A Study to Test the Effects and Safety of Palopegteriparatide in Adolescents With Long-term Hypoparathyroidism

Inclusion Criteria: * 1\. Males and females, 12 to less than 18 years of age * 2\. Participants with postsurgical chronic hypoparathyroidism, or auto-immune, genetic, or idiopathic hypoparathyroidism for at least 26 weeks * 3\. Normal levels of serum 25(OH) vitamin D and magnesium * 4\. Estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 * 5\. Able to perform daily subcutaneous self-injections of palopegteriparatide (or have a caregiver to perform injections) * 6\. Body mass index (BMI) Z-score greater than -2 SDS and below + 3 SDS * 7\. Written, signed informed consent Exclusion Criteria: * 1\. Impaired responsiveness to PTH which is characterized as PTH-resistance, with elevated PTH levels in the setting of hypocalcemia * 2\. Any disease that might affect calcium metabolism or calcium-phosphate homeostasis or PTH levels other than hypoparathyroidism, such as active hyperthyroidism * 3\. Use of loop diuretics, phosphate binders (other than calcium supplements), digoxin, lithium, methotrexate, biotin \>30 µg/day, or systemic corticosteroids (other than as replacement therapy). Short course use of steroids (≤2 weeks/year) equivalent to prednisone ≤60 mg/day is permitted * 4\. Use of thiazide diuretic * 5\. Use of PTH-like drugs * 6\. Use of other drugs known to influence calcium and bone metabolism, such as calcitonin, fluoride tablets (\>0.5 mg/day), strontium, or cinacalcet hydrochloride, within 12 weeks prior to Screening * 7\. Use of osteoporosis therapies known to influence calcium and bone metabolism, i.e., bisphosphonate (oral or intravenous \[IV\]), denosumab, raloxifene, or romosozumab therapies within 2 years prior to Screening * 8\. Non-hypocalcemic seizure disorder with occurrence of a seizure within 26 weeks prior to Screening * 9\. Increased risk for osteosarcoma * 10\. Female participants who are pregnant, intend to become pregnant, or are lactating * 11\. Diagnosed drug or alcohol dependence within 3 years prior to Screening