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February 1980

Supranormal 25-Hydroxyvitamin D and Subnormal 1,25-Dihydroxyvitamin D: Their Role in X-linked Hypophosphatemic Rickets

Author Affiliations

From the Departments of Pediatrics (Dr Chesney), Radiology (Mr Rose and Dr Mazess), and Biochemistry (Dr DeLuca and Mr Hamstra), the University of Wisconsin Center for Health Sciences, Madison, Wis; the College of Agricultural and Life Sciences (Dr DeLuca and Mr Hamstra), Madison, Wis.

Am J Dis Child. 1980;134(2):140-143. doi:10.1001/archpedi.1980.02130140014005

• Serum 25-hydroxyvitamin D (25-OH-D) and 1,25-dihydroxyvitamin D (1,25-(OH)2D) and bone mineral content by the photon-absorption technique were determined in eight patients with X-linked hypophosphatemic rickets treated for at least 24 months with oral sodium phosphate and high-dosage ergocalciferol (vitamin D2). Mean 25-OH-D2 level was 129.5 ± 67.5 ng/mL (mean ± SD); the level of 25-OH-D3 was 10.5 ± 5.8 ng/mL. These values were significantly higher than in normal subjects (total 25-OH-D mean of 27 ± 10 ng/mL). Serum 1,25-(OH)2D was 16.9 ± 8.5 pg/ml (mean ± SD) in the eight patients, significantly lower than 47 ± 16 pg/mL in 27 age-matched controls. Values indicative of significant demineralization were found in seven of the eight phosphate-treated patients, who had no radiologic evidence of rickets. These results suggest that any theory of the pathogenesis of this disorder must account for inappropriate renal vitamin D metabolism and for renal hyperphosphaturia. The failure of high-dosage oral phosphate and ergocalciferol to fully correct demineralization may suggest a role for calcitriol (1,25-(OH)2D3) as a therapeutic agent.

(Am J Dis Child 134:140-143, 1980)

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