Rare benign disorder due to loss of function mutations in the calcium-sensing receptor (CASR) gene.
24 hour urine calcium on a normal calcium diet is usually very low at less than 100 mg, with the calcium-to-creatinine clearance ratio of less than 0.010.
Frequently associated with a positive family history and patients may have hypercalcemia at birth.
Almost all patients develop hypercalcemia by the third decade.