What laboratory finding is typically associated with familial hypocalciuric hypercalcemia?

Familial hypocalciuric hypercalcemia is a genetic condition characterized by elevated levels of calcium in the blood (hypercalcemia) and low levels of calcium in the urine. This condition arises due to a mutation in the calcium-sensing receptor that leads to an abnormality in how the body regulates calcium levels.

The correct association with familial hypocalciuric hypercalcemia is hypophosphatemia. This occurs because hypercalcemia can lead to a reduced reabsorption of phosphate in the kidneys, resulting in lower phosphate levels in the serum. This sets up an imbalance, as higher calcium levels can inhibit the reabsorption of phosphate, thereby causing hypophosphatemia.

The other choices stem from conditions that do not align with the pathophysiology of familial hypocalciuric hypercalcemia. For example, hypercalciuria, which implies an excess of calcium in the urine, would be expected in conditions where calcium is excreted excessively; however, in this disorder, urinary calcium excretion is typically low. Similarly, hypomagnesemia and hypocalcemia do not fit the clinical picture of this condition, which primarily features elevated serum calcium levels.