NCT07503444 · UCB BIOSCIENCES, Inc.
A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome
What this study is about
The purpose of this study is to investigate the effectiveness of fenfluramine hydrochloride (HCl) versus placebo in study participants with Rett syndrome (RTT).
View original scientific description
The purpose of this study is to investigate the efficacy of fenfluramine hydrochloride (HCl) versus placebo in study participants with Rett syndrome (RTT).
Interventions
DRUG
fenfluramine hydrochloride
Oral solution
OTHER
Placebo
Oral solution
Primary outcome measures
Change from Baseline to Week 14 in Rett Syndrome Behaviour Questionnaire (RSBQ) Total Score
Time frame: From Baseline (Day 1) to Week 14
The RSBQ is a caregiver-completed, instrument assessing behavioral and emotional features in RTT. The RSBQ consists of 45 items, including 8 subscales: General mood (8 items); Breathing problems (5 items); Hand behavior (6 items); Face movements (4 items); Body rocking and expressionless face (6 items); Nighttime behaviors (3 items); Fear/anxiety (4 items); and Walking/standing (2 items). Caregivers are asked to evaluate each RTT feature based on the current status of the patients on a 3-point scale as 0 ("not true"), 1 ("somewhat or sometimes true"), or 2 ("often true"), with the total score ranging from 0 to 90. Higher scores indicate increased disease severity. Seven items that do not belong under any of the subscales are classed as "uncategorized" but contribute to the overall total score.
Clinical Global Impression of Change (CGIC) Score at Week 14
Time frame: At Week 14
The CGIC is a clinician-rated single item evaluating the degree of improvement or worsening of a participant's condition from Baseline following treatment or intervention. The CGIC uses a 7-point response scale, with the following ratings: "1: Very Much improved", "2: Much improved", "3: Minimally improved", "4: No change", "5: Minimally worse", "6: Much worse", "7: Very Much Worse".
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
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
Where
- Little Rock, Arkansas
- Orlando, Florida
- Atlanta, Georgia
- Houston, Texas
- Irving, Texas
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Aug 17, 2026 · Source of record for eligibility and locations