Saturday, June 23, 2018

Eteplirsen for Duchenne Muscular Dystrophy

Eteplirsen is a new drug for treatment of Duchenne muscular dystrophy.  Its brand name is Exondys 51.  Eteplirsen is an antisense morpholino.

Duchenne muscular dystrophy occurs from a mutation of the gene for dystrophin.  Usually this is a deletion of part of the gene.  The dystrophin protein protein reinforces the muscle cell membrane and acts like he wooden frame of the walls of a house.  As muscle cells contract and lengthen during movement, dystrophin reinforces the cell membrane and protects it from damage. Boys and men who have Duchenne muscular dystrophy have no dystrophin or almost no dystrophin in their muscles.  Even a very small amount of dystrophin helps a lot.  This is why males who have Becker muscular dystrophy, and have a reduced amount of function dystrophy have a milder disease that those who have Duchenne muscular dystrophy and have almost none.

The deletion in the gene for dystrophin disrupts the reading frame when the internal cell mechanisms read the gene to make dystrophin.  Every part of the gene past the deletion codes wrong the gene product is no good.  The antisense morpholino results in skipping over the part the gene that is disrupted.  The cell reads the gene correctly before and after the skipped portion. The gene product is a dystrophin molecule that is missing a piece in the middle but is otherwise normal and functional.

About 13 % of boys who have Duchenne muscular  dystrophy have deletion that Exondys 51 can treat.  Antisense morpholinos for other gene deletions are in development.

Further Reading

Annals of Neurology 2016 Paper: Longitudinal effect of eteplirsen versus historical control on ambulation in Duchenne muscular dystrophy
Abstract with link to free full text article

Neurology 2018 Paper: Eteplirsen treatment for Duchenne muscular dystrophy: Exon skipping and dystrophin production

Muscular Dystrophy Association
Search the MDA website for news and information

Sarepta (the pharmaceutical company that makes Exondys 51)
Search the Sarepta website for news and more information

Wikipedia article on morpholinos