Serum parathyroid hormone in X-linked hypophosphatemia

Serum immunoreactive parathyroid hormone(IPTH) is normal in patients with X-linked hypophosphatemic rickets who are not treated with phosphate salts. Phosphate raises IPTH in these patients. Endogenous IPTH does not influence the existing defect in tubular reabsorption of phosphate in male patients.

Pathogenesis of rickets and osteomalacia in familial hypophosphataemia

Calcium and/or phosphate tolerance tests were performed on patients with familial hypophosphataemia, normal control subjects, and patients with vitamin D deficient osteomalacia. Intestinal calcium absorption was similar in patients with familial hypophosphataemia and control subjects. The phosphate tolerance test, which is known to be `flat' in patients with familial hypophosphataemia, was normal in patients with vitamin D deficient osteomalacia. These findings suggest that rickets and osteomalacia in familial and some cases of non-familial hypophosphataemia are unrelated to abnormal metabolism of vitamin D. This hypothesis is supported by the fact that intestinal calcium absorption as measured by calcium tolerance test is normal in familial hypophosphataemia. It is suggested that the primary abnormality in familial hypophosphataemia is a partial metabolic block in the intestinal absorption and renal tubular reabsorption of phosphate.

Metabolism of vitamin D3-3H in vitamin D-resistant rickets and familial hypophosphatemia

The fate of an intravenous dose of tritiated vitamin D(3) was studied in seven normal subjects, four children with vitamin D-resistant rickets, and four adults with a familial history of vitamin D-resistant rickets and persistent hypophosphatemia. An abnormal metabolism of vitamin D in vitamin D-resistant rickets was defined and characterized by a decrease in the plasma fractional turnover rate, a marked increase in plasma water-soluble metabolites, and a relative decrease in the conversion of vitamin D to a polar, biologically active metabolite. Alterations in vitamin D metabolism in the adults with persistent hypophosphatemia were similar but less severe than those of affected children with vitamin D-resistant rickets. It is tentatively concluded that the abnormalities in vitamin D metabolism documented in patients with vitamin D-resistant rickets and familial hypophosphatemia may account for the observed osseous and biochemical changes.