Sanofi's DM1 Gene Therapy SAR446268 Snags Fast Track Designation

The FDA has granted fast track designation to Sanofi’s SAR446268, an investigational adeno-associated virus (AAV) vector-based gene therapy intended to treat noncongenital (juvenile and adult onset) DM1 myotonic dystrophy type 1 (DM1, also known as Steinert's disease).¹

The therapy, which is currently being evaluated in a first-in-human phase 1/2 clinical trial (NCT06844214), is given as a one-time treatment and is intended to silence expression of the DMPK gene through RNA interference. In addition to fast track designation, SAR446268 has previously received orphan drug designations from the FDA and European Medicines Agency.

“By reducing DMPK transcripts, the gene therapy aims to eliminate the abnormal and toxic RNA foci responsible for splicing defects in muscle tissue, thereby restoring normal splicing and improving muscular function,” Sanofi stated in a press release.¹ “This approach has the potential to address key symptoms of the disease, including progressive muscle weakness, difficulty relaxing muscles (myotonia), and effects on multiple body systems including heart, lungs, and endocrine functions.”

The phase 1/2 trial, which launched on July 23, 2025, is expected to enroll 32 patients aged 10 to 50 years. According to the clinicaltrials.gov page, it is currently recruiting at locations in Florida, New York, and Buenos Aires, Argentina. Sanofi noted that it expects to enroll the first patient in the trial before the end of 2025.

According to Sanofi, there are no treatments for DM1 currently available commercially, and SAR446268 is the only investigational therapy currently in clinical development for DM1. DM1 has a prevalence of about 1 in 2,300 people across the globe, and can vary in severity and the age at which it manifests.

Notably, SAR446268 is the second of Sanofi’s investigational gene therapy products to have received fast track designation from the FDA in September 2025.² Earlier this month, Sanofi's gene therapy SAR402663 received fast track designation for the treatment of neovascular age-related macular degeneration, also known as wet AMD.

SAR402663 comprises a onetime intravitreal treatment and is intended to inhibit vascular endothelial growth factor (VEGF) by providing a gene for soluble FLT01. Inhibition of abnormal blood vessel growth, a decrease in vascular leakage, minimization of retina damage, and a lowering of treatment burden are among the intended effects of SAR402663. It is currently being evaluated in a phase 1/2 dose-escalation and expansion clinical trial (NCT06660667) that is expected to enroll 66 patients in total.

“SAR402663 delivers genetic material encoding soluble FLT01 designed to inhibit VEGF...” Sanofi stated in a press release announcing the designation.² “The gene therapy aims to address the underlying disease pathology by inhibiting abnormal blood vessel growth, reducing vascular leakage and minimizing retina damage, while significantly reducing treatment burden through the elimination of frequent intravitreal injections.”

REFERENCES
1. Sanofi’s SAR446268 earns US fast track designation for the treatment of non-congenital myotonic dystrophy type 1. News release. Sanofi. September 23, 2025. Accessed September 26, 2025. https://www.sanofi.com/en/media-room/press-releases/2025/2025-09-23-05-00-00-3154388
2. Sanofi’s SAR402663 earns fast track designation in the US for neovascular age-related macular degeneration. News release. Sanofi. September 11, 2025. Accessed September 26, 2025. https://www.sanofi.com/en/media-room/press-releases/2025/2025-09-11-05-00-00-3148313