A Phase 3 Study of Fenfluramine Hydrochloride in Rett Syndrome

Change from Baseline to Week 14 in Rett Syndrome Behaviour Questionnaire (RSBQ) Total Score

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

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".

Change from Baseline to Week 14 in Patient-Reported Outcomes Measurement Information System-Sleep Disturbance (PROMIS-SD) score

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.

Change from Baseline to Week 14 in Observer-Reported Communication Ability (ORCA) score

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.

Caregiver Global Impression of Change - Seizure (CaGIC-Seizure) score at Week 14

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".

Incidence of treatment-emergent adverse events (TEAEs) during the double-blind intervention period

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.