Efficacy and Safety of Encaleret Compared to Standard of Care in Participants With ADH1

Key Inclusion Criteria:

1. Participants must have a documented pathogenic or likely pathogenic activatingvariant, or variant of uncertain significance, of the calcium sensing receptor (CASR) gene associated with biochemical findings of hypoparathyroidism.

2. Participants must have a documented history of symptoms or signs of ADH1.

3. Participants 16 to <18 years old must have closed growth plates on hand radiograph.

4. Participants treated with thiazide diuretics must discontinue thiazides for at least 14 days prior to SoC Optimization Visit 1 through Week 24 (Period 3). When thethiazide is being used as an antihypertensive, alternative therapy will beprescribed by the Investigator as needed.

5. Participants treated with phosphate binders (other than calcium salts) mustdiscontinue the phosphate binders at least one day prior to the SoC OptimizationVisit 1.

6. Participants treated with magnesium or potassium supplements must be willing todiscontinue such treatment prior to the first dose of encaleret.

7. Participants treated with potassium-sparing diuretics must be willing to discontinuesuch treatment prior to the first dose of encaleret.

8. Participants must meet SoC Optimization criteria as defined in the protocol.

Key Exclusion Criteria:

1. History of hypocalcemic seizure within the past 3 months preceding Screening.

2. History of thyroid or parathyroid surgery.

3. History of renal transplantation.

4. Pregnant or nursing (lactating) women, where pregnancy is confirmed by a positivebeta-human chorionic gonadotropin (β-hCG) laboratory test.

5. History of treatment with parathyroid hormone (PTH) 1-84 or 1-34 within the 2 monthspreceding Screening and requiring SoC doses exceeding >1.2× their pre-PTH treatmenttotal daily doses or bone turnover markers, Collagen cross-linked C-telopeptide (CTx )and Procollagen type 1 N-propeptide (P1NP), > upper limit of normal for sex, age (men only) and menopausal status (women only).

6. Blood 25-OH Vitamin D level <25 nanograms (ng)/milliliter (mL).

7. Estimated glomerular filtration rate (eGFR) <30 mL/minute/1.73 m^2 using chronickidney disease-EPI creatinine equation refit without the race variable (chronickidney disease-EPI creatinine equation refit without the race variable [CKD-EPIcr_R]) (for participants <18 years old the Bedside Schwartz equation shouldbe used).

8. Participants with positive Hepatitis B surface antigen (HBsAg), Hepatitis Aimmunoglobulin M (IgM), or human immunodeficiency virus (HIV) viral serology test atthe Screening Visit. Participants who are in complete remission from Hepatitis Cvirus (HCV) as evidenced by sensitive assay ≥12 weeks after completion of HCVtherapy may participate in the study.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.