Genglycos (DTX401) by Ultragenyx: status and timeline

Genglycos (DTX401)

Restore the liver enzyme G6Pase-alpha so patients keep blood sugar stable through fasting and need far less cornstarch.

DeployStage 4 of 5

FDA accelerated approval Aug 2026 for patients 8+; a confirmatory 2-year study is required.

Updated 19 Aug 2026Checked 11 Oct0 updates this week

Milestones

Next · Confirmatory study: 50 treated vs 20 controls, 2 years

BLA accepted with priority reviewFeb 2026Complete.
FDA accelerated approval, first gene therapy for GSDIa19 Aug 2026Complete.
Confirmatory study: 50 treated vs 20 controls, 2 yearsNowCurrent milestone.

Most important, last 3 months

FDA grants accelerated approval to Genglycos, the first gene therapy for glycogen storage disease type Ia19 Aug 2026

Current obstacles

Confirming lasting benefitAccelerated approval requires a two-year study and 10-year monitoring to show the effect holds.
Antibodies exclude some patientsPeople with existing antibodies to AAV8 cannot receive it; they serve as the control group in the follow-up study.

Physics limits

Gene copies dilute in growing liversAAV genes sit beside, not inside, the cell's DNA. When liver cells divide, as in growing children, copies are lost and the effect can fade.
Cannot be redosedA first dose triggers lasting antibodies against the AAV shell, so a second infusion would likely be neutralised.

How it works

3 parts

Cause

Liver can't release glucose

A broken G6PC gene means the liver stores sugar but cannot turn it back into blood glucose between meals.

Delivery

AAV8 homes to the liver

An AAV8 virus shell, drawn to liver cells, carries a working G6PC gene in one IV infusion.

Effect

Longer safe fasting

With the enzyme back, the liver can supply glucose again; in Phase 3, treated patients cut daily cornstarch by about 41% versus 10% on placebo.

Spec sheet

Spec	Genglycos (DTX401)
Phase 3 participants	46^R (reported)
Daily cornstarch cut at 48 weeks	41% mean (placebo 10%)^R (reported)
Dose	1.0 x 10^13 GC/kg^R (reported)
Approved ages	8 years and older^R (reported)

^R reported by the company

Update log

1 update

Wed 19 Aug

Major: FDA grants accelerated approval to Genglycos, the first gene therapy for glycogen storage disease type IaFilingRegulatory

About Ultragenyx

The team behind Genglycos (DTX401)

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

Genglycos (DTX401)

Phase 3 participants

46^R (reported)

Daily cornstarch cut at 48 weeks

41% mean (placebo 10%)^R (reported)

Dose

1.0 x 10^13 GC/kg^R (reported)

Approved ages

8 years and older^R (reported)