Multicenter,Single-arm Study to Evaluate Efficacy, Safety, & Pharmacokinetics of Denosumab in Children w/ OI

• Eligibility criteria relates to initial enrollment into this study (6-Month Dosing Regimen). Subjects reconsenting to a 3-Month Dosing Regimen will not repeat eligibility assessments Inclusion Criteria: • Clinical diagnosis of OI defined as a clinical history consistent with type I-IV OI Clinical severity of OI as defined by 2 or more prevalent vertebral compression fractures; OR1 prevalent vertebral compression fracture and 1 or more nonvertebral fractures within the previous 2 years; OR 3 or more fractures within the previous 2 years. Exclusion Criteria: • Inability or unwillingness to comply with the requirements for frequent calcium and phosphorus monitoring for 14 days after the first dose of denosumab (only applies to the first 5 subjects age 11 to17 enrolled in the study and the first 5 subjects of any age meeting the criteria for increased bone turnover • Currently unhealed fracture or osteotomy as defined by orthopedic opinion • Osteotomy within 5 months of screening • Evidence of untreated oral cavities or oral infections • Recent or planned invasive dental procedure • Surgical tooth extraction which has not healed by screening • History of an electrophoresis pattern inconsistent with type I to IV OI • History of genetic testing results inconsistent with type I to IV OI • Abnormalities of the following per central laboratory reference ranges at screening: Serum albumin corrected calcium < lower limit of normal (LLN) Serum vitamin D < 20 ng/mL; re-screening for Vitamin D level < 20 ng/mL will be allowed, after adequate supplementation • Aspartate aminotransferase (AST), alanine aminotransferase (ALT) > 1.5 x upper limit of normal (ULN) • Total bilirubin (TBL) > 1.5 x ULN (subjects with Gilbert syndrome are eligible) • Serum phosphorus < LLN • Serum alkaline phosphatase > 20% above the ULN or > 20% below the LLN • Estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 (calculated bythe Schwartz equation at screening) Evidence of any of the following: Current hyperthyroidism (unless well-controlled on stable antithyroid therapy) • Current clinical hypothyroidism (unless well-controlled on stable thyroid replacement therapy) • History of hyperparathyroidism • Current hypoparathyroidism • Current, uncontrolled hypercalcemia (albumin-corrected serum Ca >10% ULN) • History of osteomalacia or rickets (chart review) • Other bone diseases that affect bone metabolism (eg, osteoporosis pseudoglioma syndrome, idiopathic juvenile osteoporosis, osteopetrosis, hypophosphatasia) • History of autoimmune disease • History of rare hereditary problems of fructose intolerance • Positive blood screen for human immunodeficiency virus -1 or -2 antibody • Positive blood screen for hepatitis B surface antigen or hepatitis C antibody • Received other osteoporosis treatment or bone active treatment with the following guidelines: • Prior treatment with - denosumab - fluoride or strontium for bone disease (fluoride taken for routine dental care is permitted) - parathyroid hormone (PTH) or PTH derivatives within 12 months prior to screening - zoledronic acid within 6 months prior to screening - oral bisphosphonates or intravenous bisphosphonates other than zoledronic acid if the first dose of denosumab would be before their next scheduled bisphosphonate dose would have been given • Administration of systemic glucocorticoids (≥ 5.0 mg prednisone equivalents/day for more than 10 days) within 3 months of screening. • Topical and inhaled glucocorticoids will be allowed • Administration of any of the following treatment within 3 months of screening: - Growth hormone (subjects on stable dose of growth hormone for at least 3 months prior to screening will be allowed) • Currently receiving treatment in another investigational drug study, or less than 30 days since ending treatment on another investigational drugstudy(s), or current or planned participation in a clinical trial that would preclude compliance with study requirements Other inclusion/exclusion criteria may apply.