REGENXBIO Inc. (RGNX) on Wednesday announced that the U.S. Food and Drug Administration (FDA) has placed a clinical hold on its investigational gene therapy, RGX-111, for the treatment of Mucopolysaccharidosis Type I, also known as Hurler syndrome, after a potential serious adverse event was traced to a 5-year-old participant.
In addition, the FDA also placed a clinical hold on RGX-121 for the treatment of MPS II (Hunter Syndrome), citing similarities in product, study populations, and risk profiles across the clinical studies.
Following the news, shares are down over 20% at $10.73.
This clinical hold follows preliminary analysis of a single case of neoplasm or intraventricular CNS tumour in a participant treated in its Phase I/II study.
The neoplasm case was detected during a routine brain MRI in a five-year-old participant who had received intracisternal RGX-111 four years earlier, despite showing no symptoms.
The resected tumor that underwent preliminary genetic analysis was detected with an AAV vector genome integration event associated with overexpression of a proto-oncogene (PLAG1), which is known to be susceptible to chromosomal rearrangements.
Currently investigation is ongoing to determine if the adverse event ongoing is drug related.
However, causality has not been established, and the participant remains asymptomatic, with positive developmental progress noted by the treating physician.
No further cases of neoplasm have been reported among the nine other participants treated with RGX-111 or the 32 participants treated with RGX-121.
RGX-111 is designed to use the AAV9 vector to deliver the a-l-iduronidase (IDUA) gene to the central nervous system and has received orphan drug product, rare pediatric disease and Fast Track designations from the FDA for Mucopolysaccharidosis Type I.
Mucopolysaccharidosis Type I (MPS I) is a rare autosomal recessive genetic disease caused by a deficiency in the lysosomal enzyme alpha-L-iduronidase, leading to the accumulation of glycosaminoglycans such as heparan sulfate in various tissues. This accumulation can result in cell, tissue, and organ dysfunction, including cognitive impairment and respiratory issues.
RGX-121 is a potential one-time gene therapy for the treatment of boys with MPS II, designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system.
RGX-121 has received Orphan Drug Product, Rare Pediatric Disease, Fast Track and Regenerative Medicine Advanced Therapy designations from the FDA and advanced therapy medicinal products classification from the European Medicines Agency.
MPS II, or Hunter Syndrome, is a rare, X-linked recessive disease caused by a deficiency in the lysosomal enzyme I2S leading to an accumulation of glycosaminoglycans, including heparan sulfate in tissues which ultimately results in cell, tissue, and organ dysfunction, and central nervous system.
"These are separate therapies, and the positive safety profile of RGX-121 in more than 30 patients treated, including those dosed nearly seven years ago, remains unchanged." Curran Simpson, President and CEO of REGENXBIO.
He also added that RGX-121 presents an opportunity to address the urgent, significant unmet medical need in this ultra-rare disease community, and continued delay means continued neurodevelopmental decline in boys with MPS II.
REGENXBIO has not yet received the full clinical hold letter and awaits additional details from the FDA.
RGNX traded between $5.03 and $16.19 over the last 1 year.
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