Snapshot A 23-year-old woman presents to the clinic for her annual well exam. She is relatively healthy and denies any pressing concerns. Her medical history is unremarkable. A routine laboratory test demonstrates high levels of serum calcium. Further urine testing shows low levels of urine calcium. Introduction Clinical definition rare disorder characterized by inactivating mutations in the gene for calcium-sensing receptors (CaSR) leading to mild hypercalcemia and hypocalciuria normal to increased parathyroid hormone (PTH) levels ETIOLOGY Pathogenesis autosomal dominant loss of function mutations of the CaSR gene, which is expressed in multiple tissues (e.g., parathyroid glands, kidneys, bone marrow, breast, intestines, and some areas of the brain) results in reduced receptor stimulation higher levels of normal calcium levels are required to suppress PTH, resulting in a new equilibrium level at the kidney, the defect results in an increase of tubular calcium and magnesium reabsorption Presentation Symptoms often asymptomatic signs of hypercalcemia (uncommon) constipation polyuria renal insufficiency neuropsychiatric signs Physical exam no significant physical examination findings Studies Diagnostic testing diagnostic approach characteristic laboratory findings (e.g., hypercalcemia and hypocalciuria) and clinical history (e.g., asymptomatic or positive family history) establishes the diagnosis studies serum calcium level often high normal or slightly elevated serum PTH level abnormally normal or elevated 24-hour urine calcium low levels (calcium excretion rate < 0.02 mmol/L) genetic testing not required for diagnosis Differential Primary hyperparathyroidism differentiating factor familial hypocalciuric hypercalcemia (FHH) usually presents with hypocalciuria while primary hyperparathrydoidism will present with hypercalciuria no significant symptoms in patients with FHH Treatment Management approach as FHH is a benign condition of hypercalcemia, no treatment is generally required affected family members should be identified and counseled on the nature of the condition it is important to avoid parathyroidectomy or any other aggressive intervention as they would not cure the disorder Complications Due to the benign nature of the disease, no significant complications are associated with FHH