Who may be eligible for the A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome trial?

Inclusion Criteria: * Participant has typical or classic Rett Syndrome (RTT) according to the RettSearch Consortium 2010 revised criteria * Participant has a documented disease-causing mutation or deletion in the methyl-CpG-binding protein 2 (MECP2) gene * Participant meets criteria for postregression for at least 6 months prior to Screening, defined as: * No loss or degradation of ambulation (including gait, coordination, or independence of walking/standing); * No loss or degradation of hand function; no loss or degradation of speech (including babbling, words, or previously developed communicative vocalizations); * No loss or degradation of nonverbal communicative or social skills (including eye gaze, using body to indicate communicative intent, or social attentiveness) * Participant has an Rett Syndrome Clinical Severity Scale (RTT-CSS) rating of 10 to 36 (inclusive) * Participant has a Clinical Global Impression-Severity (CGIS) score of ≥4 * Participant has a legal representative capable of providing signed informed consent on behalf of the participant as described in the protocol, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol. * Participant is aged 5 to 35 years of age (inclusive) at the time of first administration of investigational intervention. * Male or female. * Participant has a consistent caregiver who is ≥18 years of age at the Screening Visit. The caregiver needs to be able to complete the caregiver assessments defined for the entire study. Every attempt should be made to have the same evaluator complete the assessments for the duration of the study. Exclusion Criteria: * Participant has a history of lymphoma, leukemia, or any malignancy within the past 5 years except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 3 years. * Participant has clinically significant abnormality in vital signs according to the Investigator * Participant has an exclusionary cardiovascular or cardiopulmonary abnormality based on echocardiogram (ECHO), electrocardiogram (ECG), or physical examination, and is not approved for entry by the central cardiac reader. Exclusionary abnormalities include, but are not limited to: 1. Greater than trace aortic valve regurgitation. 2. Greater than mild mitral valve regurgitation. 3. Possible signs of pulmonary arterial hypertension (PAH) with abnormal pulmonary artery systolic pressure (PASP) or PASP ≥35 mmHg. 4. Evidence of left ventricular dysfunction (systolic or diastolic). 5. Clinically significant structural cardiac abnormality, including but not limited to mitral valve prolapse, atrial or ventricular septal defects, or patent ductus arteriosus with reversal of shunt (right to left shunt). Note: Patent foramen ovale without a reversal of shunt or a bicuspid aortic valve is not considered exclusionary * Participant has a clinically significant medical condition, including chronic obstructive pulmonary disease, interstitial lung disease, portal hypertension, or need for invasive mechanical ventilation (eg, via tracheostomy), or has had clinically relevant symptoms or a clinically significant illness currently or in the 4 weeks prior to the Screening Visit that would negatively impact study participation, collection of study data, or pose a risk to the participant * Participant is taking \>4 concomitant antiseizure medications (ASMs). Rescue medications are not included in the count

ClinicalTrials.gov record NCT07503444

A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome

Record copied from ClinicalTrials.gov: Oct 10, 2026AI summaries generated: Aug 22, 2026

A Phase 3 Randomized, Double-Blind, Placebo Controlled, Parallel Group, Multicenter Study With Open-Label Extension to Evaluate the Efficacy And Safety of Fenfluramine Hydrochloride in Study Participants With Rett Syndrome

About this page. This page shows the study's official ClinicalTrials.gov record ↗, with added help to make it easier to understand. We explain medical terms, highlight key details in plain language, and suggest questions you may want to ask the study team.

The record is periodically copied from ClinicalTrials.gov and may lag behind changes. AI summaries are checked by software, not a clinician.Read moreShow less

The official record is written by the study sponsor and published on ClinicalTrials.gov. It may not always reflect the latest changes. Before making any decisions, please confirm important information with the study team and your own healthcare team.

Where you see "AI summary", AI was used to create a plain-language explanation and software checked it against the source. It has not been reviewed by a clinician, so it may contain mistakes or leave out important details.

StatusRecruitingThe study is currently enrolling participants. Only the study team can say whether a particular person can join.

Study typeInterventionalA study in which researchers assign participants to one or more interventions, such as a drug, procedure, device, behavioural programme or other approach, to measure their effects.

PhasePhase 3A later-stage study, usually with more participants, designed to give stronger evidence about how well a treatment works and how safe it is. It often compares the treatment with standard care or a placebo, and results may support an application for approval.

Age5 years old to 35 years old

SexAll

LocationBelgium, France, Germany, Hungary, Italy, Japan, Poland, Spain, United States

AI summaryWhat this study is about, in plain languageShow ▾Hide ▴

AI-written from the registry record, not the study's own wording. May contain errors or omissions. Check the registry text on this page and the original record ↗ before acting on it.

This Phase 3 randomized, triple-masked study compares fenfluramine hydrochloride with placebo in people with Rett Syndrome. The study includes a 14-week double-blind period (titration and maintenance), a 2-week double-blind transition, then a 52-week open-label treatment period; participants who stop without continued access follow an 8-day taper and a 26-week follow-up. Outcomes include a caregiver-rated behavior questionnaire (RSBQ), clinician global impression, sleep and communication measures, seizure change, and extensive safety monitoring including ECG and echocardiogram results.

What it is studying. Whether fenfluramine hydrochloride produces different effects than placebo on behavior and overall clinical change in people with Rett Syndrome, and to assess safety measures such as adverse events, ECG (QTcF), and echocardiogram findings.

What the researchers hope to learn. Primary scientific goals are to measure change from baseline to Week 14 in the Rett Syndrome Behaviour Questionnaire (RSBQ) total score and the clinician-rated Clinical Global Impression of Change (CGIC) at Week 14. Secondary goals include measuring sleep disturbance, communication ability, caregiver-rated seizure change, and safety outcomes (treatment-emergent adverse events, serious adverse events, ECG QTcF changes, and echocardiogram findings) up to the end of safety follow-up.

What this study is about

The study's own summary, as published on ClinicalTrials.gov. Underlined terms have a short explanation.

The purpose of this study is to investigate the efficacy of fenfluramine hydrochloride (HCl) versus placebo in study participants with Rett syndrome (RTT).

Interventions being studied

Being studied in this trial does not mean the treatment or procedure is approved or available for this condition.

Drug: fenfluramine hydrochloride
Other: Placebo

Eligibility

The criteria exactly as listed on ClinicalTrials.gov. Only the study team can say whether they apply to you.

Inclusion criteria

Participant has typical or classic Rett Syndrome (RTT) according to the RettSearch Consortium 2010 revised criteria
Participant has a documented disease-causing mutation or deletion in the methyl-CpG-binding protein 2 (MECP2) gene
Participant meets criteria for postregression for at least 6 months prior to Screening, defined as:
No loss or degradation of ambulation (including gait, coordination, or independence of walking/standing);
No loss or degradation of hand function; no loss or degradation of speech (including babbling, words, or previously developed communicative vocalizations);
No loss or degradation of nonverbal communicative or social skills (including eye gaze, using body to indicate communicative intent, or social attentiveness)
Participant has an Rett Syndrome Clinical Severity Scale (RTT-CSS) rating of 10 to 36 (inclusive)
Participant has a Clinical Global Impression-Severity (CGIS) score of ≥4
Participant has a legal representative capable of providing signed informed consent on behalf of the participant as described in the protocol, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol.
Participant is aged 5 to 35 years of age (inclusive) at the time of first administration of investigational intervention.
Male or female.
Participant has a consistent caregiver who is ≥18 years of age at the Screening Visit. The caregiver needs to be able to complete the caregiver assessments defined for the entire study. Every attempt should be made to have the same evaluator complete the assessments for the duration of the study.

Exclusion criteria

Participant has a history of lymphoma, leukemia, or any malignancy within the past 5 years except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 3 years.
Participant has clinically significant abnormality in vital signs according to the Investigator
Participant has an exclusionary cardiovascular or cardiopulmonary abnormality based on echocardiogram (ECHO), electrocardiogram (ECG), or physical examination, and is not approved for entry by the central cardiac reader. Exclusionary abnormalities include, but are not limited to:
Greater than trace aortic valve regurgitation.
Greater than mild mitral valve regurgitation.
Possible signs of pulmonary arterial hypertension (PAH) with abnormal pulmonary artery systolic pressure (PASP) or PASP ≥35 mmHg.
Evidence of left ventricular dysfunction (systolic or diastolic).
Clinically significant structural cardiac abnormality, including but not limited to mitral valve prolapse, atrial or ventricular septal defects, or patent ductus arteriosus with reversal of shunt (right to left shunt). Note: Patent foramen ovale without a reversal of shunt or a bicuspid aortic valve is not considered exclusionary
Participant has a clinically significant medical condition, including chronic obstructive pulmonary disease, interstitial lung disease, portal hypertension, or need for invasive mechanical ventilation (eg, via tracheostomy), or has had clinically relevant symptoms or a clinically significant illness currently or in the 4 weeks prior to the Screening Visit that would negatively impact study participation, collection of study data, or pose a risk to the participant
Participant is taking >4 concomitant antiseizure medications (ASMs). Rescue medications are not included in the count

Study description and what participation involves

The registry record has no detailed description beyond the summary above.

AI summaryWhat participation may involve, in plain languageShow ▾Hide ▴

AI-written from the registry record, not the study's own wording. May contain errors or omissions. Check the registry text on this page and the original record ↗ before acting on it.

Participants are randomly assigned to take an oral fenfluramine hydrochloride solution or a matching placebo during a 14-week double-blind period that includes dose titration and maintenance. After a 2-week double-blind transition, all participants enter a 52-week open-label treatment period; some may continue treatment until alternative access is available. Study visits include caregiver-completed questionnaires about behavior, sleep, communication and seizures, clinician ratings, and heart tests (12-lead ECG and Doppler echocardiogram) with ongoing safety monitoring for adverse events. Participants who stop treatment without continued access will undergo an 8-day taper and a 26-week follow-up; safety follow-up is reported for up to 3 years and 10 months.

How the study is structured. Randomized, triple-masked (participants and study staff masked), parallel-group trial. Participants are assigned to fenfluramine hydrochloride or matching placebo for a 14-week double-blind period (with titration and maintenance), followed by a 2-week double-blind transition and a 52-week open-label treatment period. Those who discontinue without continued access undergo an 8-day taper and are followed for 26 weeks; safety follow-up extends up to 3 years and 10 months.

Questions you could ask

These questions are suggestions for a conversation with the study team or your own clinician, not advice.

Some participants receive a placebo. How is that decided, and what happens for placebo-group participants when the study ends?
The listed sites are in Belgium, France, Germany, Hungary, Italy, Japan, Poland, Spain, United States. Is any of them reachable for me, and does the study help with travel?
Which of the eligibility criteria would need to be checked with tests before I could join?

More on Rett syndrome

Clinical trials20 trials listed for Rett syndromeEvery trial the registry lists for Rett syndrome, with recruitment status, phase and sites, updated from ClinicalTrials.gov.See all trials →Research updatesWhat changed in Rett syndrome researchLatest monthly update: September 2026. Includes: Seizure add-on drug. New research summarized each month in plain language, with links to every source paper.Read the latest update →

Important dates

Study start: Jul 14, 2026
Primary completion: Feb 6, 2029 (estimated)
Study completion: Aug 29, 2031 (estimated)
Target enrollment: 200 participants (estimated)
Last updated on registry: Oct 2, 2026
Data verified: Oct 10, 2026

Sponsor and research team

The lead sponsor funds and oversees the trial. A pharmaceutical or biotech company sponsor typically means the study is testing that company's drug or device; a hospital, university, or government agency usually indicates investigator-initiated or publicly funded research.

Lead sponsor: UCB BIOSCIENCES, Inc.

Central study contact

If you're interested in participating, the central contact can answer general questions about the study — including eligibility requirements and how to find a recruiting site near you. Actual eligibility is determined by the site's medical team.

UCB Cares 📞 +18445992273 ✉ ucbcares@ucb.com
UCB Cares 📞 0018445992273 ✉ UCBCares@ucb.com

Participating sites (32)

Filter by country:

Ep0247 21010Recruiting
Little Rock, Arkansas, 72202 · United States
Ep0247 21009Recruiting
Miami, Florida, 33155 · United States
Ep0247 21011Recruiting
Orlando, Florida, 32806 · United States
Ep0247 21007Recruiting
Atlanta, Georgia, 30322 · United States
Ep0247 21003Recruiting
Philadelphia, Pennsylvania, 19104-4318 · United States
Ep0247 21005Recruiting
Houston, Texas, 77030 · United States
Ep0247 21013Recruiting
Irving, Texas, 75062 · United States
Ep0247 21004Recruiting
Seattle, Washington, 98105 · United States
Ep0247 11001Recruiting
Brussels · Belgium
Ep0247 12005Recruiting
Brest · France

Terms used on this page · explanations by MedicalUpdates.ai

placebo: A treatment that looks like the study treatment but contains no active ingredient. Some participants receive it instead of the study treatment, usually without knowing which they got.
prior to Screening: The checks done before enrolment to see whether a person qualifies, such as tests, scans or a review of medical history.
legal representative: A person who is legally allowed to make decisions, including consent to research, on behalf of someone who cannot consent for themselves.
informed consent: The process of explaining a study, including its risks and what participation involves, so that a person can decide freely whether to take part. Consent is usually documented in writing, and a participant can choose to leave the study later.
investigational: A treatment that is being tested and has not been approved for this use. It may be approved for a different condition. Being studied does not mean it works or is available outside the study.
echocardiogram: An ultrasound scan of the heart. A transesophageal echocardiogram is done through a probe passed into the food pipe for a closer view.
electrocardiogram: A recording of the heart's electrical activity. QTc is one measurement from it; some drugs are avoided if it is prolonged.
Inclusion Criteria: The conditions a person must meet to be considered for the study, for example a confirmed diagnosis, an age range or a test result.
Exclusion Criteria: The conditions that rule a person out even if they meet the inclusion criteria, for example other illnesses, certain medicines or pregnancy.

The study record on this page is reproduced from ClinicalTrials.gov, a database of the U.S. National Library of Medicine, where it was submitted by the study sponsor. MedicalUpdates.ai does not own this content, is not affiliated with or endorsed by ClinicalTrials.gov, NIH, or the U.S. Government, and does not verify the record. Plain-language notes, the glossary and the questions above are added by this site; text in the boxes marked "AI summary" was written by an AI model and may contain errors. Registry records change over time. Check the original record for the current version and discuss eligibility or participation with a qualified healthcare professional.

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