Studies were done to determine the cause for hypocalcemia, secondary hyperparathyroidism, osteomalacia and osteitis fibrosa cystica in a 22-year-old black woman. The patient had normal serum 25-hydroxyvitamin D (14 ng per milliliter) and markedly elevated serum 1,25-dihydroxyvitamin D (137 pg per milliliter). Vitamin D3, 4000 units per day for four weeks, increased the serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D to as high as 29 and 297 pg per milliliter, respectively, and corrected the hypocalcemia and secondary hyperparathyroidism. The results suggest that the disorder results from impaired end-organ response to 1,25-dihydroxyvitamin D. We propose that the entity be called vitamin-D-dependent rickets Type II. (N Engl J Med 298:996–999, 1978) VITAMIN-D-dependent rickets is characterized by clinical and biochemical features of rickets that occur despite an adequate intake of vitamin D and can be entirely reversed by pharmacologic doses of vitamin D.1 2 3 Recent evidence suggests that the basic abnormality is diminished renal synthesis of 1,25-dihydroxyvitamin D.1 2 3 Thus, patients with this disease have been shown to respond to small doses of 1,25-dihydroxyvitamin D31,2 or 1,α-hydroxyvitamin D3,3 and in one case, serum 1,25-dihydroxyvitamin D was found to be below the limits of detection by a binding assay.4 The patient with osteomalacia described below had hypocalcemia and secondary hyperparathyroidism in association.
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