A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome

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.

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".

Sleep disturbances will be assessed by the PROMIS-SD parent proxy 8a version. Caregivers are asked to rate 8 items over the past 7 days on a 5-point scale: "1: Never", "2: Almost never", "3: Sometimes", "4: Almost always", and "5: Always", with higher scores indicating more severe sleep disturbances.

The ORCA is an 84-item, observer-reported measure of communication ability over the past 30 days. The majority of the items included in the ORCA measure have 3 response options: "No or only once," "Sometimes," and "Yes, almost all the time", which enable derivation of an overall communication score and scores for each form of communication (expressive, receptive, and pragmatic), with higher scores indicating greater communication ability.

The CaGIC-Seizure is a caregiver-reported item assessing the change from Baseline in the participant's seizure status. The CaGIC-Seizure 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".

An AE is any untoward medical occurrence in a clinical study participant temporally associated with the use of study intervention, whether or not considered related to the study intervention. Treatment emergent adverse events (TEAEs) are adverse events that are not present prior to the pharmaceutical product administration or an already present event that worsens either in intensity or frequency.

An SAE is defined as any untoward medical occurrence that, at any dose, meets 1 or more of the criteria listed:

• Results in death
• Is life-threatening
• Requires inpatient hospitalization or prolongation of existing hospitalization
• Results in persistent or significant disability/incapacity
• Is a congenital anomaly/birth defect
• Other important medical events which based on medical or scientific judgement may jeopardize the patients or may require medical or surgical intervention to prevent any of the above.

An AE is any untoward medical occurrence in a clinical study participant temporally associated with the use of study intervention, whether or not considered related to the study intervention. Treatment emergent adverse events (TEAEs) are adverse events that are not present prior to the pharmaceutical product administration or an already present event that worsens either in intensity or frequency. TEAEs leading to discontinuation will be reported.

An AE is any untoward medical occurrence in a clinical study participant temporally associated with the use of study intervention, whether or not considered related to the study intervention. Treatment emergent adverse events (TEAEs) are adverse events that are not present prior to the pharmaceutical product administration or an already present event that worsens either in intensity or frequency. Related TEAEs will be reported.

Change from Baseline in QTcF interval as measured by 12-lead ECG at Week 14 will be reported.

The FDA case definition of drug-associated VHD is aortic regurgitation ≥mild and/or mitral regurgitation ≥moderate with restricted valve motion, valve thickening, and/or physical signs or symptoms attributable to valve diseases. ECHO readings related to VHD on any of the 4 valves (aortic, mitral, pulmonary, tricuspid) will be reported with grades of absent, trace, mild, moderate, or severe.

ECHO readings related to pulmonary arterial hypertension (PAH) on any of the 4 valves (aortic, mitral, pulmonary, tricuspid) will be reported with grades of absent, trace, mild, moderate, or severe.