This trial will enroll adolescents between ages of ≥12 and <18 years with clinically diagnosed hypoparathyroidism . The purpose of the study is to see how well treatment with once-daily palopegteriparatide works and how safe it is. At least 12 participants will receive palopegteriparatide for 234 weeks. This trial will be conducted in Europe.

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