O39: Infant testosterone treatment does not improve neurodevelopment at 12, 24, or 36 months for boys with 47,XXY

overall score was 2.6 (0.9) and median (range) overall score was 3.0 (1, 4), with 9 of 11 participants improving; the PTHS-specific Caregiver Impression of Change mean (SD) overall score was 3.0 (1.0) and median (range) overall score was 3.0 (2, 5), with 8 of 11 participants improving.Clinicians and/or caregivers reported the greatest magnitude of improvement in the social interaction, communication, motor skills, and cognitive ability domains.At week 13 among participants completing the study, clinicians observed a 1-point decrease in severity vs baseline on the PTHS-specific Clinical Global Impression of Severity score for 6 of 11 participants (change from baseline: mean [SD], -0.5 [0.5]; median [range], -1.0 [-1, 0]); caregivers observed a decrease in severity vs baseline on the PTHS-specific Caregiver Top 3 Concerns total score for 8 of 11 participants (change from baseline: mean [SD], -1.6 [1.5]; median [range], -1.3 [-4, 0]).Changes from baseline in non-PTHS-specific efficacy measures did not reach statistical significance.Conclusion: NNZ-2591 appeared to be safe and well tolerated in children and adolescents with PTHS.Improvements were observed by clinicians and caregivers in all PTHS-specific efficacy measures, with improvements noted by clinicians and/or caregivers in important aspects of PTHS including social interaction, communication, motor skills, and cognition.