Two types of nutritional rickets in infants

In 100 infants with nutritional rickets, i.e.. responsive to vitamin D therapy, we found a close inverse relationship between serum phosphorus. on the one hand, and serum alkaline phosphatase and the presence of radiological signs of rickets, on the other. There was no correlation between serum calcium and the severity of bone lesions. It is concluded that hypophosphatemia but not hypocalcemia is typical of rickets. Since hypophosphatemia and rickets can be produced experimentally by phosphate deficiency alone, we suggest our infants can be divided into two groups. one with true vitamin D deficiency that leads to hypocalcemia and no or mild bone lesions, and one with primary phosphate deficiency, resulting perhaps from a defect in phosphate transport, which leads to rickets and hypophosphatemia. Am. J. C/in. .Vutr. 29: 1222- 1226, 1976, Hurwitz et al. (I) observed in rats that a normal calcium (Ca) diet without vitamin D caused hypocalcemia and a small drop in bone ash, with no evidence of rickets, while a low phosphorus (P) diet with added vitamin D caused hypophosphatemia and severe bone lesions. These findings were simi- lar to our clinical observation that infants with hypocalcemia and tetany had very mild or no bone lesions on radiological examina- tion, while infants with severe rachitic bone lesions had low P and normal Ca values in the serum. It is worth noting that according to Steendijk (2) the primary Haversian systems of infant bones are similar to those of rat bones. The above considerations led us to investi- gate the relationship between the severity of the rachitic process, as expressed by the level of serum alkaline phosphatase (SAP) and the radiological picture of the bones on the one hand, with serum Ca and P levels, on the other.