Severe hypomagnesaemia-induced hypocalcaemia in a patient with Gitelman's syndrome

Gitelman's syndrome (GS) is characterized by hyperreninaemic hyperaldosteronism, hypokalaemia, metabolic alkalosis, hypomagnesaemia and hypocalciuria and is due to a defect of the Na-Cl cotransporter at the distal tubule, which may appear in a sporadic or in a familial form. It is an autosomal recessive disorder associated with normal or reduced blood pressure. We report a case of severe hypomagnesaemia-induced hypocalcaemia in a 39-year-old Caucasian woman with GS. The patient had impaired parathormone (PTH) responsiveness to peripheral stimuli, as proved by the marked PTH increase and normalization of plasma calcium levels after acute and chronic administration of magnesium salts. Secondary normotensive hyperreninaemic hyperaldosteronism with hypokalaemia and metabolic alkalosis was also present. Normal plasma renin activity (PRA) and aldosterone levels were restored by administration of an inhibitor of prostaglandin synthesis. The electrolyte imbalance was successfully corrected with chronic treatment with magnesium and potassium salts. Genetic analysis identified a compound heterozygous mutation in the Na-Cl cotransporter gene (NCCT), confirming the diagnosis of GS. The striking feature of this case of GS was impaired PTH responsiveness to peripheral stimuli determined by hypomagnesaemia and the resulting severe hypocalcaemia, which had not previously been described in this syndrome.