Fayuvi (UX111) by Ultragenyx: status and timeline

Fayuvi (UX111)

Halt brain decline in children with Sanfilippo syndrome type A, who otherwise lose speech, cognition and mobility and rarely live past their teens.

DeployStage 4 of 5

FDA-approved Sep 2026, first treatment for MPS IIIA; shipping to qualified centres within 30-60 days.

Updated 24d agoChecked 11 Oct0 updates this week

Milestones

Next · First commercial treatments at qualified centres

Licensed from Abeona Therapeutics2022Complete.
BLA accepted with priority reviewFeb 2025Complete.
FDA complete response letter (manufacturing, more data)11 Jul 2025Complete.
BLA resubmitted with up to 8 years of follow-up30 Jan 2026Complete.
FDA approval, first MPS IIIA treatment17 Sep 2026+13 mo~~originally 18 Aug 2025~~Complete.
First commercial treatments at qualified centresTarget Q4 2026Current milestone.

Most important updates

Upcoming

Q4 2026First commercial treatments at qualified centres (next)

Current obstacles

Best only if given earlyIt is approved for children whose development is still largely intact; damage already done is not reversed, so diagnosis must come early.
Price and accessAt $3.95M per patient, payers and treatment centres must be lined up one case at a time.

Physics limits

One shot onlyThe body makes antibodies against the AAV shell after a dose, so the therapy cannot be safely repeated if the effect fades, and people with prior AAV antibodies may not qualify.
Small cargoAAV holds only about 4.7 thousand DNA letters. That fits a gene like SGSH but rules out many larger genes without splitting tricks.
Reaching every brain cellEven brain-seeking AAV9 reaches only part of the brain's cells from the blood, which caps how much enzyme can be restored.

How it works

4 parts

Cause

A missing enzyme

Children lack sulfamidase, so a sugar called heparan sulfate piles up in cells and slowly destroys the brain.

Delivery

AAV9 crosses into the brain

AAV9 is a virus shell able to pass from blood into the brain. It carries the healthy SGSH gene in a single IV infusion.

Effect

Cells make the enzyme again

Treated cells make sulfamidase again; the median drop in spinal-fluid heparan sulfate was about 64%, and 4 in 5 patients saw at least a halving.

Safety

Steroids calm the liver

The main side effect is raised liver enzymes, so patients get preventive corticosteroids around dosing.

Spec sheet

Spec	Fayuvi (UX111)
US wholesale price	$3.95M one-time^R (reported)
Trial patients analysed	27 (17 younger, 10 older)^R (reported)
Spinal-fluid heparan sulfate drop	Median 64%^R (reported)
Longest follow-up	8.5 years^R (reported)

^R reported by the company

Update log

2 updates

Thu 17 Sep

Major: FDA approves Fayuvi, the first treatment for Sanfilippo syndrome type A, at $3.95M per patientPressRegulatory

Fri 11 Jul 2025

Major: FDA issues complete response letter for UX111, citing manufacturing and facility observationsPressRegulatory

About Ultragenyx

The team behind Fayuvi (UX111)

Ultragenyx

Rare-disease gene therapies and medicines

Ultragenyx develops medicines for rare genetic diseases. In 2026 it won US approval for two one-time gene therapies: Genglycos for glycogen storage disease type Ia and Fayuvi, the first treatment for Sanfilippo syndrome type A.

Two AAV gene therapies approved in 2026: Genglycos (Aug) and Fayuvi (Sep), each earning a priority review voucher.
Sales come mostly from Crysvita; 2026 revenue guidance is $730-760M, with profit targeted for 2027.
Setbacks: setrusumab missed its main goal in two Phase 3 bone trials (late 2025), and its Angelman drug failed Phase 3 in Sep 2026.

Company profile →

Founded: 201016 yrs
Headquarters: United States
Status: Public
Listed: RARENasdaq
Valuation: public
Staff: ~1,371Jan 2025
Works in: BiotechGene editing & therapy
Coverage: 2 programs · 4 updateslatest 24d agochecked 11 Oct
Partners: Abeona TherapeuticsRegeneron Pharmaceuticals
Suppliers: Andelyn Biosciences
People: Emil KakkisFounder, President & CEOEric CrombezChief Medical Officer & EVPHoward HornEVP, Chief Financial Officer

Spec

Fayuvi (UX111)

US wholesale price

$3.95M one-time^R (reported)

Trial patients analysed

27 (17 younger, 10 older)^R (reported)

Spinal-fluid heparan sulfate drop

Median 64%^R (reported)

Longest follow-up

8.5 years^R (reported)