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NCT Number: NCT07593391

An Open-label Study of NNZ-2591 in Pediatric Participants With Phelan-McDermid Syndrome

This Phase 3, open-label extension, multicenter study will evaluate long-term safety, tolerability and efficacy of NNZ-2591 in pediatric participants with Phelan- McDermid Syndrome.

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Key information

Conditions

Phelan-McDermid Syndrome Telomeric 22q13 Monosomy Syndrome

Age range

3 year–12 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 3

Primary location

Neuren PMS-302 Site#111, San Rafael, California, United States

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About this study

After providing informed consent/assent, pediatric participants with Phelan-McDermid syndrome who participated in previous studies (NEU-2591-PMS-301 and NEU-2591-PMS-001) will undergo assessments for eligibility, baseline characteristics and symptom severity. Once eligibility is confirmed, participants will receive orally administered NNZ-2591 during the 52-week Treatment Period. A 2-week safety follow-up period will occur immediately after the completion of the Treatment Period.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Male or female pediatric participants with Phelan-McDermid syndrome ages 3 to 12 years (inclusive) at the time of signing the informed consent for the antecedent study.
  • Participant must have completed all applicable study visits for the antecedent study in which they participated.
  • Body weight ≥ 10 kg at Screening/Baseline.
  • Participants with a PMSA-S overall score ≥ 3 at the Screening and Baseline visits.
  • Not actively undergoing regression or loss of skills.

Exclusion criteria

  • Use of exclusionary medication or unstable treatment regimens of acceptable concomitant medications as required by the protocol.
  • Participants with seizures must be controlled on no more than 2 anticonvulsant medications (not counting rescue medications).
  • 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.
  • 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.
  • Abnormal liver function laboratory results during the Screening period, as defined by the protocol
  • Abnormal QT interval on Screening ECG as defined by the protocol.

Treatment and study plan

NNZ-2591

Drug

The study drug will be administered twice daily orally.

Primary outcomes

  1. Long-term safety and tolerability of NNZ-2591 as assessed by the incidence of adverse events across participants

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Incidence of TEAEs, AESI and SAEs across participants

  2. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline in ECG Heart Rate (bpm)

  3. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Change from Baseline PR Interval (ms QRS interval (ms)

  4. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Change from Baseline in QT interval (ms)

  5. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Change from Baseline in QTcB interval (ms)

  6. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Change from Baseline in QTcF interval (ms)

  7. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.

    Time frame: Baseline through Safety Follow-Up (Month 12)

    Change from Baseline in RR interval (ms)

  8. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline for heart rate (bpm)

  9. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline for respiration rate (breaths per minute)

  10. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline for Temperature (Celsius)

  11. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline for Diastolic Blood Pressure (mm Hg)

  12. Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.

    Time frame: Baseline through Month 12

    Change from Baseline for Systolic Blood Pressure (mm Hg)

  13. Long-term safety and tolerability of NNZ-2591 as incidence of abnormal, clinically significant clinical laboratory parameters events across participants.

    Time frame: Baseline through Month 12

    Incidence of abnormal and clinically significant laboratory parameters

  14. Long-term safety and tolerability of NNZ-2591 as incidence of abnormal, clinically significant physical examination findings across participants.

    Time frame: Baseline through Month 12

    Incidence of abnormal, clinically significant physical examination findings

Secondary outcomes

  1. Efficacy of NNZ-2591 as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) overall score

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 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.

  2. Efficacy of NNZ-2591 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: Months 3 and 12

    Efficacy of NNZ-2591 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.

  3. Efficacy of NNZ-2591 as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) domain scores.

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 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.

  4. Efficacy of NNZ-2591 as measured by the Caregiver Impression of Change (CIC) domain scores.

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 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.

  5. Efficacy of NNZ-2591 as measured by the change from baseline in Phelan-McDermid Syndrome Assessment of Severity (PMSA-S) domain scores.

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 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.

  6. Efficacy of NNZ-2591 as measured by the change from baseline in Phelan-McDermid Syndrome Assessment of Severity (PMSA-S) overall score.

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 as measured by the change from baseline in Phelan-McDermid Syndrome Assessment of Severity (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.

  7. Efficacy of NNZ-2591 as measured by the change from baseline in PMS Clinician Domain Specific Rating Scale (PMS-DSRS) scores.

    Time frame: Months 3 and 12

    Efficacy of NNZ-2591 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.

Study contacts

Contact information is provided by the study sponsor or research team.

Medical Information Lead

CONTACT

[email protected]

231-203-8050

Sponsors and collaborators

Lead sponsor

Neuren Pharmaceuticals Limited

Industry

Registry information

Official study title

A Phase 3 Open-label Extension Study to Investigate the Long-term Safety and Efficacy of Orally Administered NNZ-2591 in Pediatric Participants With Phelan-McDermid Syndrome

Important dates

Study start
2026
Primary completion
2028
Study completion
2028
First posted
May 18, 2026
Registry last updated
Jul 13, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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