What happened

Shares of Solid Biosciences (SLDB 5.38%) are getting hammered today, down by 14% as of 11:54 a.m. EST, after the company released data from two Duchenne muscular dystrophy patients treated with the higher dose of its gene therapy SGT-001.

Unfortunately, there are safety issues with the higher dose, and the results for the two patients that didn't have severe adverse events don't look as promising as results from Sarepta Therapeutics' competing gene therapy.

Doctor examining a boy's leg

Image source: Getty Images.

So what

One of the three patients who were treated at the higher dose had an immune reaction that caused kidney damage, a decrease in red blood cell count, and cardiopulmonary insufficiency. Solid Biosciences noted that the issue has resolved, but the clinical trial remains on a hold by the Food and Drug Administration. To convince the agency to lift the hold, Solid Biosciences will need to figure out what caused the adverse event and have a plan to keep it from happening in the future.

The two other patients had expression of microdystrophin -- the gene transferred in the therapy -- of around 5% of normal for one patient and 17.5% of normal for the other patient. Looking at the muscle fibers, 10%-20% of the fibers had expression in one of the patients and the other patient had expression in 50%-70% of the fibers.

While it's clear SGT-001 is doing something, the results are underwhelming compared to results from the first four patients treated with Sarepta Therapeutics' competing gene therapy, which produced an average expression of 74.3% to 95.8% of normal, depending on which method was used to measure expression. Microdystrophin expression was seen in an average of 81.2% of the fibers.

Now what

With underwhelming data at the highest dose and a safety issue to boot, Solid Biosciences' prospects for SGT-001 aren't looking very promising. Investors looking to buy a biotech working on treatments for Duchenne muscular dystrophy would be better off going with the established leader, Sarepta Therapeutics.