Pfizer’s investigational gene therapy for Duchenne muscular dystrophy (DMD) has been granted a fast track designation from the US Food and Drug Administration (FDA).

DMD is a life-threatening X-linked disease caused by mutations in the gene encoding dystrophin, which is required for proper muscle membrane stability and function.

Muscle degeneration progressively worsens with age, with many affected individuals usually succumbing to their disease by the time they are in their late twenties. This rare condition overwhelmingly affects males, and it is estimated that there are 10-12,000 individuals affected by DMD in the US.

According to Pfizer, the fast track designation was based on data from a phase Ib study of the gene therapy that indicated that the intravenous administration was well-tolerated during the infusion period, and dystrophin expression levels were sustained over a 12-month period.

The therapy, PF-06939926, is a recombinant adeno-associated virus serotype 9 (rAAV9) capsid carrying a shortened version of the human dystrophin gene under the control of a human muscle-specific promotor.

“The FDA’s decision to grant our investigational gene therapy PF-06939926 Fast Track designation underscores the urgency to address a significant unmet treatment need for Duchenne muscular dystrophy,” said Brenda Cooperstone, chief development officer, Rare Disease, Pfizer Global Product Development.

“DMD is a devasting condition and patients, and their parents, are waiting desperately for treatment options. We are working to advance our planned phase III programme as quickly as possible,” she added