Why dystrophin quantification is key in the eteplirsen saga

Eteplirsen, a compound designed to restore dystrophin in patients with Duchenne muscular dystrophy, controversially received approval by the FDA in 2016. Owing to limited clinical data, the approval was based on eteplirsen's effect on dystrophin expression. Now, the dystrophin quantification results have been published, and although low levels of dystrophin expression are shown, the quantification remains debatable.