• Shares in Sarepta Therapeutics fell sharply Thursday on news a patient in a key Duchenne muscular dystrophy gene therapy trial was hospitalized, spurring Nasdaq to suspend trading for more than three hours.
• The case, reported in a database of adverse events tabulated by the Food and Drug Administration, was initially characterized as rhabdomyolysis, a severe breakdown in muscle fiber for which muscular dystrophy patients are at higher risk.
• Yet Sarepta says the report was a mistake, calling it “erroneous” in a statement issued after a long delay. According to the company, the boy only had elevated enzymes and was not symptomatic for rhabdomyolysis.

Sarepta’s sharp downward slide Thursday is the latest example of reported side effects renewing safety worries which the gene therapy field has yet to shake.

The case in question showed up in the FDA’s Adverse Events Reporting System (FAERS) as having occurred on February 1 in a 7-year-old boy.  While the record indicates Sarepta itself reported it to the FDA on February 14, the company denied it or the study’s principal investigator had submitted to the database.

The FAERS record also notes a “latest manufacturer received date” of June 7.

DMD patients are more susceptible to rhabdomyolysis because the membrane surrounding their muscle fibers is weaker. In addition, inhaled anesthesia gases can trigger the condition.

The boy was enrolled in a small study of Sarepta’s lead gene therapy, called SRP-9001.

After investigating the incident, Sarepta announced that the patient had received an infusion in the clinical trial, and two weeks later was hospitalized because of dark colored urine and elevated creatine kinase levels, but did not otherwise have symptoms of rhabdomyolysis. He was discharged the next day and his creatine kinase levels returned to normal, Sarepta said.

The trial’s safety monitoring board reviewed the incident and recommended the study continue, Sarepta said. The patient is in a placebo-controlled trial, so he may not have received SRP-9001.

The company did not explain how the incident ended up being reported to FAERS, a database of adverse events related to marketed products rather than experimental drugs.

Rhabdomyolysis had once before stirred worries about a Sarepta therapy, occurring in a patient enrolled in a trial of the now-approved Exondys 51 (eteplirsen) after he fell, noted SVB Leerink analyst Joseph Schwartz.

“We believe investors’ gut reaction is ‘shoot first, ask questions later’ as they re-evaluate the safety profile” of all the gene therapies for DMD, Schwartz wrote in an August 8 note to clients.

Indeed, with the company’s market capitalization just shy of $10 billion, much of its valuation relies on the success of pipeline projects like SRP-9001.

Shares fell 15% following the initial report of the hospitalization, wiping away more than $1 billion in valuation, before recovering to close down 7%.