Cruz D, Simon D, Lifton R
Inactivating mutations in the Na-Cl cotransporter are
associated with high bone density
Am Soc Nephrol Ann Mtg -- Miami
J Am Soc Nephrol
(Sep) 10:597A 1999

Gitelman's syndrome (GS) is an autosomal recessive disorder
characterized by hypokalemia, metabolic alkalosis, hypomagnesemia
and hypocalciuria. It is caused by homozygous inactivating
mutations in the thiazide-sensitive Na-Cl co-transporter gene
(NCCT), and results in hypocalciuria analogous to that
produced by thiazide diuretics. NCCT is also expressed in human
osteoblast-like cell lines. Recent data support a direct effect
of thiazide diuretics on these cells. Chronic thiazide therapy
has been reported to improve bone mineral density (BMD) in
patients with osteoporosis and to reduce the incidence of hip
fractures.
To determine the effect of NCCT mutations on BMD, we
studied 18 GS patients, and 28 unaffected family members from 3
extended Gitelman's kindreds. The unaffected relatives were
classified as heterozygous for NCCT mutations (n=18), or
wild type (n=10). BMD was measured by DEXA. To control for
differences in age, sex and race, BMD Z-scores were evaluated.
Biochemical markers of bone turnover and calcium homeostasis were
measured. The 3 groups were compared using ANOVA.
BMD Z-scores | Affected | Heterozygote | Wild Type | P |
Spine | +1.31 ± 0.30 | +0.64 ±
0.22 | -0.22 ± 0.24 | 0.009 |
Femoral Neck | +0.68 ± 0.19 | +0.14 ±
0.21 | -0.36 ± 0.19 | 0.014 |
Total Hip | +0.86 ± 0.30 | +0.25 ±
0.17 | -0.38 ± 0.22 | 0.006 |
Total Body | +1.42 ± 0.79 | +1.09 ±
0.33 | -0.07 ± 0.37 | 0.079 |
Urine Ca/Cr | 0.18 ± 0.04 | 0.26 ±
0.03 | 0.34 ± 0.05 | 0.020 |
All subjects had normal serum calcium and phosphorus levels.
Dietary calcium intake, PTH, 1,25
(OH)2 vitamin D, osteocalcin, and urine
pyridinoline and deoxypyridinoline levels were similar in all
groups. These data indicate that the inactivation of the NCCT is
associated with a lower urinary calcium excretion, and a higher
BMD. Whether the latter reflects lifelong hypocalciuria or a
direct effect on osteoblasts remains to be determined.
Copyright © 1999 American Society of Nephrology