Hypercalcemia, Familial Hypocalciuric

• • Benign condition of chronic, nonprogressive hypercalcemia with mildly elevated intact parathyroid hormone

  • Family history of hypercalcemia, especially in children

  • Etiology is a defect in the gene coding for the calcium sensing receptor; autosomal dominant transmission

  • Essentially is an elevation in the calcium set point

  • Often discovered incidentally with screening laboratory studies

Symptoms and Signs

• • Usually none

  • May have polyuria and polydipsia or thirst

Laboratory Findings

• • High serum calcium

  • Normal or mildly elevated intact parathyroid hormone level

  • Low urinary calcium

  • Urinary calcium clearance to creatinine clearance ratio of < 0.01

  • Possibly high serum magnesium level

Rule Out

• • Primary hyperparathyroidism

• • Complete history (including family) and physical exam

  • Direct genetic testing for calcium sensing receptor defect

• • None required

  • Operative neck exploration does not alleviate this condition (with the exception of total parathyroidectomy, and surgically induced permanent hypoparathyroidism)

  • Genetic counseling important; offspring homozygous for mutation have severe neonatal hyperparathyroidism, which is potentially lethal

References