Shares of REGENXBIO Inc. suffered a sharp decline on Thursday, dropping approximately 37% to $6.31, even after the biotech firm announced that its experimental gene therapy, RGX-202, successfully met the primary endpoint in a late-stage trial for Duchenne muscular dystrophy (DMD). The sell-off reflected investor concerns over two serious adverse events reported in the study and an uncertain path to regulatory approval.
The stock touched an intraday low of $6.02, with trading volume surging to over 8.6 million shares, far exceeding the typical activity for the small-cap company based in Rockville, Maryland. The market's reaction underscored the high stakes surrounding RGX-202, which is central to REGENXBIO's pipeline and faces competition from Sarepta Therapeutics' Elevidys, the leading Duchenne gene therapy that has been scrutinized after two deaths linked to acute liver failure.
Trial Results and Biomarker Data
REGENXBIO reported that 93% of evaluable patients achieved over 10% microdystrophin expression by week 12 in the pivotal Phase III portion of its AFFINITY DUCHENNE trial. Microdystrophin, a truncated version of the dystrophin protein that is missing or defective in DMD, served as the primary biomarker endpoint. Among 31 ambulatory boys aged at least 1 year, the average microdystrophin expression reached 71.1% in those with biopsy results. For boys over 8, a group typically experiencing functional decline, the figure was 41.6%.
Chief Medical Officer Steve Pakola hailed the link between microdystrophin expression and functional improvements as a “landmark distinction” for Duchenne gene therapy. Principal investigator Aravindhan Veerapandiyan from Arkansas Children’s Hospital described both the expression results and the “manageable safety profile” as encouraging. Pat Furlong, representing Parent Project Muscular Dystrophy, noted that families “cannot wait” for new treatments.
Safety Concerns and Regulatory Hurdles
Despite the positive biomarker data, the trial recorded two serious adverse events that rattled investors. An 8-year-old patient developed subacute myocarditis, an inflammation of the heart muscle, while a 10-year-old showed asymptomatic liver injury. REGENXBIO stated that both incidents resolved within weeks without lasting effects. However, Mani Foroohar at Leerink Partners described the data as a “mixed bag,” highlighting that the adverse events and the FDA’s stance could spark debate.
The company plans to seek accelerated approval from the FDA, a pathway that allows drugs to be approved based on surrogate markers “reasonably likely” to predict clinical benefit. REGENXBIO noted that the FDA has indicated a preference for a randomized controlled trial but has signaled that externally controlled trials might be acceptable if the treatment effect is strong enough. The company targets a potential launch in 2027.
Broader Pipeline and Financial Context
The setback comes amid a challenging period for REGENXBIO’s rare-disease programs. In January, the FDA placed clinical holds on RGX-111 and RGX-121 after a brain tumor emerged in a patient receiving RGX-111. The following month, the agency declined to approve RGX-121 for Hunter syndrome, citing trial design concerns. On Thursday, REGENXBIO announced that the FDA had lifted the partial clinical hold on RGX-121, and the company has appealed the complete response letter for that therapy.
Financially, REGENXBIO reported a net loss of $90.1 million for the first quarter, swinging from net income of $6.1 million a year earlier, as revenue plunged to $6.4 million from $89.0 million. The company’s cash burn and reliance on pipeline success add to investor unease.
Competitive Landscape and Outlook
The Duchenne gene therapy space remains fraught with challenges. Sarepta’s Elevidys, the current standard, has faced safety concerns after two deaths linked to acute liver failure, as reported by Reuters last year. For RGX-202, functional data remain limited—just one year of follow-up from only nine patients—and clinicians outside the trial will seek longer-term evidence on heart, liver, and durability outcomes. The bear case centers on the thin, non-randomized functional readout, which relies on external controls.
REGENXBIO’s stock decline reflects the market’s cautious stance, balancing promising biomarker results against safety signals and regulatory uncertainty. The company’s ability to navigate the FDA’s requirements and deliver robust long-term data will be critical for RGX-202’s future and the company’s valuation.
