Open Label Trial Assessing Safety and Efficacy of Burosumab (KRN23), in a Patient With ENS and Hypophosphatemic Rickets

1.1 Primary Objective The effect of KRN23 treatment on normalizing age-adjusted serum phosphorous levels in a single pediatric patient with Epidermal Nevus Syndrome associated hypophosphatemic rickets 1.2 Secondary Objectives 1. The PD profile of KRN23 as assessed by changes from baseline over time 1,25(OH)2D, iPTH, Serum Calcium, TRP and TmP/GFR (the ratio of renal tubular maximum phosphate reabsorption rate to glomerular filtration rate) 2. Changes in underlying skeletal disease/rickets as assessed by standard radiographs utilizing the Radiographic Global Impression of Change (RGI-C) rating scales 3. Effects of KRN23 on biochemical markers of bone turnover that reflect rickets severity, alkaline phosphatase (ALP) 4. Walking ability as assessed by 6-Minute Walk Test (6MWT) 5. Patient/parent-Reported Outcomes as assessed by PROMIS and FPS-R rating scales 1.3 Exploratory Objective 1\. Dual-energy X-ray absorptiometry (DXA) 1.4 Safety Objective Assess the safety of KRN23 administration in a single patient with ENS-associated hypophosphatemic rickets, based on adverse events (AEs), laboratory assessments, cardiac imaging and renal ultrasound.