Familial hypocalciuric hypercalcemia

Familial hypocalciuric hypercalcemia is a condition that can cause hypercalcemia.

Causes
Types include:

Most cases are associated with loss of function mutations in the CASR gene, which encodes a calcium-sensing receptor, expressed in parathyroid and kidney tissue. The perceived lack of calcium levels by the parathyroid leads to constiutely high levels of parathyroid hormone, and therefore hypercalcemia.

Another form has been associated with chromosome 3q.

Differential diagnosis
This condition is indicated by the presence of hypercalcemia (elevated levels of calcium in the blood) at the same time with hypocalciuria (low levels of calcium in the urine). (Usually elevated calcium levels in the blood are correlated with elevated calcium urine levels, as a properly sensing kidney works to excrete the mineral.) A family history could reinforce the diagnosis.

Treatment
No treatment is generally required, as bone demineralisation and kidney stones are relatively uncommon in the condition.

Functions of the Calcium-sensing Receptor

 * Parathyroid gland: mediates negative feedback mechanisms relating to PTH secretion (PTH secretion should decrease if there is a high blood calcium level). Abnormalities in the CASR here cause hypercalcaemia.
 * Kidneys: mediates negative feedback mechanisms relating to calcium reabsorption from the tubular system (reabsorption should decrease if there is a high blood calcium level). Abnormalities in the CASR here cause both hypercalcaemia and hypocalciuria.

Clinical features

 * Most cases: Asymptomatic (unlike primary hyperparathyroidism)
 * Hypercalcaemia
 * Hypocalciuria ( Ca excretion rate < 0.02 mmol/L).
 * Normal to high PTH (CaSR mutation causes the parathyroid glands to be less sensitive to serum calcium, resulting in normal to high PTH despite elevated serum calcium)
 * Hypermagnesaemia
 * Green colored urine