Supranormal 25-hydroxyvitamin D and subnormal 1,25-dihydroxyvitamin D: their role in X-linked hypophosphatemic rickets
R. W. Chesney, R. B. Mazess, P. Rose, A. J. Hamstra and H. F. DeLuca
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 phsophate-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.
