A Phase 3 interventional study of NNZ-2591 and Placebo in Phelan-McDermid Syndrome, sponsored by Neuren Pharmaceuticals Limited. Recruiting at 18 sites in 2 countries. Open to participants aged 3 Years to 12 Years. Per ClinicalTrials.gov, last updated 2026-09-28.
Sponsored by Neuren Pharmaceuticals Limited · Phase 3, Interventional, and Treatment
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.
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.
Neuren Pharmaceuticals Limited is the lead sponsor of 15 studies on the registry; 2 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
QT and QTc
On an ECG, the QT interval is the time the heart’s lower chambers take to activate electrically and recover in each beat. QTc is that time adjusted for heart rate (QTcF by Fridericia’s formula, QTcB by Bazett’s). Some medicines lengthen it, and a long QTc can raise the risk of a dangerous heart rhythm.
The study may name a correction formula and a limit in milliseconds, often around 450–480.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
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 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.
The study drug will be administered twice daily orally.
Efficacy of NNZ-2591 compared with placebo as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) overall score.
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.
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.
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.
Time frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) overall score.
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.
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.
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.
Time frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the Caregiver Impression of Change (CIC) domain scores.
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.
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.
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.
Time frame: Week 13
Efficacy of NNZ-2591 compared with placebo as measured by the change from baseline in PMSA-S overall score.
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.
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.
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.
Time frame: Week 13
Plan to share: No
No publications or documents are linked to this record.
Started Nov 2025 (actual). Primary completion is estimated for Oct 2027, 23 months after the start.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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