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July 1985

Vitamin D–Dependent Rickets-Reply

Author Affiliations

Division of Pediatric Nephrology The Children's Hospital of Pittsburgh 125 DeSoto St Pittsburgh, PA 15213

Am J Dis Child. 1985;139(7):651. doi:10.1001/archpedi.1985.02140090013008

In Reply.—We read Dr Özsoylu's comments with interest. There are a few findings in our patient that would distinguish her from vitamin D–dependent rickets type I. First, she had an elevated maximum reabsorption of phosphate/glomerular filtration rate in the presence of hyperphosphatemia and secondary hyperparathyroidism. This provides indirect evidence of renal nonresponsiveness. Most patients with secondary hyperparathyroidism and normal renal function manifest hypophosphatemia and phosphaturia as a result of the elevated parathyroid hormone levels!1 Patients with vitamin D-dependent rickets type I usually manifest a decrease in maximum reabsorption of phosphate/glomerular filtration rate, although some have normal values.2

Second, normal levels of vitamin D metabolites, particularly calcitriol, were demonstrated in the patient under consideration. This alone distinguishes her from vitamin D-dependent rickets type I where calcitriol levels are low and 25-hydroxychole-calciferol is either normal or high.

Third, the bone biopsy specimen in our patient was consistent with osteitis fibrosa