Updated: 4/29/2019

Familial Hypocalciuric Hypercalcemia

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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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