Improvement in body composition of Japanese participants with Prader-Willi syndrome following somatropin treatment: an open-label, multi cohort Phase 3 study.

Recombinant human growth hormone (GH; somatropin) treatment has beneficial effects on body composition in patients with Prader-Willi syndrome (PWS). However, this treatment option is limited to children in most countries and to children with short stature in countries such as the USA and Japan. The aim of this multicohort study was to evaluate the effect of somatropin on body composition and to assess its safety in Japanese pediatric and adult participants with PWS. GH-naïve pediatric participants (n = 6) received somatropin 0.245 mg/kg/week, GH-treated pediatric participants (n = 7) received somatropin 0.084 mg/kg/week, and adult participants (n = 20) received somatropin 0.042 mg/kg/week for 1 month, followed by 0.084 mg/kg/week. The study met its primary endpoint in the adult cohort because the least squares mean (95% CI) of the change from baseline to Month 12 in lean body mass (LBM) (%) was greater than the prespecified efficacy criterion of 0. LBM (%) was higher at 12 months in GH-naïve pediatric participants, while GH-treated pediatric participants showed little deterioration in LBM despite reduced GH dosage. Treatment-emergent adverse events (TEAEs) were experienced by five (83.3%), five (71.4%), and 19 (95.0%) participants in the GH-naïve pediatric cohort, GH-treated pediatric cohort, and adult cohort, respectively. Most TEAEs were mild or moderate in severity. Three participants reported four serious TEAEs, and none were treatment related. Somatropin improved body composition in adult participants, enabled maintenance of body composition in pediatric participants, and demonstrated a favorable safety and tolerability profile in all PWS cohorts. (ClinicalTrials.gov ID: NCT04697381).