---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-26-034474"
form_type: "8-K"
ticker: "RARE"
cik: "0001515673"
company_name: "Ultragenyx Pharmaceutical Inc."
filed_at: "2026-02-03T23:59:59+00:00"
generated_at: "2026-05-16T05:18:45.691611+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# Ultragenyx UX111 gene therapy shows significant cognitive benefit in MPS IIIA; BLA resubmitted with PDUFA Q3 2026

## Summary
- Children under 2 treated with UX111 showed +23.2 point improvement in Bayley-III cognitive raw score vs natural history (p<0.0001).
- 81.5% of overall efficacy set achieved ≥50% reduction in CSF heparan sulfate; median reduction 63.98% (p<0.001).
- Functional retention observed: all older children retained communication; 9/10 retained ambulation and self-feeding.
- UX111 well-tolerated with median follow-up 4.8 years; no TMA, myocarditis, DRG toxicity, or malignancy.
- BLA resubmitted to FDA seeking accelerated approval; PDUFA date expected in Q3 2026.

## SEC filing metadata
- accession: 0001193125-26-034474
- form_type: 8-K
- ticker: RARE
- cik: 0001515673
- company_name: Ultragenyx Pharmaceutical Inc.
- filed_at: 2026-02-03T23:59:59+00:00
- event_type: other_material
- sentiment: positive
- materiality_score: 0.85
- calibrated_materiality_score: 0.85
- confidence: high
- sec_items: 8.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1515673/000119312526034474/0001193125-26-034474-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1515673/000119312526034474/rare-20260203.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-26-034474
- JSON: https://secwatch.observer/filing/0001193125-26-034474.json
- Plain text: https://secwatch.observer/filing/0001193125-26-034474.txt

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