<h4>Context</h4>Although a monoallelic mutation in the calcium-sensing receptor (<i>CASR</i>) gene causes familial hypocalciuric hypercalcemia (FHH), the functional characterization of the identified <i>CASR</i> mutation linked to the clinical response to calcimimetics therapy is still limited.<h4>Objective</h4>A 45-year-old male presenting with moderate hypercalcemia, hypocalciuria, and inappropriately high parathyroid hormone (PTH) had a good response to cinacalcet (total serum calcium (Ca<sup>2+</sup>) from 12.5 to 10.1 mg/dl). The gene discussed is PTH; the disease is familial hypocalciuric hypercalcemia.