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Updated: Dec 9 2021

Familial Hypocalciuric Hypercalcemia

  • 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
    • 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
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