MON-492 A Case of Gitelman’s Syndrome with Hyperphosphatemia That Responded Effectively to Single Oral Administration of Magnesium Oxide

Introduction: The course of Gitelman’s syndrome (GS) is characterized by metabolic alkalosis, hypokalemia, hypomagnesemia, and hypocalciuria (1). However, the involvement of this electrolyte imbalance of GS in parathyroid hormone action has not been determined. Clinical Case: A 34-year-old woman was admitted to hospital with muscle weakness and tetany/seizures caused by electrolyte imbalance. She had hyperphosphatemia (2.0 mmol/l) and hypocalciuric hypocalcemia (1.3 mmol/l, Fractional excretion of Ca 0.4%) in addition to severe hypomagnesemia (0.3 mmol/l) and hypokalemia (2.9 mmol/l) without metabolic alkalosis. The clinical diagnosis of GS was made on the basis of these laboratory data that was confirmed by gene test. We identified two heterozygous mutations in the SLC12A3 gene in this case (c.1732G>A, p.Val578Met and c.2537_38delTT, p.846fs) by targeted sequence for all causative genes of salt-losing tubulopathies. From these results, hypocalcemia and hyperphosphatemia were suggested to be caused by the secondary obstruction of appropriate parathyroid hormone release following severe hypomagnesemia. As we expected, single oral administration of magnesium oxide improved any electrolyte imbalance, including hypocalcemia and hyperphosphatemia of this case, and eliminated her symptoms. Conclusion: These observations in this unusual case suggest that even severe hypomagnesemia caused by GS was associated with resistance to appropriate parathyroid hormone secretion. This case reminded us the important message that secondary hypoparathyroidism can be caused by severe hypomagnesemia even in GS. References: (1) Blanchard A, Bockenhauer D, Bolignano D, Calò LA, et al: Gitelman syndrome: consensus and guidance from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference. Kidney Int. 2017;91;24-33.