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.