Actions of 1,25-Dihydroxycholecalciferol in Patients with Hypophosphatemic, Vitamin-D-Resistant Rickets

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Abstract
1,25-dihydroxycholecalciferol, the active form of vitamin D, was administered orally in doses of 1.3 to 2.7 μg per day to four patients with hypophosphatemic, vitamin-D-resistant rickets to assess whether deficient production of this steroid might be responsible for this disorder. One patient was from a kindred with X-linked, dominant transmission, and two were from a family showing autosomal dominant transmission. The patients responded with increased urinary calcium, decreased fecal calcium or augmented intestinal absorption of radioactive calcium (47Ca). Urinary excretion of phosphorus decreased only slightly and transiently in two patients and increased in the other two; the hypophosphatemia was not corrected. Thus, a physiologic response in the intestinal absorption of calcium occurred, but the defect in renal tubular reabsorption of phosphate was not corrected. These observations provide evidence that the biochemical alterations in hypophosphatemic vitamin-D-resistant rickets are not due to impaired synthesis or action of 1,25-dihydroxycholecalciferol. (N Engl J Med 289:495–498, 1973)
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