[Biological and bone histomorphometric studies in hypophosphatemic vitamin-resistant rickets treated with 1,25-(OH)2D...

Five children aged 6 to 15 years were studied. They presented all the biological signs of hypophosphatemic vitamin resistant rickets: normal calcemia, hypophosphatemia, decrease in phosphorus Tm and normal PTH plasma level. Two children had never been given vitamin D treatment previously. The 1.25 (OH)2D has been given in 4 doses a day, to a total of 1 microgram/day, for one year. Phosphate was administered for the same time, doses varying from 40 to 150 mg/kg/day. Bone biopsies were performed at the onset and the end of treatment. Normal growth concerning bone age was observed in 3 cases. In the two others, growth remained disturbed. Radiological recovery was observed in all cases. Treatment induced and increase in serum phosphate. Tm PO4/FG remained lower than normal and even decreased during treatment. After one year of treatment, the osteoid volumes and surfaces decreased in all cases but did not always return to normal. The thickness index of osteoid and the speed of calcification were improved in 4 cases and worsened in the 5th. In two previously untreated patients an increase in plasma PTH and in the osteoclastic surface of resorption were observed on the bone biopsy during treatment.