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Inactivation of the Na‐Cl Co‐Transporter ( NCC ) Gene Is Associated With High BMD Through Both Renal and Bone Mechanisms: Analysis of Patients With Gitelman Syndrome and Ncc Null Mice
Author(s) -
NicoletBarousse Laurence,
Blanchard Anne,
Roux Christian,
Pietri Laurence,
BlochFaure May,
Kolta Sami,
Chappard Christine,
Geoffroy Valérie,
Morieux Caroline,
Jeunemaitre Xavier,
Shull Gary E,
Meneton Pierre,
Paillard Michel,
Houillier Pascal,
De Vernejoul MarieChristine
Publication year - 2005
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.041238
Subject(s) - gitelman syndrome , medicine , endocrinology , transporter , bone mineral , gene , osteoporosis , genetics , chemistry , biology , hypomagnesemia , organic chemistry , magnesium
Chronic thiazide treatment is associated with high BMD. We report that patients and mice with null mutations in the thiazide‐sensitive NaCl cotransporter (NCC) have higher renal tubular Ca reabsorption, higher BMD, and lower bone remodeling than controls, as well as abnormalities in Ca metabolism, mainly caused by Mg depletion. Introduction: Chronic thiazide treatment decreases urinary Ca excretion (UVCa) and increases BMD. To understand the underlying mechanisms, Ca and bone metabolism were studied in two models of genetic inactivation of the thiazide‐sensitive NaCl cotransporter (NCC): patients with Gitelman syndrome (GS) and Ncc knockout ( Ncc −/− ) mice. Materials and Methods: Ca metabolism was analyzed in GS patients and Ncc −/− mice under conditions of low dietary Ca. BMD was measured by DXA in patients and mice, and bone histomorphometry was analyzed in mice. Results: GS patients had low plasma Mg. They exhibited reduced UVCa, but similar serum Ca and GFR as control subjects, suggesting increased renal Ca reabsorption. Blood PTH was lower despite lower serum ionized Ca, and Mg repletion almost corrected both relative hypoparathyroidism and low UVCa. BMD was significantly increased in GS patients at both lumbar (+7%) and femoral (+16%) sites, and osteocalcin was reduced. In Ncc −/− mice, serum Ca and GFR were unchanged, but UVCa was reduced and PTH was elevated; Mg repletion largely corrected both abnormalities. Trabecular and cortical BMD were higher than in Ncc +/+ mice (+4% and +5%, respectively), and despite elevated PTH, were associated with higher cortical thickness and lower endosteal osteoclastic surface. Conclusions: Higher BMD is observed in GS patients and Ncc −/− mice. Relative hypoparathyroidism (human) and bone resistance to PTH (mice), mainly caused by Mg depletion, can explain the low bone remodeling and normal/low serum Ca despite increased renal Ca reabsorption.