Abstract
The mineralization defect in vitamin D deficiency (animal model) results in decreased turnover of osteocalcin, a unique vitamin K-dependent calcium-binding protein of bone matrix. GLA is the modified glutamate residue that is excreted quantitatively after osteocalcin degradation. To determine whether a similar effect occurs in mendelian rachitic disorders of man, we assayed urinary content of GLA. We studied 11 XLH patients (5M, 6F) treated with calcitriol (1,25-(OH)2D3) and phosphate. Urinary GLA excretion (50±15(SD) μmol/g creat) was not different from normal (44±11 μmol/g creat, n=63). We compared GLA excretion in 5 ARVDD patients in a vitamin D-depleted state with 7 ARVDD patients receiving a therapeutic dose of 1,25-(OH)2D3 (1.0-1.5 μg/day). GLA excretion in the D-depleted ARVDD group was significantly lower than normal (31±6 μmol/g creat, p=.006). GLA excretion was higher in the 1,25-(OH)2D3 treated group (44±4 μmol/g creat, p < .001) and not different from controls. These observations suggest that osteocalcin turnover is decreased in untreated individuals with impaired mineral metabolism. GLA excretion appears to be a useful marker for turnover of bone matrix in disorders of mineralization.
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Cole, D., Reade, T., Lian, J. et al. 1111 URINARY EXCRETION OF γ-CARBOXYGLUTAMIC ACID (GLA) IN X-LINKED HYPOPHOSPHATEMIA (XLH) AND AUTOSOMAL RECESSIVE VITAMIN D DEPENDENCY (ARVDD). Pediatr Res 15 (Suppl 4), 628 (1981). https://doi.org/10.1203/00006450-198104001-01137
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DOI: https://doi.org/10.1203/00006450-198104001-01137