---
schema_version: "secwatch.filing_event.v1"
accession: "0001193125-26-103167"
form_type: "8-K"
ticker: "RARE"
cik: "0001515673"
company_name: "Ultragenyx Pharmaceutical Inc."
filed_at: "2026-03-12T23:59:59+00:00"
generated_at: "2026-05-15T13:16:19.437425+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# Ultragenyx DTX301 Phase 3 meets primary endpoint: 18% ammonia AUC reduction (p=0.018) in OTC deficiency

## Summary
- DTX301-treated patients (n=18) showed 18% reduction in 24-hour plasma ammonia AUC vs placebo (n=19) at Week 36 (p=0.018).
- 8 of 9 patients with abnormal baseline ammonia reached normal levels; treated patients maintained normal ammonia despite 27% mean reduction in scavenger meds.
- 71% of treated patients reported much improvement on PGIC vs 0% for placebo at Week 24.
- One SAE of acute hepatitis (resolved with steroids); 5 hyperammonemic crises in placebo (1 death) vs 1 in treated (no deaths).
- Study continues to second primary endpoint on treatment burden; data expected H1 2027.

## SEC filing metadata
- accession: 0001193125-26-103167
- form_type: 8-K
- ticker: RARE
- cik: 0001515673
- company_name: Ultragenyx Pharmaceutical Inc.
- filed_at: 2026-03-12T23:59:59+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/1515673/000119312526103167/0001193125-26-103167-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1515673/000119312526103167/rare-20260312.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001193125-26-103167
- JSON: https://secwatch.observer/filing/0001193125-26-103167.json
- Plain text: https://secwatch.observer/filing/0001193125-26-103167.txt

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