VITAMIN D-resistant rickets of the "simple" type is one of the most commonly encountered forms of metabolic bone disease in modern pediatric practice. In this disorder, rickets similar to that due to vitamin D deficiency develops in the face of usually adequate amounts of vitamin D and heals only with massive and sustained doses of the vitamin. Biochemically, the cardinal abnormality is hypophosphatemia, apparently the result of diminished tubular reabsorption of phosphate from the glomerular filtrate. Whether the renal abnormality is based upon a primary defect within the tubule cell or is a secondary effect, as for example from secondary hyperparathyroidism, is not yet known.
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