to make a version of the missing protein to bypass the mutation.

An Exon Skipping Example

A gene is made up of exons (portions of a gene) that are linked together to provide instructions for making a specific protein.

Each exon connects with its neighboring exons in a specific way. Exon 43, for instance, connects on one side with exon 42 in a specific way and on the other with exon 44, also in a specific way.

If exon 43 is missing, exon 42 cannot connect directly to exon 44 because their connectors don’t fit together, and because they don't fit together the body is unable to read the genetic instructions for making the protein.

exon skipping 1

Skipping Over Exons

By hiding certain exons, we can “skip” their location to link with an exon with the right connector. This would allow for a production of a shortened and potentially functional form of the missing protein.

In this example, the PMO directs the splicing machinery to skip an exon when processing the pre-mRNA. As a result, the alternate mRNA allows for the production of a shorter form of the missing protein. exon skipping 2