Pfizer just announced the passing of a patient who was participating in the phase 1b mini-dystrophin gene therapy trial for Duchenne muscular dystrophy (DMD).

The company confirmed that the patient was enrolled in the nonambulatory cohort of the study. Investigations are ongoing to determine the cause of the death, they said in the community letter.

“The safety and well-being of the patients in our clinical trial remains our top priority, and we are committed to sharing more information with the medical and patient community as soon as we can,” the company assured.

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Pfizer is working closely with the independent External Data Monitoring Committee to review the clinical data. The screening and dosing of the trial will be paused until further notice. Moreover, the Investigational New Drug Application was placed on clinical hold by the US Food and Drug Administration.

Read more about DMD overview

“The words to describe the unjust nature of a tragedy like this lay meaningless on the page, they are swallowed up in our throats along with our grief,” Pat Furlong, founding president and chief executive officer of Parent Project Muscular Dystrophy said.

However, she keeps confident that science and gene therapy are the way to move forward in DMD. “We must continue to invest in genetic therapies because of the science and possibilities, but we must do with blinders removed from our hearts and minds.”

Pfizer’s phase 1b mini-dystrophin gene therapy trial 9 (NCT03362502) is evaluating the safety and tolerability of a single intravenous infusion of PF-06939926 in ambulatory and nonambulatory patients with DMD.


Update on Pfizer’s phase 1B open-label mini-dystrophin gene therapy trial for Duchenne. News release. Parent Project Muscular Dystrophy; December 20, 2021.

A study to evaluate the safety and tolerability of PF-06939926 gene therapy in Duchenne muscular dystrophy. December 5, 2017. Updated October 15, 2021. Accessed December 22, 2021.