Familial Hypocalciuric Hypercalcemia

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Presentation :

• Most common type of familial hypercalcemia
• Family history of parathyroidectomy without resolution of hypercalcemia

Pathophysiology :

• Autosomal dominant inactivating mutation of the calcium-sensing receptor (CaSR) which causes the parathyroid gland to perceive serum calcium concentrations as low resulting in increased PTH secretion and a higher serum calcium level
• The mutated CaSR in the kidney also increases kidney resorption of calcium, leading to paradoxical hypocalciuria in the setting of hypercalcemia

Diagnostic Testing:

• Hypercalcemia and hypocalciuria (low 24h urine Ca)
  • Especially helpful if calcium-creatinine clearance ratio is less than 0.0
• Inappropriately normal or elevated PTH level
• If clinically ambiguous, can be confirmed by CaSR genetic testing

Treatment :

• Parathyroidectomy is not indicated because hypercalcemia will not resolve with surgery.

Prognosis:

• FHH is a benign condition because patients do not have sequelae of hypercalcemia.

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