Open-label Extension of Study 20130173 of Denosumab in Children and Young Adults With Osteogenesis Imperfecta

Inclusion Criteria: * Subject has provided informed consent/assent prior to initiation of any Study 20170534 specific activities/procedures. Subject's legally acceptable representative has provided informed consent when the subject is legally too young to provide informed consent and the subject has provided written assent based on local regulations and/or guidelines prior to any study-specific activities/procedures being initiated. * Subject is currently/was enrolled in Study 20130173 and * completed the 20130173 End of Study (EOS) visit (regardless of completing or ending investigational product early) OR * did not reconsent/reassent to transition to 3-month dosing regimen on Study 20130173 OR * early terminated from Study 20130173 as a result of meeting bone mineral density (BMD) Z-score investigational product stopping criteria. Exclusion Criteria: * Treatment with any prohibited proscribed medications while receiving denosumab. Eligibility into study treatment with alternative osteoporosis medication/s of investigator's choice, follow guidelines per the specific alternative osteoporosis medication/s selected. For subjects off-treatment (observation only), no prohibited medications apply. * Subjects currently receiving treatment in another investigational device or drug study other than Study 20130173. Other investigational procedures while participating in this study are excluded. * For subjects expected to receive investigational product (denosumab) at study d…