VITAMIN-D METABOLISM AND BONE MINERALIZATION IN CHILDREN WITH JUVENILE RHEUMATOID-ARTHRITIS

Objective: To examine bone mineralization and bone mineral content in a cross-sectional population of children with juvenile rheumatoid arth ritis (JRA). Methods: Bone mineral content was measured by single-phot on absorptiometry in 44 children with JRA and 37 control children. Ser um concentrations of minerals, vitamin D, parathyroid hormone, osteoca lcin, bone alkaline phosphatase, and tartrate-resistant acid phosphata se, and urinary concentrations of minerals, were determined. Results: Bone mineral content was decreased in children with JRA. Significantly lower concentrations of osteocalcin (7.4 +/- 3.4 vs 12.5 +/- 2.5 mu g /L) and bone alkaline phosphatase (78.8 +/- 36.4 vs 123.0 +/- 46.0 IU/ L) suggested reduced bone formation; lower levels of tartrate-resistan t acid phosphatase (10.3 +/- 4.1 vs 14.4 +/- 5.8 IU/L) and a lower uri nary calcium/creatinine ratio (0.07 +/- 0.06 vs 0.12 +/- 0.09) suggest ed decreased bone resorption. The serum calcium concentration was sign ificantly lower (9.3 +/- 1.0 vs 10.0 +/- 0.4 mg/dl), as was the parath yroid hormone concentration (19.8 +/- 8.6 vs 26.7 +/- 9.3 ng/L); 1,25- dihydroxyvitamin D values (30.1 +/- 10.5 vs 30.4 +/- 9.3 pg/ml) were n ormal. Conclusion: These data suggest that decreased mineralization in JRA is related to low bone turnover; parathyroid hormone and 1,25-dih ydroxyvitamin D levels may be inappropriately normal for the decreased serum calcium concentration in children with JRA.