The market approval for Fayuvi, which was rejected in 2025 due to manufacturing problems, comes shortly after Ultragenyx got the FDA nod for its first gene therapy last month.
The FDA has given the go-ahead to Ultragenyx’s rebisufligene etisparvovec—now to be marketed under the brand name Fayuvi—for the treatment of Sanfilippo syndrome type A, an ulta-rare, progressive neurological condition in children.
Fayuvi is the first-ever FDA-approved therapy for the fatal condition, according to a company news release on Thursday afternoon. Sanfilippo syndrome type A causes children to gradually lose cognitive and other developmental abilities, with Ultragenyx’s new therapy indicated for patients with preserved neurodevelopmental function.
The approval represents a comeback for the one-time gene therapy, which was initially rejected in July 2025 due to manufacturing issues.
Ultragenyx expects Fayuvi will be available to ship within 30 to 60 days, with a wholesale acquisition cost of $3.95 million, Jefferies reported in a note on Thursday evening. That would make it one of the most expensive gene therapies of all time, trailing Orchard Therapeutics’ Lenmeldy for pediatric metachromatic leukodystrophy, which costs $4.25 million, according to a BioSpace analysis.
Ultragenyx was up 13% by the end of Thursday’s trading session, hitting $14.50 per share.
Fayuvi is Ultragenyx’s second gene therapy to cross the FDA finish line, behind Genglycos, which was cleared last month for a rare genetic disease called glycogen storage disease type Ia or Von Gierke disease. . Genglycos, also a one-time therapy, is expected to cost $2.7 million.
Also called mucopolysaccharidosis type IIIA, Sanfilippo syndrome type A is a rare and heritable disorder characterized by progressive damage to the brain and nervous system, with treatment options up to this point limited to managing symptoms, according to the FDA’s announcement of Fayuvi’s approval.
Ultragenyx estimates around 3,000 to 5,000 treatable patients in “commercially accessible geographies. With a median life expectancy of around 15 years for patients with the disease, Jefferies expects the high unmet need to facilitate Fayuvi’s uptake. Ultragenyx said they were already receiving requests already for the drug, including outside of the U.S., according to the analyst.
Also going in Ultragenyx’s favor is the company’s existing manufacturing infrastructure, which the firm contended can drive down production costs to “biologics-like levels.” Jefferies projects peak sales of around $250 million for Fayuvi.
Fayuvi was initially developed at Abeona Therapeutics as ABO-102. In 2022, Ultragenyx picked up exclusive licensing rights to the gene therapy, with Abeona on the line to collect up to $30 million in commercial milestones, plus tiered royalties.
The adeno-associated virus gene therapy works by delivering a functional copy of the SGSH gene, which encodes an enzyme that is deficient in Sanfilippo, leading to the buildup of a certain molecule in cells that in turn progressively damage the nervous system. Positive data from the pivotal Phase 1/2/3 Transpher A trial supported Fayuvi’s approval, showing biomarker and cognitive improvements as compared with untreated patients from an external national history control group.
Fayuvi’s approval gives Ultragenyx a second priority review voucher (PRV), adding to the one it got for Genglycos’ approval. Ultragenyx intends to sell these vouchers, which William Blair analysts in a Friday morning note said “will significantly bolster the company’s balance sheet given the market rate for PRVs is ~$200 million.” As of June 30, the biopharma had $436 million in cash, equivalents and marketable securities.
The approval follows a Phase 3 fail in Angelman syndrome earlier this month that
prompted Ultragenyx to “assess its planned operations” and initiate “significant expense reductions.” The biotech reported that its investigational antisense oligonucleotide apazunersen was unable to significantly improve cognition, an update that sent the company’s stock crashing more than 43% at the time.
