---
schema_version: "secwatch.filing_event.v1"
accession: "0000950170-24-138250"
form_type: "8-K"
ticker: "RARE"
cik: "0001515673"
company_name: "Ultragenyx Pharmaceutical Inc."
filed_at: "2024-12-19T23:59:59+00:00"
generated_at: "2026-05-29T01:34:13.287821+00:00"
event_type: "regulatory"
sentiment: "positive"
materiality_score: 0.7
calibrated_materiality_score: 0.7
confidence: "high"
source: SEC EDGAR
---

# Ultragenyx submits BLA to FDA for UX111 gene therapy in Sanfilippo syndrome type A

## Summary
- Submitted BLA to FDA seeking accelerated approval for UX111 (AAV gene therapy) in Sanfilippo syndrome type A (MPS IIIA).
- BLA supported by Transpher A study: rapid, sustained CSF heparan sulfate reduction correlated with improved cognitive development vs. natural history.
- Most common adverse events were liver enzyme elevations; majority mild/moderate (Grade 1/2), all resolved.
- In 2024, FDA agreed CSF heparan sulfate can serve as surrogate endpoint for accelerated approval.

## SEC filing metadata
- accession: 0000950170-24-138250
- form_type: 8-K
- ticker: RARE
- cik: 0001515673
- company_name: Ultragenyx Pharmaceutical Inc.
- filed_at: 2024-12-19T23:59:59+00:00
- event_type: regulatory
- 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/1515673/000095017024138250/0000950170-24-138250-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1515673/000095017024138250/rare-20241219.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0000950170-24-138250
- JSON: https://secwatch.observer/filing/0000950170-24-138250.json
- Plain text: https://secwatch.observer/filing/0000950170-24-138250.txt

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