By Manojna Maddipatla

(Reuters) – Shares in Solid Biosciences Inc plunged 71% on Tuesday after a trial testing its gene therapy for a muscle-wasting disorder was halted for the second time in less than two years.

A seven-year-old boy being treated for the muscle-wasting disorder, Duchenne muscular dystrophy (DMD), experienced serious complications such as a decrease in red blood cell count, acute kidney injury and a drop in platelets, the company said.

However, the patient did not show any signs of bleeding, Solid Biosciences said on a conference call. He was one of the three administered a higher dose of the therapy, SGT-001.

Analysts said the side effects seen were similar to those reported by the first patient who was administered a lower dose of the company’s gene therapy, which led to a clinical hold last March.

The trial, which includes boys aged between 4 and 17, was resumed in June last year after the company made changes to the study.

The halt pushes Solid Biosciences further behind Sarepta Therapeutics Inc and Pfizer Inc in the race to develop the first gene therapy for DMD.

The fact that Sarepta has dosed at least 16 patients to date with no clinical holds speaks to the likely superior safety profile of its therapy, RBC Capital Markets analyst Brian Abrahams said.

It is likely that Sarepta’s drug, SRP-9001, will win sole approval and ultimately generate global sales of $4 billion, he added.

Sarepta’s already available treatment for DMD, Exondys 51, brought in total sales of $301 million in 2018.

DMD is a progressive disorder that mainly affects men. It begins to cause symptoms at an early age, first by hampering the ability to walk and later by causing breathing difficulties and heart problems.

People with the condition lack the protein dystrophin needed to keep muscle cells intact.

Solid Biosciences’ SGT-001 is given intravenously to deliver a gene called microdystrophin, which encodes for a version of the dystrophin protein, into patients’ cells.

“Five of the six children dosed in IGNITE DMD (the trial) are doing well and the sixth boy continues to improve,” Solid Biosciences Chief Executive Officer Ilan Ganot said on the call.

The company said the U.S. Food and Drug Administration and the data safety monitoring board have been informed about the latest incident and that it would work with the agency to determine next steps for the program.

(Reporting by Tamara Mathias and Manojna Maddipatla in Bengaluru; Editing by Sriraj Kalluvila)