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Vitamin D metabolism and bone mineralization in children with juvenile rheumatoid arthritis
L Hillman1, J T Cassidy, L Johnson
1Department of Child Health and Internal Medicine, University of Missouri-Columbia School of Medicine.
Insights
Children with juvenile rheumatoid arthritis (JRA) exhibit decreased bone mineralization due to low bone turnover. This study investigates bone health in JRA patients, finding reduced bone mineral content and altered bone metabolism markers.
Area of Science:
- Pediatric Rheumatology
- Pediatric Endocrinology
- Bone Metabolism
Background:
- Juvenile rheumatoid arthritis (JRA) is a chronic inflammatory condition affecting children.
- Bone health is a significant concern in pediatric rheumatic diseases, with potential for impaired growth and development.
- Understanding bone mineralization in JRA is crucial for managing long-term skeletal health.
Purpose of the Study:
- To assess bone mineralization and bone mineral content in a cohort of children diagnosed with JRA.
- To compare bone health parameters between children with JRA and healthy controls.
- To investigate potential mechanisms underlying altered bone metabolism in JRA.
Main Methods:
- Cross-sectional study involving 44 children with JRA and 37 age-matched healthy controls.
- Bone mineral content measured using single-photon absorptiometry.
- Analysis of serum and urinary markers including minerals, vitamin D metabolites, parathyroid hormone, and bone turnover markers (osteocalcin, bone alkaline phosphatase, tartrate-resistant acid phosphatase).
Main Results:
- Children with JRA demonstrated significantly lower bone mineral content compared to controls.
- Reduced serum concentrations of osteocalcin and bone alkaline phosphatase indicated decreased bone formation.
- Lower tartrate-resistant acid phosphatase and urinary calcium/creatinine ratios suggested diminished bone resorption.
- Serum calcium and parathyroid hormone levels were lower in JRA patients, while 1,25-dihydroxyvitamin D levels remained normal.
Conclusions:
- Decreased bone mineralization in JRA appears linked to a state of low bone turnover.
- The parathyroid hormone and 1,25-dihydroxyvitamin D levels may be inappropriately normal in the context of reduced serum calcium in children with JRA.
- These findings highlight the complex interplay of factors affecting bone health in pediatric rheumatoid arthritis.
Objective:
To examine bone mineralization and bone mineral content in a cross-sectional population of children with juvenile rheumatoid arthritis (JRA).
Methods:
Bone mineral content was measured by single-photon absorptiometry in 44 children with JRA and 37 control children. Serum concentrations of minerals, vitamin D, parathyroid hormone, osteocalcin, bone alkaline phosphatase, and tartrate-resistant acid phosphatase, 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 micrograms/L) and bone alkaline phosphatase (78.8 +/- 36.4 vs 123.0 +/- 46.0 IU/L) suggested reduced bone formation; lower levels of tartrate-resistant acid phosphatase (10.3 +/- 4.1 vs 14.4 +/- 5.8 IU/L) and a lower urinary calcium/creatinine ratio (0.07 +/- 0.06 vs 0.12 +/- 0.09) suggested decreased bone resorption. The serum calcium concentration was significantly lower (9.3 +/- 1.0 vs 10.0 +/- 0.4 mg/dl), as was the parathyroid 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 normal.
Conclusion:
These data suggest that decreased mineralization in JRA is related to low bone turnover; parathyroid hormone and 1,25-dihydroxyvitamin D levels may be inappropriately normal for the decreased serum calcium concentration in children with JRA.