Ultragenyx Announces U.S. FDA Acceptance of BLA Resubmission for UX111 AAV Gene Therapy to Treat Sanfilippo Syndrome Type A (MPS IIIA)

Q: Does the UX111 BLA include long-term data for Sanfilippo syndrome Type A (RARE)?

Yes. According to the company, the BLA includes up to 8 years of follow-up showing durable clinical improvement versus natural history. The filing also includes multiple supportive biomarker analyses and safety data.

Q: What regulatory status does UX111 hold as of April 2026 for RARE shareholders?

UX111 has Priority Review status and an FDA PDUFA action date set for September 19, 2026 . According to the company, the resubmitted BLA is under active FDA review following prior late-cycle interactions.

Rhea-AI Impact

(High)

Rhea-AI Sentiment

(Positive)

Rhea-AI Summary

Ultragenyx (NASDAQ: RARE) announced the U.S. FDA has accepted the resubmitted BLA for UX111 (rebisufligene etisparvovec) AAV9 gene therapy for Sanfilippo syndrome Type A (MPS IIIA). The FDA set a PDUFA action date of September 19, 2026 and previously granted Priority Review in February 2025.

Updated long-term clinical data in the filing show up to 8 years of follow-up with durable clinical improvements versus natural history and supportive biomarker evidence, and the submission reports an acceptable safety profile. If approved, UX111 would be the first therapy for MPS IIIA and be manufactured in the U.S.

Positive

FDA acceptance of UX111 BLA resubmission with a PDUFA date of Sept 19, 2026
Up to 8 years of long-term clinical follow-up showing durable improvement versus natural history
Priority Review previously granted in February 2025

Negative

BLA still under FDA review; approval is not guaranteed before the PDUFA date of Sept 19, 2026

Key Figures

PDUFA action date: September 19, 2026 Follow-up duration: up to 8 years Priority Review grant date: February 2025

3 metrics

PDUFA action date September 19, 2026 FDA review timeline for UX111 BLA

Follow-up duration up to 8 years Long-term UX111 clinical data included in BLA

Priority Review grant date February 2025 FDA granted Priority Review for UX111 BLA

Market Reality Check

Price: $21.42 Vol: Volume 2,308,775 is in li...

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$21.42 Last Close

Volume Volume 2,308,775 is in line with the 20-day average of 2,333,923 (relative volume 0.99). normal

Technical Shares at $21.42 are trading below the 200-day moving average of $28.94 and 49.45% under the 52-week high of $42.37.

Peers on Argus

RARE gained 2.24% while key biotech peers were mixed: TLX -2.01%, XENE -3.16%, N...

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RARE gained 2.24% while key biotech peers were mixed: TLX -2.01%, XENE -3.16%, NAMS +0.61%, SLNO +8.59%, SRRK -1.06%. Movement appears stock-specific rather than a broad sector move.

Historical Context

5 past events · Latest: Mar 30 (Positive)

Pattern 5 events

Date	Event	Sentiment	Move	Catalyst
Mar 30	IND clearance UX016	Positive	-0.4%	FDA cleared IND for UX016 with Phase 1/2 trial planned.
Mar 27	Class action notice	Negative	-0.4%	Class action lawsuit application deadline reminder announced.
Mar 20	Inducement equity grant	Neutral	+2.0%	Inducement RSU grant to new non-executive officers disclosed.
Mar 12	Positive Phase 3 data	Positive	-2.3%	DTX301 Phase 3 showed 18% ammonia reduction vs placebo.
Feb 27	Class action notice	Negative	-1.6%	Additional class action lawsuit application deadline notice.

Pattern Detected

Positive clinical and regulatory updates have sometimes seen negative next-day reactions, while legal headlines aligned with modest declines.

Recent Company History

Over recent months, Ultragenyx reported several key events, including FDA clearance of an IND for UX016 with a planned Phase 1/2 trial enrolling about 24 adults and positive 36-week Phase 3 data for DTX301 showing an 18% ammonia reduction and reduced treatment burden. At the same time, repeated class action lawsuit notices and insider-related equity grants appeared. Today’s FDA acceptance of the UX111 BLA continues a pattern of advancing its gene therapy pipeline amid ongoing legal and governance activity.

Market Pulse Summary

This announcement highlights FDA acceptance of the UX111 BLA with a Priority Review and a defined PD...

Analysis

This announcement highlights FDA acceptance of the UX111 BLA with a Priority Review and a defined PDUFA action date of September 19, 2026, supported by up to 8 years of follow-up data and biomarker evidence. It builds on prior positive updates across Ultragenyx’s gene therapy pipeline. Investors may track upcoming regulatory interactions, additional UX111 data, and how this potential first treatment for Sanfilippo syndrome Type A integrates with the broader portfolio.

Key Terms

biologics license application, aav9 gene therapy, pdufa action date, priority review, +3 more

7 terms

biologics license application regulatory

"has accepted for review the resubmitted Biologics License Application (BLA)"

A biologics license application is a formal request submitted to regulatory authorities seeking approval to market a new biological medicine, such as vaccines or treatments made from living organisms. It is a comprehensive review process that evaluates the safety, effectiveness, and manufacturing quality of the product. For investors, receiving approval signals that a biological therapy can be sold to the public, potentially leading to revenue growth and market success.

aav9 gene therapy medical

"UX111 (rebisufligene etisparvovec) AAV9 gene therapy as a treatment"

AAV9 gene therapy uses a harmless, naturally occurring virus (AAV9) as a delivery vehicle to carry a working copy of a gene into patients’ cells, often targeting muscle and nervous tissue. Think of it as a microscopic mail carrier delivering an instruction manual so broken cells can produce a missing protein; for investors, it matters because such one-time treatments can command high prices, carry big development and regulatory risks, and can significantly affect a developer’s future revenue and valuation.

pdufa action date regulatory

"The FDA set a Prescription Drug User Fee Act (PDUFA) action date of September 19, 2026."

A PDUFA action date is the deadline the U.S. Food and Drug Administration sets for completing its review of a drug or biologic application under the Prescription Drug User Fee Act. Think of it as a project completion date for a new medicine: the agency’s decision by that date — approval, rejection, or a request for more data — can quickly change a company’s revenue prospects, risk profile, and stock value, so investors monitor it closely.

priority review regulatory

"The FDA granted the UX111 BLA Priority Review in February 2025."

Priority review is a regulatory fast-track that shortens the time an agency spends evaluating a drug, vaccine or medical device application so a decision comes sooner than normal. For investors, it matters because a faster review is like an express lane to market: it can speed revenue potential and reduce regulatory uncertainty, but it does not guarantee approval and still requires the product to meet safety and effectiveness standards.

biomarker medical

"and that the biomarker data provide additional supportive evidence."

A biomarker is a measurable indicator found in the body, such as in blood or tissues, that provides information about health, disease, or how the body responds to treatment. For investors, biomarkers can signal the potential success or risk of medical products or therapies, influencing the value of related companies and industry trends. They act like signals or clues that help assess the progress of medical advancements and their market impact.

neurodegeneration medical

"a rare disease affecting young children that leads to progressive, irreversible neurodegeneration"

Neurodegeneration is the gradual damage and loss of nerve cells in the brain and nervous system, producing symptoms such as memory decline, impaired movement, or thinking problems. Think of it like electrical wiring in a house slowly fraying, which undermines how the system runs. For investors it matters because it drives demand for diagnostics, treatments and long-term care, influences regulatory risk and trial outcomes, and can significantly affect the value of health-care and biotech companies.

sanfilippo syndrome type a medical

"therapy for the treatment of Sanfilippo syndrome Type A, a rare disease"

A severe inherited childhood disease caused by lack of an enzyme needed to break down certain sugars, leading to toxic buildup that destroys brain and body tissue over time. Imagine a household trash system that stops working and garbage piles up, eventually overwhelming the home; similarly, cells are damaged leading to developmental decline and shortened lifespan. For investors, it matters because drug research, clinical trials, and potential therapies for this rare condition can drive biotech valuation, regulatory milestones, and partnerships.

AI-generated analysis. Not financial advice.

04/02/2026 - 08:30 AM

If approved, UX111 will be the first approved therapy for the treatment of Sanfilippo syndrome Type A, a rare disease affecting young children that leads to progressive, irreversible neurodegeneration and early death

PDUFA action date set for September 19, 2026

NOVATO, Calif., April 02, 2026 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) today announced the U.S. Food and Drug Administration (FDA or the Agency) has accepted for review the resubmitted Biologics License Application (BLA) seeking accelerated approval for UX111 (rebisufligene etisparvovec) AAV9 gene therapy as a treatment for patients with Sanfilippo syndrome Type A (MPS IIIA). The FDA set a Prescription Drug User Fee Act (PDUFA) action date of September 19, 2026.

“The FDA’s acceptance of the BLA for UX111 brings us closer to the possibility of a first-ever therapy for Sanfilippo syndrome Type A—a milestone that we recognize cannot come soon enough for families facing this devastating diagnosis,” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx. “We appreciate the FDA’s prompt acceptance of the resubmission and look forward to working with the Agency throughout its review in order to bring this treatment option to the Sanfilippo syndrome community as quickly as possible.”

During its prior late-cycle review, the FDA acknowledged that the neurodevelopmental outcome data are robust and that the biomarker data provide additional supportive evidence. The updated long-term clinical data included in the BLA and presented at WORLDSymposium™ 2026 represent up to 8 years of follow-up and show further clinical improvement relative to the decline observed in natural history, and a durable treatment effect across clinical evaluations and multiple biomarkers, while maintaining an acceptable safety profile.

The FDA granted the UX111 BLA Priority Review in February 2025. If approved, UX111 will be manufactured entirely within the U.S., at Andelyn Biosciences in Columbus, Ohio and the Ultragenyx gene therapy manufacturing facility in Bedford, Massachusetts.

About UX111 (rebisufligene etisparvovec)
UX111 (rebisufligene etisparvovec) is a novel in vivo AAV9 gene therapy in Phase 1/2/3 development for Sanfilippo syndrome Type A (MPS IIIA), a rare fatal lysosomal storage disease with no approved treatment that primarily affects the brain. The therapy is designed to address the underlying sulfamidase (SGSH) enzyme deficiency responsible for abnormal accumulation of heparan sulfate (HS), a glycosaminoglycan, in the brain that results in progressive cell damage and neurodegeneration. UX111 is dosed in a one-time intravenous infusion using a self-complementary AAV9 vector to deliver a functional copy of the SGSH gene to cells. These transduced cells then secrete the functional enzyme into the tissue fluid where it can be taken up by surrounding neurons and other cells. The enzyme is taken up efficiently into other cells and is then routed to the lysosome where it can reduce the accumulation of the HS and prevent the progression of lysosomal storage and consequential injury that occurs in untreated patients. The product was originally developed by Abeona Therapeutics and transferred to Ultragenyx to complete development. The UX111 program has received Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations in the U.S., and PRIME and Orphan medicinal product designations in the EU.

About Sanfilippo Syndrome Type A (MPS IIIA)
Sanfilippo syndrome Type A (MPS IIIA) is a rare, fatal lysosomal storage disease with no approved treatment that primarily affects the brain and is characterized by rapid neurodegeneration, with onset in early childhood. Children with MPS IIIA present with global developmental delay, which eventually leads to progressive cognitive, language and motor decline, behavioral abnormalities and early death. MPS IIIA is estimated to affect approximately 3,000 to 5,000 patients in commercially accessible geographies, with a median life expectancy of 15 years. MPS IIIA is caused by biallelic pathogenic variants in the SGSH gene that lead to a deficiency in the sulfamidase (SGSH) enzyme responsible for breaking down heparan sulfate (HS), a glycosaminoglycan, which accumulates in cells throughout the body, resulting in the observed rapid neurodegeneration that is associated with the disorder.

About Ultragenyx
Ultragenyx is a biopharmaceutical company committed to bringing novel products to patients for the treatment of serious rare and ultra-rare genetic diseases. The company has built a diverse portfolio of approved therapies and product candidates aimed at addressing diseases with high unmet medical need and clear biology for treatment, for which there are typically no approved therapies treating the underlying disease.

The company is led by a management team experienced in the development and commercialization of rare disease therapeutics. Ultragenyx’s strategy is predicated upon time- and cost-efficient drug development, with the goal of delivering safe and effective therapies to patients with the utmost urgency.

For more information on Ultragenyx, please visit the company's website at: www.ultragenyx.com.

Forward-Looking Statements and Use of Digital Media
Except for the historical information contained herein, the matters set forth in this press release, including statements related to the development, regulatory status, review, timing and potential approval of UX111 (rebisufligene etisparvovec), including the anticipated PDUFA action date, the potential for accelerated approval, the outcome of the FDA’s review of the resubmitted Biologics License Application (BLA), the timing and outcome of any regulatory inspections, the sufficiency of clinical, biomarker and long‑term follow‑up data to support regulatory approval, expectations regarding the safety, tolerability and durability of UX111, manufacturing readiness and capabilities, including at third‑party and company‑owned manufacturing facilities, and the potential availability and commercial launch of UX111, are forward‑looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995.

Such forward‑looking statements involve substantial risks and uncertainties that could cause actual results to differ materially from those expressed or implied by the forward‑looking statements. These risks and uncertainties include, among others, the uncertainty and unpredictability inherent in clinical drug development and the regulatory review and approval process; the possibility that the FDA may not accept or agree that the submitted data are sufficient to support accelerated or full approval of UX111; the risk that additional data, analyses or studies may be required; the timing, scope and outcome of regulatory inspections; risks related to the manufacture of UX111, including reliance on third‑party manufacturers and the Company’s limited experience operating its own manufacturing facilities; the ability of the Company and its manufacturing partners to comply with regulatory requirements; potential safety or tolerability issues; competition from other therapies or products; smaller than anticipated market opportunities; and other risks related to the Company’s ability to fund operations, future operating results and financial performance.

For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to the business of Ultragenyx in general, see Ultragenyx's Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 18, 2026, and its subsequent periodic reports filed with the SEC.

In addition to its SEC filings, press releases and public conference calls, Ultragenyx uses its investor relations website and social media outlets to publish important information about the company, including information that may be deemed material to investors, and to comply with its disclosure obligations under Regulation FD. Financial and other information about Ultragenyx is routinely posted and is accessible on Ultragenyx’s Investor Relations website (https://ir.ultragenyx.com/) and LinkedIn website (https://www.linkedin.com/company/ultragenyx-pharmaceutical-inc-/).

Ultragenyx Contacts

Investors
Joshua Higa
ir@ultragenyx.com

Media
Jess Rowlands
media@ultragenyx.com

FAQ

What did Ultragenyx announce about UX111 and the FDA on April 2, 2026 (RARE)?

The company announced FDA acceptance of the UX111 BLA resubmission with a PDUFA date of September 19, 2026. According to the company, the resubmission includes updated long-term clinical and biomarker data supporting potential accelerated approval.

Does the UX111 BLA include long-term data for Sanfilippo syndrome Type A (RARE)?

Yes. According to the company, the BLA includes up to 8 years of follow-up showing durable clinical improvement versus natural history. The filing also includes multiple supportive biomarker analyses and safety data.

What regulatory status does UX111 hold as of April 2026 for RARE shareholders?

UX111 has Priority Review status and an FDA PDUFA action date set for September 19, 2026. According to the company, the resubmitted BLA is under active FDA review following prior late-cycle interactions.

If approved, where would Ultragenyx manufacture UX111 for the U.S. market (RARE)?

If approved, UX111 would be manufactured entirely in the U.S. at Andelyn Biosciences in Columbus, Ohio and Ultragenyx's gene therapy facility in Bedford, Massachusetts. According to the company, both sites are designated for production.

What clinical benefits did Ultragenyx report for UX111 in the BLA resubmission (RARE)?

The company reports durable treatment effects across clinical evaluations and biomarkers, plus further improvement relative to natural history. According to the company, these data were updated and presented with up to 8 years of follow-up.

What does the PDUFA date of September 19, 2026 mean for UX111 investors (RARE)?

The PDUFA date sets the FDA's target to complete action on the BLA by September 19, 2026. According to the company, this date represents the regulatory timeline but does not guarantee approval or the specific outcome.

Ultragenyx Announces U.S. FDA Acceptance of BLA Resubmission for UX111 AAV Gene Therapy to Treat Sanfilippo Syndrome Type A (MPS IIIA)