Concomitant occurrence of Gitelman and Bartter syndromes in the same family?

The molecular defects responsible for the two most-common forms of inherited normotensive hypokalemic metabolic alkalosis have recently been defined. Most patients with Bartter syndrome have defects in transporters in the thick ascending limb of the loop of Henle, such as the Na-K-2Cl cotransporter, NKCC2, or the ATP-sensitive potassium channel, ROMK. Patients with Gitelman syndrome usually have mutations in the thiazide-sensitive Na-Cl cotransporter in the distal convoluted tubule. The location of the affected transporters correlates well with the typical presentation of these syndromes. Patients with Bartter syndrome typically present with normal or increased calcium excretion. Hypomagnesemia is present in only one-third of affected individuals. In contrast, hypomagnesemia and hypocalciuria are considered hallmarks of Gitelman syndrome. This report describes siblings presenting as young adults with mild symptoms associated with normotensive hypokalemic metabolic alkalosis. One sibling has hypocalciuria and hypomagnesemia, consistent with Gitelman syndrome. Surprisingly, the other sibling has normal serum magnesium and urinary calcium excretion. These siblings demonstrate the biochemical heterogeneity that can exist in patients with normotensive hypokalemic metabolic alkalosis. This report indicates that hypocalciuria does not always distinguish Gitelman and Bartter syndromes.