A Phase 3 interventional study of NNZ-2591 in Phelan-McDermid Syndrome, sponsored by Neuren Pharmaceuticals Limited. Recruiting at 12 sites in United States. Open to participants aged 3 Years to 12 Years. Per ClinicalTrials.gov, last updated 2026-11-09.
Sponsored by Neuren Pharmaceuticals Limited · Phase 3, Interventional, and Treatment
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.
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.
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 up to 56 weeks.
Drug: NNZ-2591
The study drug will be administered twice daily orally.
Long-term safety and tolerability of NNZ-2591 as assessed by the incidence of adverse events across participants
Incidence of TEAEs, AESI and SAEs across participants
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline in ECG Heart Rate (bpm)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline PR Interval (ms QRS interval (ms)
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline in QT interval (ms)
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline in QTcB interval (ms)
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline in QTcF interval (ms)
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of ECG parameters events across participants.
Change from Baseline in RR interval (ms)
Time frame: Baseline through Safety Follow-Up (Month 12)
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.
Change from Baseline for heart rate (bpm)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.
Change from Baseline for respiration rate (breaths per minute)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.
Change from Baseline for Temperature (Celsius)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.
Change from Baseline for Diastolic Blood Pressure (mm Hg)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as assessed by changes from Baseline assessments of vital sign parameters events across participants.
Change from Baseline for Systolic Blood Pressure (mm Hg)
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as incidence of abnormal, clinically significant clinical laboratory parameters events across participants.
Incidence of abnormal and clinically significant laboratory parameters
Time frame: Baseline through Month 12
Long-term safety and tolerability of NNZ-2591 as incidence of abnormal, clinically significant physical examination findings across participants.
Incidence of abnormal, clinically significant physical examination findings
Time frame: Baseline through Month 12
Efficacy of NNZ-2591 as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) overall score
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.
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.
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.
Time frame: Months 3 and 12
Efficacy of NNZ-2591 as measured by the Phelan-McDermid Syndrome Assessment of Change (PMSA-C) domain scores.
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.
Time frame: Months 3 and 12
Efficacy of NNZ-2591 as measured by the Caregiver Impression of Change (CIC) domain scores.
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.
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.
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.
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.
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.
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.
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.
Time frame: Months 3 and 12
Plan to share: No
No publications or documents are linked to this record.
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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Neuren Pharmaceuticals Limited