Familial hypocalciuric hypercalcemia is a genetic disorder that results in high calcium levels due to a mutation in the calcium-sensing receptor gene. In most cases the condition may be completely asymptomatic and go unnoticed throughout life, requiring no treatment. Familial hypocalciuric hypercalcemia is sometimes also referred to as familial benign hypercalcemia and may require genetic or other testing to differentiate between it and primary hyperparathyroidism, which more commonly causes raised calcium levels.
Due to the mutation in the calcium-sensing receptor gene in patients with familial hypocalciuric hypercalcemia, the body thinks that calcium levels are low and increases calcium in the blood. This is referred to as hypercalcemia. Normally, if the blood levels of calcium increase, the urinary output of calcium is also increased but, in the case of familial hypocalciuric hypercalcemia, this does not hold true and the urinary levels of calcium tends to be low, which is called hypocalciuria.
The parathyroid gland is an important player in the sensitive feedback mechanisms involved in the calcium balance of the body and, in the case of primary hyperparathyroidism, the parathyroid hormone levels tend to be high. In the case of familial hypocalciuric hypercalcemia, however, the levels of parathyroid hormone may be slightly raised, or at normal levels. The differentiation between primary hyperparathyroidism and familial hypocalciuric hypercalcemia will be made by using a number of tests which may include genetic testing and a 24-hour urine calcium test.
A 24-hour calcium urine test is done by collecting the urine over 24 hours. Usually the process recommended is that the first urination of the morning is done in the toilet and all urine thereafter is collected in the specific collection container obtained from the lab. This is continued until the next morning, when the first urination is also collected in the bottle. The amount of calcium is then measured and low or high levels of calcium excretion in the urine can be determined.
Genetic testing is done by PCR and DNA sequencing on a blood sample. The results of this test may only be obtained from the lab after 14 to 21 days. The diagnosis of familial hypocalciuric hypercalcemia, and differentiation between other conditions which may cause high calcium levels is important to ensure the correct treatment. In the case of primary hyperparathyroidism, a parathyroidectomy, or removal of the gland, may be necessary. In patients with familial hypocalciuric hypercalcemia, this is not normally recommended.