Given that mutations in the Ncc gene were identified as the cause of Gitelman syndrome (19), it was expected that the knockout (KO) of this gene (Ncc-KO) would cause the changes observed in patients with this syndrome, namely, decreased extracellular volume with mild arterial hypotension, hypokalemia, metabolic alkalosis, hypocalciuria, and hypomagnesemia. The gene discussed is SLC12A3; the disease is familial primary hypomagnesemia.