Shares of Sarepta Therapeutics (SRPT) dropped in morning trading following a report that said that the company had halted treatment at sites in the United Kingdom testing its Duchenne muscular dystrophy drug golodirsen due to "one serious adverse event" that could be related to the drug.

TRIAL HALT: According to news analysis service EP Vantage, Sarepta has temporarily halted treatment at U.K. sites in a clinical trial of golodirsen, an investigational therapy for Duchenne muscular dystrophy in boys with the gene that is amenable for skipping Exon 53, following "one serious adverse event that could possibly be related to the investigational drug product." EP Vantage said it learned of the halt after seeing posts on Facebook from a parent of a child enrolled in the trial. According to the parent, the trial was halted due to an occurrence of rhabdomyolysis, a condition in which damaged skeletal muscle tissue breaks down rapidly. Sarepta confirmed that the Medicines and Healthcare products Regulatory Agency, or MHRA, ordered dosing to be halted at its four centers in the U.K. because of "U.K.-specific stopping rules," and added that safety data from all patients in the ESSENCE study have been reviewed by an independent monitoring committee, which deemed that dosing could continue for all subjects.

PATIENT RESTARTED WITH NO FURTHER ISSUES: STAT's Adam Feuerstein tweeted this morning that "Only thing I'd add, based on my calls, is that the patient re-started golodirsen in the study w/ no further problems." He added that "Folks calling out $SRPT CEO Doug Ingram for lack of transparency after he ripped $SLDB for same. Valid criticism." According to reports, Solid Biosciences (SLDB) failed to disclose some negative issues related to its work on its own DMD treatment. In its IPO filing, Solid said testing of SGT-001 had been partially suspended since November. While the partial clinical hold has kept Solid from administering a high dose of the gene therapy, it is permitted to continue testing a lower dose.

WHAT'S NOTABLE: In September, Sarepta said that in a Phase 1/2 trial in Europe that enrolled 25 boys with DMD, there was a 100% response rate with golodirsen "demonstrating proof of mechanism."

ANALYSTS DOWNPLAY ISSUE: JPMorgan analyst Anupam Rama kept an Overweight rating on Sarepta and said downside in shares this morning is overdone as he does not view the update on the company's ESSENCE trial as a major setback, noting the safety board has suggested the study can continue recruitment. Piper Jaffray analyst Edward Tenthoff reiterated an Overweight rating and $60 price target on Sarepta, and said he is awaiting further clarity on the trial halt before making adjustments. He sees Exondys51 sales of $152M in 2017, at the high end of the $150M-$155M guidance.

PRICE ACTION: In late morning trading, shares of Sarepta Therapeutics are down over 8% to $52.50.