Fenfluramine treatment is associated with improvement in everyday executive function in preschool-aged children (<5 years) with Dravet syndrome: A critical period for early neurodevelopment

Objective: To evaluate whether fenfluramine (FFA) is associated with improvement in everyday executive function (EF)-self-regulation-in preschool-aged children with Dravet syndrome (DS).

Methods: Children with DS received placebo or FFA in one of two phase III studies (first study: placebo, FFA 0.2 mg/kg/day, or FFA 0.7 mg/kg/day added to stiripentol-free standard-of-care regimens; second study: placebo or FFA 0.4 mg/kg/day added to stiripentol-inclusive regimens). Everyday EF was evaluated at baseline and Week 14-15 for children aged 2-4 years with parent ratings on the Behavior Rating Inventory of Executive Function®-Preschool (BRIEF®-P); raw scores were transformed to T-scores and summarized in Inhibitory Self-Control Index (ISCI), Flexibility Index (FI), Emergent Metacognition Index (EMI), and Global Executive Composite (GEC). Clinically meaningful improvement and worsening were defined using RCI ≥ 90% and RCI ≥ 80% certainty, respectively. The associations between placebo vs FFA combined (0.2, 0.4, and 0.7 mg/kg/day) or individual treatment groups and the likelihood of clinically meaningful change in BRIEF®-P indexes/composite T-scores were evaluated using Somers'd; pairwise comparisons were calculated by 2-sided Fisher's Exact tests (p ≤ 0.05) and Cramér's V.

Results: Data were analyzed for 61 evaluable children of median age 3 years (placebo, n = 22; FFA 0.2 mg/kg/day, n = 15; 0.4 mg/kg/day [with stiripentol], n = 10; 0.7 mg/kg/day, n = 14 [total FFA, n = 39]). Elevated or problematic T-scores (T ≥ 65) were reported in 55% to 86% of patients at baseline for ISCI, EMI, and GEC, and in ∼33% for FI. Seventeen of the 61 children (28%) showed reliable, clinically meaningful improvement (RCI ≥ 90% certainty) in at least one BRIEF®-P index/composite, including a majority of the children in the FFA 0.7 mg/kg/day group (9/14, 64%). Only 53% of these children (9/17) also experienced clinically meaningful reduction (≥50%) in monthly convulsive seizure frequency, including 6/14 patients in the FFA 0.7 mg/kg/day group. Overall, there were positive associations between the four individual treatment groups and the likelihood of reliable, clinically meaningful improvement in all BRIEF®-P indexes/composite (ISCI, p = 0.001; FI, p = 0.005; EMI, p = 0.040; GEC, p = 0.002). The FFA 0.7 mg/kg/day group showed a greater likelihood of reliable, clinically meaningful improvement than placebo in ISCI (50% vs 5%; p = 0.003), FI (36% vs 0%; p = 0.005), and GEC (36% vs 0%; p = 0.005). For EMI, the FFA 0.7 mg/kg/day group showed a greater likelihood of reliable, clinically meaningful improvement than the FFA 0.2 mg/kg/day group (29% vs 0%; p = 0.040), but did not meet the significance threshold compared with placebo (29% vs 5%; p = 0.064). There were no significant associations between treatment and the likelihood of reliable, clinically meaningful worsening (p > 0.05).

Significance: In this preschool-aged DS population with high baseline everyday EF impairment, FFA treatment for 14-15 weeks was associated with dose-dependent, clinically meaningful improvements in regulating behavior, emotion, cognition, and overall everyday EF. These clinically meaningful improvements in everyday EF were not entirely due to seizure frequency reduction, suggesting that FFA may have direct effects on everyday EF during the early formative years of neurodevelopment.