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SRPT > 38% dystrophin expression...

A Gene Therapy Appears To Replace Missing Protein In Muscular Dystrophy Patients

https://www.forbes.com/sites/matthewherper/2018/06/19/a-gene-therapy-appears-to-replace-missing-protein-in-muscular-dystrophy-patients/#65b69f3e5225

Sarepta's marketed drug, Exondys 51, was approved based on data that it increased levels of dystrophin in patients with a particular type of mutation in the dystrophin gene by much less than 1%, measured with western blot. A May analyst note from Nomura Instinet, an investment bank, predicted the gene therapy would lead to dystrophin levels of 5% to 10% of normal.

The actual western blot number: 38.2% of normal, using Sarepta's western blot method, and 53.7% based on a method developed at Nationwide Children's that corrects for readings in fat and scar tissue. In other words, quadruple the best case.

But gene therapy experts pointed to other data points as more interesting than the ones that Wall Street has fixated on. For instance, boys (for genetic reasons, they're all boys) with Duchenne have high levels of creatinine kinase, an enzyme involved in the destruction of muscle. In the study, the three boys who have been followed for at least two months saw levels of creatinine kinase drop 87% from about 30,000 units per liter.

Then there are the videos. In one shown to me via a webcast, a boy initially climbed stairs one at a time, slowly. Some time after treatment, he bounded up them. Mendell, the lead investigator, asserted that improvements like that don't happen.

Outside researchers were more cautious. Xiao Xiao, a professor at professor at the University of California's Eshelman School of Pharmacy and co-inventor of the Pfizer gene therapy, worried that other issues like changes in steroid treatment could lead to changes in creatinine kinase, for instance. He was nonetheless excited by the results. "I think gene therapy now is coming back after all these years of technology improvement," he said. He would receive royalties if the Pfizer treatment reaches the market.