Background and Objectives:Phelan-McDermid syndrome (PMS) is a rare genetic neurodevelopmental disorder with no currently approved treatments. NNZ-2591, a synthetic analog of the insulin-like growth factor 1 metabolite cyclic glycine-proline, was evaluated in children and adolescents with PMS in a phase 2, multisite, open-label clinical trial.
Methods:Participants aged 3-12 years at screening received twice-daily oral NNZ-2591 for 13 weeks; doses were uptitrated from 4 mg/kg to 12 mg/kg over 6 weeks (NCT05025241). Safety and pharmacokinetic profiles were primary end points; 14 efficacy assessments were secondary end points, which included global and symptom-specific PMS assessments, quality of life, communication, behavior, adaptive behavior/self-care, gastrointestinal health, and sleep assessments. Wilcoxon signed-rank tests evaluated change from or observed change relative to baseline vs the null median, with p < 0.05 indicating significance.
Results:Eighteen participants received NNZ-2591 (mean [SD] age 8.6 years, mean [SD] weight: 30.4 [10.8] kg). NNZ-2591 was well tolerated; most treatment-emergent adverse events were mild to moderate. Significant improvements from baseline were observed in 10 of 14 efficacy assessments at week 13, including global and symptom-specific PMS assessments, quality of life, behavior, gastrointestinal symptoms, and sleep. At week 13, the PMS-specific Clinical Global Impression (CGI) of Improvement mean (SD) score was 2.4 (0.9) and the median (range) score was 2.0 (1.0, 4.0) (p < 0.0001), with 16 of 18 participants showing improvement; the PMS-specific Caregiver Impression of Change mean (SD) score was 2.7 (1.0) and the median (range) score was 3.0 (1.0, 5.0) (p = 0.0003), with 15 of 18 participants showing improvement. PMS-specific assessment subdomains of communication, cognition/learning, and socialization showed consistent improvements. A 24-hour steady-state area under the curve (AUC24,ss) was estimated for each participant using a one-compartment, linear, population pharmacokinetic model where clearance and volume of distribution parameters were scaled by body weight. Participants with an NNZ-2591 AUC24,ss > 300 μg ⋅ h/mL experienced improvements in the PMS-specific CGI of Improvement scores.
Discussion:For children and adolescents with PMS, NNZ-2591 appeared generally safe, with clinicians and caregivers reporting meaningful improvements in important symptoms of PMS. The benefit-risk and pharmacokinetic profiles support continued evaluation of NNZ-2591 for PMS.
Trial Registration Information:ClinicalTrials.gov; NCT05025241. Submitted August 24, 2021. First participant enrolled on August 8, 2022.