Bone Modulating Factors in Nephrotic Children with Normal Glomerular Filtration Rate

Factors influencing bone and mineral metabolism were evaluated in 16 children with active nephrotic syndrome and normal glomerular filtration rate. All patients were proteinuric and/or hypoalbuminemic and had elevated serum triglyceride and cholesterol levels. Seven patients had never received or had discontinued glucocorticoid treatment at least 6 months before the study; six patients were receiving prednisone at the time of study. Although all patients were hypocalcemic (serum total or ionized calcium), none was hypomagnesemic. Despite the low serum calcium levels, circulating immunoreactive parathyroid hormone was elevated in only nine of 16. Plasma 25-hydroxyvitamin D was low in all 16 patients, averaging 7.6 ± 1.2 ng/mL for the group. In contrast, levels of 1,25-dihydroxyvitamin D were normal in 12 of 14 patients. Bone mineral content measured by photon absorptiometry averaged 83% and was less than 90% of normal in six of nine patients tested. The findings were not influenced by the recent or concurrent administration of glucocorticoid. The data demonstrate abnormalities of mineral and bone modulation in nephrotic children even in the absence of impaired glomerular filtration rate and irrespective of glucocorticoid therapy. The decrease in serum ionized calcium may be related to an absolute deficiency in 25-hydroxyvitamin D and/or a relative deficiency in 1,25-dihydroxyvitamin D. Undermineralization of bone may result from the low levels of vitamin D metabolites and, in some patients, from an increase in immunoreactive parathyroid hormone. Whether treatment with vitamin D metabolites and/or calcium supplementation will prevent the abnormalities remains to be demonstrated.