---
schema_version: "secwatch.filing_event.v1"
accession: "0000950170-25-109570"
form_type: "8-K"
ticker: "RARE"
cik: "0001515673"
company_name: "Ultragenyx Pharmaceutical Inc."
filed_at: "2025-08-18T23:59:59+00:00"
generated_at: "2026-05-17T11:53:14.944734+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.7
calibrated_materiality_score: 0.7
confidence: "high"
source: SEC EDGAR
---

# Ultragenyx starts rolling BLA submission for DTX401 gene therapy in GSDIa

## Summary
- Initiated rolling BLA submission to FDA for DTX401 AAV gene therapy for Glycogen Storage Disease Type Ia.
- Submitted non-clinical and clinical modules; plans to complete full BLA including CMC module in Q4 2025.
- BLA includes 96-week Phase 3 data showing ~60-64% reduction in daily cornstarch use from baseline.
- Updates address FDA observations from prior UX111 complete response letter related to CMC and manufacturing.

## SEC filing metadata
- accession: 0000950170-25-109570
- form_type: 8-K
- ticker: RARE
- cik: 0001515673
- company_name: Ultragenyx Pharmaceutical Inc.
- filed_at: 2025-08-18T23:59:59+00:00
- event_type: other_material
- sentiment: positive
- materiality_score: 0.7
- calibrated_materiality_score: 0.7
- confidence: high
- sec_items: 8.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1515673/000095017025109570/0000950170-25-109570-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1515673/000095017025109570/rare-20250818.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0000950170-25-109570
- JSON: https://secwatch.observer/filing/0000950170-25-109570.json
- Plain text: https://secwatch.observer/filing/0000950170-25-109570.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.