What happened

Shares of Solid Biosciences (SLDB 5.38%) were moving 15.9% lower as of 11:29 a.m. EST on Friday. The drop came after Sarepta Therapeutics (SRPT 1.27%) reported disappointing clinical results for experimental gene therapy SRP-9001 in treating rare genetic disease Duchenne muscular dystrophy (DMD). Solid's leading pipeline candidate, SGT-001, is also a gene therapy targeting DMD.

So what

Sarepta's problem was that SRP-9001 didn't meet the primary functional endpoint of its clinical study. That endpoint was a statistically significant improvement in score on the North Star Ambulatory Assessment (NSAA), a scale used to assess the functional motor abilities in children with DMD.

Duchenne muscular dystrophy printed over a bar code with pipettes behind the bar code label

Image source: Getty Images.

Just because SRP-9001 failed in a clinical study doesn't necessarily mean that SGT-001 will. However, Solid's SGT-001 uses the same approach for treating DMD that SRP-9001 does. It transfers microdystrophin, a synthetic version of the dystrophin-producing gene, into the cells of a DMD patient in hopes to restore muscle function. DMD is caused by a mutation in the gene that encodes the protein dystrophin.

Sarepta appears to believe that the randomization process with its clinical study could be the culprit. Patients in the study ages 4 and 5 did achieve statistically significant functional improvement, while those ages 6 and 7 didn't. Sarepta CEO Doug Ingram said that "the randomization process resulted in a significant imbalance in baseline NSAA scores between the active and placebo cohorts of the participants ages 6-7, making the 6-7 age groups non-comparable and likely substantially contributing to the inability to achieve statistical significance."

Now what

It's understandable that Solid Biosciences would be weighed down by Sarepta's news. However, the most important thing for the biotech stock is Solid's own clinical testing. The company plans to resume dose in its phase 1/2 clinical study of SGT-001 soon after the U.S. Food and Drug Administration lifted a clinical hold on the trial in October.