Vitamin-D-resistant rickets: the effect of calcium infusion on phosphate reabsorption.

Vitamin D-resistant rickets (R.R.) is a genetically transmitted form of rickets that fails to respond to treatment with nutritional doses of vitamin D. I,t is characterized by a low serum phosphorus, a normal serum calcium, and an elevated serum alkaline phosphatase, and is transmitted by a sex-linked dominant inheritance pattern (2). In the first detailed study of R.R., Albright, Butler and Bloomberg (3) demonstrated poor intestinal absorption of calcium and hyperphosphaturia. Nutritional doses of vitamin D had no effect on these metabolic abnormalities, but massive doses improved calcium absorption and decreased the hyperphosphaturia.1 Albright and colleagues therefore suggested that the poor absorption of calcium was a stimulus for increased parathyroid hormone secretion, which in turn caused the hyperphosphaturia. In recent years, many studies of R.R. have demonstrated that the fraction of filtered phosphate reabsorbed (TRP) is low despite the presence of a low serum phosphorus concentration. Considering this finding and the similarity of R.R. to the Fanconi syndrome and renal glycosuria, Dent and Harris (4, 5), Fanconi (6) and others have concluded that R.R. is caused by an isolated renal tubular defect of phosphate reabsorption. This opinion has been widely accepted and has led to general usage of the term "phosphate diabetes" as a synonym for the disease.