A Study of NNZ-2591 in Pediatric Participants With Phelan-McDermid Syndrome

May 27, 2026 updated by: Neuren Pharmaceuticals Limited

A Phase 3 Randomized, Double-blind, Placebo-controlled Study to Investigate the Efficacy and Safety of Orally Administered NNZ-2591 Compared With Placebo in Pediatric Participants With Phelan-McDermid Syndrome

This Phase 3, randomized, double-blind, parallel-group (2-arm), placebo-controlled, multicenter study will evaluate the efficacy and safety of NNZ-2591 compared to placebo in pediatric participants with Phelan- McDermid Syndrome.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

After providing informed consent/assent, pediatric participants with Phelan-McDermid syndrome ages 3-12 years of age will enter the 4-week Screening Period and undergo assessments for eligibility, baseline characteristics and symptom severity.

Once eligibility is confirmed, participants will be randomized in a 1:1 ratio to receive either orally administered NNZ-2591 or matching placebo during the 13-week Treatment Period. Subsequently, a 2-week safety follow-up period will occur immediately after the completion of the Treatment Period.

Study Type

Interventional

Enrollment (Estimated)

160

Phase

  • Phase 3

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • United States
    • California
      • San Rafael, California, United States, 94903
    • Illinois
      • Chicago, Illinois, United States, 60612
    • Maryland
      • Chevy Chase, Maryland, United States, 20815
    • Massachusetts
      • Brookline, Massachusetts, United States, 02445
      • Lexington, Massachusetts, United States, 02421
    • New York
      • New York, New York, United States, 10029
    • Ohio
      • Cincinnati, Ohio, United States, 45229

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  1. Male or female pediatric participants with Phelan-McDermid syndrome ages 3 to 12 years (inclusive) at the time of signing the informed consent.
  2. Clinical diagnosis of Phelan-McDermid syndrome with a documented disease-causing genetic abnormality of SHANK3.
  3. Body weight ≥ 10 kg at Screening.
  4. Participants with a PMSA-S overall score ≥ 3 at the Screening and Baseline visits.
  5. Not actively undergoing regression or loss of skills.

Exclusion Criteria:

  1. Use of exclusionary medication or unstable treatment regimens of acceptable concomitant medications as required by the protocol.
  2. Current treatment with more than 3 allowable psychotropic medications.
  3. Participants with seizures must be controlled on no more than 2 anticonvulsant medications (not counting rescue medications).
  4. Psychotropic medications or any other medication used for a chronic illness (not including antibiotics, pain relievers, anti-diarrheals, and laxatives) with doses and dosing regimen that have not been stable for at least 4 weeks before Screening. If the treatment was discontinued, the discontinuation must have occurred no fewer than 2 weeks before the start of Screening.
  5. Any intercurrent seizures in the past 6 months and /or more than 1 seizure in the past 12 months. •A single febrile seizure in the 6 months prior to screening is allowable if no rescue medication was required.
  6. Abnormal liver function laboratory results during the Screening period, as defined by the protocol
  7. Abnormal QT interval on Screening ECG as defined by the protocol.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Quadruple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: NNZ-2591 Arm

The total duration of this study for each participant will be up to approximately 17 to 19 weeks.

Participants will be randomized in a 1:1 ratio to receive orally administered NNZ-2591 during the 13-week Treatment Period.
Drug: NNZ-2591
The study drug will be administered twice daily orally.
Placebo Comparator: Placebo Arm

The total duration of this study for each participant will be up to approximately 17 to 19 weeks.

Participants will be randomized in a 1:1 ratio to receive orally administered placebo matching NNZ-2591 during the 13-week Treatment Period.
Drug: Placebo
The study drug will be administered twice daily orally.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Efficacy of NNZ-2591 compared with placebo as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) overall score.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) overall score. The PMSA-C scores range from 1 to 7 with 1 indicating very much improved and 7 indicating very much worse.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in the Vineland Adaptive Behavior Scales-3, Interview version (Vineland-3) receptive communication subdomain raw score.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in the Vineland Adaptive Behavior Scales-3, Interview version (Vineland-3) receptive communication subdomain raw score. A higher raw score for the receptive communication subdomain indicates better adaptive behavior.
Week 13

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) overall score.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) overall score. The CIC scores range from 1 to 7 with 1 indicating very much improved and 7 indicating very much worse.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) domain scores.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) domain scores. The PMSA-C domain scores range from 1 to 7 with 1 indicating very much improved and 7 indicating very much worse.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) domain scores.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) domain scores. The CIC scores range from 1 to 7 with 1 indicating very much improved and 7 indicating very much worse.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in Phelan-McDermid Syndrome Assessment of Severity (PMSA-S) domain scores.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in Phelan-McDermid Syndrome Assessment of Severity (PMSA-S) domain scores. The PMSA-S scores range from 1 to 7 with 1 indicating typical for age, not at all impaired and 7 among the most severely impaired.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in PMSA-S overall score.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in PMSA-S overall score. The PMSA-S scores range from 1 to 7 with 1 indicating typical for age, not at all impaired and 7 among the most severely impaired.
Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in PMS Clinician Domain Specific Rating Scale (PMS-DSRS) scores.
Time Frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in PMS Clinician Domain Specific Rating Scale (PMS-DSRS) scores. The PMS-DSRS scores range from 0 to 4 with 0 indicating Symptom Not Present and 4 indicating Very Severe.
Week 13

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Neuren Pharmaceuticals Limited

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

November 12, 2025

Primary Completion (Estimated)

October 31, 2027

Study Completion (Estimated)

November 15, 2027

Study Registration Dates

First Submitted

November 13, 2025

First Submitted That Met QC Criteria

December 8, 2025

First Posted (Actual)

December 15, 2025

Study Record Updates

Last Update Posted (Actual)

May 29, 2026

Last Update Submitted That Met QC Criteria

May 27, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • NEU-2591-PMS-301

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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