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

- 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.

- 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 day 1: Female subject is pregnant or breastfeeding or planning to become pregnant or breastfeed during treatment and for an additional 5 months after the last dose of denosumab. Females of childbearing potential (Tanner Stage greater than or equal to 2) should only be included in the study after a negative highly sensitive urine or serum pregnancy test. For 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 exclusion applies. - For subjects expected to receive investigational product (denosumab) at study day 1: Female subjects of childbearing potential unwilling to practice true sexual abstinence (refrain from heterosexual intercourse) or use 1 highly effective method of contraception during treatment and for an additional 5 months after the last dose of investigational product (denosumab). For study treatment with alternative osteoporosis medication/s of investigator’s choice, follow contraception guidelines per the specific alternative osteoporosis medication/s selected. For subjects not receiving any investigational product (observation only), no contraception required. - History or evidence of any other clinically significant disorder, condition or disease (with the exception of those outlined above) that, in the opinion of the investigator or Amgen physician, if consulted, would pose a risk to subject safety or interfere with the study evaluation, procedures or completion.