This study is to evaluate the safety and efficacy of AGA2115 at three different dose regimens in Chinese adults and adolescents with Type I, III, or IV Osteogenesis imperfecta (OI).

This Phase 2 study will evaluate the safety and efficacy of AGA2115 in three different dosing regimens in Chinese adults and adolescents with Type I, III, or IV OI. Participants will be in the study for 24 or 27 months depending on their assigned cohort. During the first 12 months of the study, adult and adolescent participants will be randomized separately in a 1:1:1:1 ratio to one of three AGA2115 dosing regimens or control cohort. During months 12 to 24 or 27, all participants will receive AGA2115 and attend visits for the evaluation of safety and efficacy parameters.

Inclusion Criteria:

• Adults (18-75 years) or adolescents (12-17 years) with a confirmed diagnosis of Osteogenesis Imperfecta (OI) Type I, III, or IV with genetic confirmation of pathogenic variants in COL1A1 or COL1A2 genes
• BMD T-score of ≤-1.0 at the lumbar spine, total hip, or femoral neck (adults) or BMD Z-score of ≤-1.0 at the lumbar spine, total hip, or femoral neck (adolescents)
• Capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol

Exclusion Criteria:

• Vitamin D deficiency
• Concomitant uncontrolled diseases or conditions that could affect bone metabolism such as hypo-/hyperparathyroidism, hypo-/hyperthyroidism, abnormal thyroid function or thyroid disease, or other endocrine disorders.
• Current hyper- or hypocalcemia.
• History of rickets, osteomalacia, or other significant skeletal disorders (excluding OI) leading to long-bone deformities and/or increased risk of fractures.
• Use of bisphosphonates within the past 6 months.
• Use of teriparatide, abaloparatide, strontium ranelate, or hormone replacement therapy within the past 12 months.
• Use of denosumab (or denosumab biosimilars) within the past 2 years.
• Use of anti-sclerostin antibody medications (romosozumab, setrusumab, blosozumab) at any time.
• History of myocardial infarction or stroke (or other cardiovascular associated event deemed significant) within the past 12 months.
• Malignancy within the last 5 years.
• Pregnant or breastfeeding women, or women planning to become pregnant during the study or within 4 months after the last dose of IP.