MON-193 RENAL TRANSPLANTATION IN A PATIENT WITH FAMILIAL SYNDROME OF HYPOCALCEMIA WITH HYPERCALCIURIA

Abstract

The calcium sensing receptor regulates the secretion of parathyroid hormone in response to changes in the extracellular calcium concentration and mutations that result in gain of function of this receptor are associated with with familial hypocalcemia with hypercalciuria. The high urinary calcium excretion leads to nephrocalcinosis and renal insufficiency. We present a case of a patient with end stage kidney disease due to nephrocalcinosis from familial hypocalcemia with hypercalciuria, who subsequently underwent renal transplantation with complete resolution of hypercalciuria. This is the first reported case of renal transplantation in a patient with familial hypocalcemic hypercalciuria. Case report: 58 year old female developed end stage kidney disease due to nephrocalcinosis. Nephrocalcinosis was secondary to familial hypoparathyroidism and she had known mutations in calcium sensing receptors and hence chronic hypocalcemia (1.8-1.9mmol/l) and hypercalciuria( 3.2mmol/l) . She subsequently underwent non directed living donor transplantation. Within 1 week after renal transplantation the urinary calcium concentration was measured and this was completely within normal limits with urine calcium concentration of 1 mmol/l and calcium/creatinine ratio of 0.29 ( normal range 0.06- 0.45mole ratio). Subsequent urine calcium concentrations are less than 0.20mmol/l and her graft function remains excellent. Discussion: This is the first case report of successful renal transplantation in a case of familial hypoparathyroidism with known gain of function or activating mutation of calcium sensing receptor which results in hypocalcemia and hypercalciuria. The calcium sensing receptor gene is expressed in the parathyroid glands and kidneys . This receptor regulates the the secretion of parathyroid hormone and reabsorption of calcium by the renal tubules in response to alterations of serum calcium levels. Gain of function mutation of the calcium sensing receptor gene will suppress the parathyroid hormone and increase the excretion of urinary calcium at inappropriately low serum calcium levels. The high urinary calcium concentration drives polyuria and dehydration and hence subsequently leads to nephrocalcinosis and renal insufficiency. With renal transplantation, we are essential replacing the affected abnormal calcium sensing receptors with normal calcium sensing receptor and hence normalising urinary calcium, thereby eliminating the risk of nephrocalcinosis in the graft. Conclusions: Renal transplantation is a safe and effective way of treating end stage kidney disease in patients with nephrocalcinosis due to familial hypocalcemia and hypercalciuria.