An Extension Study to Evaluate the Long-Term Safety and Efficacy of PTC518 in Participants With Huntington's Disease (HD)

Phase 2

• Conditions: Huntington Disease
• Interventions: Drug: PTC518

• Registration Number: NCT06254482
• Lead Sponsor: PTC Therapeutics

Brief Summary

The primary goal of this study is to evaluate the long-term safety and pharmacodynamic effects of PTC518 in participants with HD.

Detailed Description

Participants who completed the Treatment Period in the parent Phase 2a Study PTC518-CNS-002-HD (NCT05358717), fulfilled the enrollment criteria, and chose to enroll in this extension study will undergo baseline evaluations and be assessed for 54 additional months.

All participants will receive active PTC518 in this extension study. Participants who received PTC518 in the parent Study PTC518-CNS-002-HD will continue at the same dose level they received in that study in a blinded fashion (5, 10, or 20 milligrams \[mg\]). Participants who received placebo in the parent Study PTC518-CNS-002-HD will be allocated to a PTC518 dose level according to the same dosing group in which they were previously randomized (5, 10, or 20 mg). The 20 mg dosing arm will be open for randomization only if and when the Data Safety and Monitoring Board from the parent Study PTC518-CNS-002-HD recommends initiating this dosing level based on an unblinded review of safety data from that study.

Study Timeline

• Study Start: 2023-08-25
• Study First Submitted: 2024-02-02
• Study First Submitted QC: 2024-02-02
• Study First Posted: 2024-02-12
• Status Verified: 2025-06
• Last Update Submitted: 2025-07-09
• Last Update Posted: 2025-07-14
• Primary Completion: 2027-06-30
• Study Completion: 2027-07-20

Recruitment & Eligibility

• Status: ENROLLING_BY_INVITATION
• Sex: All
• Target Recruitment: 250

Inclusion Criteria

• Participant who has completed the Treatment Period in Study PTC518-CNS-002-HD.

Exclusion Criteria

• Participants who have not previously completed the Treatment Period in Study PTC518-CNS-002-HD.

Note: Other inclusion and exclusion criteria may apply.

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: PARALLEL

Arm && Interventions

Group	Intervention	Description
PTC518 5 mg	PTC518	Participants will receive PTC518 5 mg tablets once daily orally for 48 months.
PTC518 10 mg	PTC518	Participants will receive PTC518 10 mg tablets once daily orally for 48 months.
PTC518 20 mg	PTC518	Participants will receive PTC518 20 mg tablets once daily orally for 48 months.

Primary Outcome Measures

Name	Time	Method
Number of Participants With Treatment-emergent Adverse Events (TEAEs)	Baseline up to Month 54
Blood Total Huntingtin Protein (tHTT) Levels	Baseline up to Month 52

Secondary Outcome Measures

Name	Time	Method
Change From Baseline in Caudate Volume as Assessed Via Volumetric Magnetic Resonance Imaging (vMRI) at Month 48	Baseline, Month 48
Change From Baseline in Composite Unified Huntington's Disease Rating Scale (cUHDRS) Scores at Month 48	Baseline, Month 48
Cerebrospinal Fluid (CSF) Mutant Huntingtin Protein (mHTT) Levels	Baseline up to Month 48
Blood mHTT Protein Levels	Baseline up to Month 52

Trial Locations

Locations (24)

Monash Health; 🇦🇺 Clayton, Australia

Westmead Hospital; 🇦🇺 Westmead, Australia

Medical University Innsbruck; 🇦🇹 Innsbruck, Austria

The Ottawa Hospital, Parkinson's and Movement Disorders Clinic; 🇨🇦 Ottawa, Canada

Centre Hospitalier Universitaire d'Angers; 🇫🇷 Angers, France

Hôpital Universitaire de Marseille Hôpital de la Timone; 🇫🇷 Marseille, France

Brain and Spine institute Paris; 🇫🇷 Paris, France

Charite University Medicine Berlin; 🇩🇪 Berlin, Germany

Ruhr-Univ. Bochum St. Joseph-Hospital; 🇩🇪 Bochum, Germany

George-Huntington-Institut; 🇩🇪 Münster, Germany

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