---
schema_version: "secwatch.filing_event.v1"
accession: "0000950123-24-003302"
form_type: "8-K"
ticker: "RARE"
cik: "0001515673"
company_name: "Ultragenyx Pharmaceutical Inc."
filed_at: "2024-04-15T23:59:59+00:00"
generated_at: "2026-06-03T22:54:04.609467+00:00"
event_type: "other_material"
sentiment: "positive"
materiality_score: 0.85
calibrated_materiality_score: 0.85
confidence: "high"
source: SEC EDGAR
---

# Ultragenyx reports positive Phase 1/2 GTX-102 data in Angelman syndrome with rapid, sustained improvements

## Summary
- Expansion Cohorts A&B (24 patients) at Day 170 showed clinically meaningful improvements across cognition, behavior, sleep, motor, and communication domains vs natural history.
- Multi-domain responder index (MDRI) net response of +2.0 (p<0.0001) at Day 170; majority of patients achieved +2 to +4 domain improvement.
- Dose-escalation Cohorts 4-7 (15 patients) at Day 758 showed sustained long-term benefit; MDRI net response +2.0 (p=0.0007) at Day 338.
- No unexpected serious adverse events; three patients had mild-moderate lower extremity weakness (resolved, no recurrence on re-dosing).
- FDA notified of safety events; no issues raised or additional actions required; data to be presented at AAN 2024.

## SEC filing metadata
- accession: 0000950123-24-003302
- form_type: 8-K
- ticker: RARE
- cik: 0001515673
- company_name: Ultragenyx Pharmaceutical Inc.
- filed_at: 2024-04-15T23:59:59+00:00
- event_type: other_material
- sentiment: positive
- materiality_score: 0.85
- calibrated_materiality_score: 0.85
- confidence: high
- sec_items: 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1515673/000095012324003302/0000950123-24-003302-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1515673/000095012324003302/rare-20240415.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0000950123-24-003302
- JSON: https://secwatch.observer/filing/0000950123-24-003302.json
- Plain text: https://secwatch.observer/filing/0000950123-24-003302.txt

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