Familial hypocalciuric hypercalcaemia is an autosomal dominant disease. The pathophysiology is due to a defective calcium receptor on the membranes of the parathyroid and renal tubular cells. This results in a decreased renal clearance of calcium, PTH is usually normal or increased, PO4 is usually decreased. Diagnosis is made on family history and determination of low urinary calcium clearance. Typically, the Fractional Excretion of Ca is <1%.