Distal nephron function in familial hypokalemia-hypomagnesemia (Gitelman's syndrome)

Hereditary disorders of potassium homeostasis

There has been a dramatic recent increase in the understanding of the renal epithelial transport systems with the identification, cloning and characterization of a large number of membrane transport proteins. The aim of this chapter is to integrate this body of knowledge with the understanding of the clinical disorders that accompany gain, loss or dysregulation of function of these transport systems. The specific focus is on the best-defined human clinical syndromes in which there are derangements in potassium (K(+)) homeostasis. The focus is on inherited syndromes, rather than on acquired syndromes due to tubular transport defects, and the therapeutic approaches address chronic derangements of K(+) homeostasis rather than acute interventions directed at life-threatening hyperkalaemia.

Renal genetic disorders related to K+ and Mg2+

The recent knowledge of the renal epithelial transport systems has exploded with the identification, cloning, and characterization of a large number of membrane transport proteins. The fundamental aspects of these transporters are beginning to emerge at the molecular level and are summarized in the accompanying contributions in this volume of the Annual Review of Physiology. The aim of my review is to integrate this body of knowledge with the understanding of the clinical disorders of human mineral homeostasis that accompany gain, loss, or dysregulation of function of these transport systems. The specific focus is on the best defined human clinical syndromes in which there are derangements in K(+) and Mg(2+) homeostasis.

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.