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The diagnosis of FHH is usually made in childhood during the evaluation of asymptomatic hypercalcemia or during screening called for because of a positive family history. The condition may also present during adulthood as hypercalcemia with a normal to slightly elevated PTH.


  1. The mutation in FHH makes the calcium-sensing receptor, found on various tissues throughout the body, less sensitive to calcium. In the parathyroid glands, this means that higher serum calcium levels are needed to suppress PTH release. The defect leads to:

    1. Secretion of PTH inappropriate to calcium levels

    2. Renal absorption of calcium inappropriate to calcium levels

  2. Most patients with FHH are asymptomatic at the time of presentation.


  1. FHH is usually easily distinguished from primary hyperparathyroidism as the former usually has mildly elevated calcium levels and a normal PTH level while the latter has an elevated PTH level.

  2. Differentiation can be difficult because patients with FHH sometimes have a mildly elevated PTH, and patients with primary hyperparathyroidism often have mild hypercalcemia and have a normal PTH 10–20% of the time.

  3. Two important distinguishing features are:

    1. Patients with FHH usually have family members with FHH. The genetic defect is inherited in an autosomal dominant manner.

    2. Urinary calcium excretion is reduced in FHH (> 99% reabsorption vs < 99% in primary hyperparathyroidism).

  4. Diagnostic Testing

    1. Patients with FHH will have hypercalcemia and a normal or slightly elevated PTH.

    2. In the setting of a normal vitamin D level and normal calcium intake, urinary calcium < 100 mg/day and fractional excretion of calcium < 0.01 (fractional excretion of calcium = (urine calcium × serum creatinine)/(serum calcium × urine creatinine) suggests FHH.

    3. Serum magnesium is often increased in FHH.

    4. Genetic testing is available when the diagnosis is difficult to make.


Treatment for FHH is not necessary because the hypercalcemia is mild and only very rarely leads to complications.

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