Case report: familial hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia (FHH) is a hypercalcemic syndrome that is usually characterized by uncomplicated hypercalcemia and normal longevity. The inheritance pattern is autosomal dominant with high penetrance, and it affects both men and women equally. FHH is caused by mutations that disturb the normal functioning of the calcium-sensing receptor (CaSR) gene. This causes a general lack of sensitivity to calcium, eventually leading to hypercalcemia and low calcium levels in the urine.

We report a case of a healthy 24-year-old female with longstanding hypercalcemia and a family history indicating asymptomatic hypercalcemia. The patient was also asymptomatic and had no significant past medical or surgical history. Laboratory investigations and the genetic study revealed findings suggestive of FHH subtype 1.

The phenotype of FHH is normal, and symptoms of hypercalcemia are usually not present. Patients with FHH and hypoparathyroidism have lower calcium clearance than controls with hypoparathyroidism. This shows that relative hypocalciuria in FHH is not caused by hyperparathyroidism. Since calcium does not appropriately suppress or affect the parathyroid glands in FHH, this means that FHH is a disorder of abnormal transport of extracellular calcium and/or response to it in at least two organs, the parathyroid gland and the kidney. It is quite similar to primary hyperparathyroidism (pHPT) biochemically hence it is important to differentiate this condition from pHPT and hypercalcemia caused by other diseases to avoid any unnecessary surgical or medical intervention.