Regenxbio, a biotechnology company focused on gene therapy development, has announced positive topline and interim functional data from the pivotal phase 3 portion of its phase 1/2/3 AFFINITY DUCHENNE trial evaluating RGX-202, an investigational gene therapy for Duchenne Muscular Dystrophy (DMD).

The trial achieved its primary endpoint with high statistical significance (p<0.0001), with 93 percent of participants achieving at least 10 percent microdystrophin expression at Week 12. The therapy also demonstrated a statistically significant correlation between microdystrophin expression and functional improvement, marking a key milestone in Duchenne research.

Duchenne muscular dystrophy is a rare and progressive genetic disorder characterised by severe muscle weakness and degeneration. The condition affects approximately one in every 3,500 to 5,000 boys born globally each year and currently has limited treatment options.

The pivotal portion of the AFFINITY DUCHENNE trial evaluated RGX-202 in 31 ambulatory boys aged one year and older. Biomarker data from 30 participants showed an average microdystrophin expression of 71.1 percent across all participants and 41.6 percent in older boys above eight years of age. Additionally, 80 percent of participants achieved more than 40 percent microdystrophin expression.

Interim functional results from nine participants aged approximately 5 to 12 years demonstrated improvements in mobility and disease progression measures 1 year after treatment. Patients showed statistically significant improvement in the North Star Ambulatory Assessment (NSAA) as well as timed function tests, including time to stand, 10-meter walk-run and stair climbing performance, compared with external control groups.

Pat Furlong, Founding President of Parent Project for Muscular Dystrophy, described the findings as encouraging for the Duchenne community, noting that families have long awaited therapies capable of altering the course of the disease.

Aravindhan Veerapandiyan, Principal Investigator of the AFFINITY DUCHENNE study at Arkansas Children’s Hospital, said the results demonstrated robust microdystrophin expression alongside a manageable safety profile, offering hope for improved disease management in Duchenne patients.

Steve Pakola, Chief Medical Officer of Regenxbio, stated that RGX-202 is the first gene therapy in development for Duchenne to demonstrate a statistically significant correlation between microdystrophin expression and functional improvement. He added that the therapy’s differentiated construct and manufacturing process may support improved safety and clinical benefit, including in older patients.

The therapy was reported to be well tolerated overall. Two serious adverse events — one case of subacute myocarditis and one case of asymptomatic liver injury — were reported, both of which resolved without long-term complications. Common adverse events included mild or moderate vomiting, fatigue and nausea.

Regenxbio said more than 20 additional participants have already been enrolled in the confirmatory portion of the study, with all 60 patients expected to complete dosing by mid-2026.

The company also noted ongoing discussions with the US Food and Drug Administration (FDA) regarding accelerated approval pathways. According to Regenxbio, the FDA acknowledged the observed correlation between microdystrophin expression and clinical outcomes and indicated openness to externally controlled trials under certain conditions.

Based on the positive data, Regenxbio plans to pursue accelerated approval for RGX-202 and is preparing for a potential commercial launch in 2027. The company is also finalising the design of an international study to support global regulatory submissions.

RGX-202 is designed to address the underlying cause of Duchenne by delivering a novel microdystrophin construct that includes the C-Terminal domain, a feature intended to support muscle protection and durability. The therapy uses an adeno-associated virus (AAV)-based delivery system and combines a proactive immune suppression regimen with a high-purity manufacturing process.