A 28-year-old woman is found to have serum calcium 11.8 mg/dL, PTH 98 pg/mL (normal 15-65), phosphate 2.1 mg/dL, and 24-hour urine calcium 82 mg/day (low). Her mother had the same findings and underwent unnecessary parathyroidectomy. The CASR gene mutation is suspected. What is the most appropriate management?

• A Parathyroidectomy (subtotal)
• B Reassurance and observation — no treatment required ✓
• C Cinacalcet (calcimimetic therapy)
• D Vitamin D supplementation

Explanation

Familial Hypocalciuric Hypercalcemia (FHH) is caused by loss-of-function mutations in the calcium-sensing receptor (CASR) gene, resulting in a higher set-point for calcium sensing. The hallmark is low urine calcium excretion (calcium-to-creatinine clearance ratio <0.01) despite hypercalcemia with mildly elevated PTH. It is a benign condition requiring no intervention; parathyroidectomy (as the mother underwent) does not cure it and is contraindicated. This must be distinguished from primary hyperparathyroidism, which it mimics biochemically.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.