Part of “CHAPTER 58 – PRIMARY HYPERPARATHYROIDISM“

FHH is a benign disorder associated with hypercalcemia.113 Differentiating individuals with FHH from those with primary hyperparathyroidism is extremely difficult. This disorder is a familial disease that has an autosomal dominant pattern of transmission. Penetrance is high, and the hypercalcemia often manifests in affected individuals in childhood. The disease is characterized by hypercalcemia and relative hypocalciuria. The hypocalciuria may be marked, but it is not absolutely discriminatory when compared with urinary calcium levels in patients with primary hyperparathyroidism. Subtotal parathyroidectomy does not cure the hypercalcemia. Laboratory findings for patients with FHH include mild hypercalcemia but normal serum levels of phosphate and 1,25(OH)₂D. The PTH concentration is usually normal, although in several cases, it has been elevated. The serum magnesium concentration is normal to moderately elevated. Typically, the renal calcium clearance/creatinine clearance ratio is <0.01. Family screening is often necessary to differentiate FHH from primary hyperparathyroidism.