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Bone disease in children with homozygous beta-thalassemia
L Rioja1, R Girot, M Garabédian
1CNRS URA.583-Université Paris V, Department of Hematology, Hôpital des Enfants-Malades, Paris, France.
Insights
Thalassemic bone disease in children shows severe cortical changes, not typically linked to iron overload or vitamin D deficiency. Bone marrow hyperactivity appears to be the primary cause of these skeletal alterations.
Area of Science:
- Hematology
- Bone Biology
- Pediatric Endocrinology
Background:
- Thalassemic bone disease pathogenesis is not fully understood.
- The roles of bone marrow hyperactivity, iron overload, and vitamin D deficiency are unclear.
- Severe skeletal changes are common in transfusion-dependent beta-thalassemia.
Purpose of the Study:
- To investigate the histological features of bone in children with beta-thalassemia.
- To determine the contribution of iron overload and vitamin D deficiency to thalassemic bone disease.
- To identify the underlying causes of skeletal complications in this patient group.
Main Methods:
- Analysis of iliac crest bone biopsies from 17 children with homozygous beta-thalassemia.
- Histochemical detection of iron deposits.
- Measurement of serum ferritin, plasma 25-hydroxyvitamin D (25(OH)D), calcium, phosphate, alkaline phosphatase, and parathyroid hormone levels.
- Comparison of vitamin D levels with age-matched controls.
Main Results:
- Severe cortical bone changes, including fissures and mineralization defects, were observed.
- Iron deposits were present in bone marrow and bone interfaces.
- Vitamin D levels were comparable to controls, and overt vitamin D deficiency was not evident.
- Hypocalcemia was present in some patients, but without clear signs of vitamin D deficiency.
Conclusions:
- Iron overload and vitamin D deficiency do not appear to be major contributors to thalassemic bone disease.
- Cortical bone lesions are likely a consequence of bone marrow hyperactivity.
- Further research into the mechanisms of marrow hyperactivity is warranted.
Abstract:
The histological features of thalassemic bone are imperfectly known, and the roles of bone marrow hyperactivity, iron overload or vitamin D deficiency in the pathogenesis of the disease are not clearly identified. In this study we examined iliac crest biopsies from 17 transfusion-dependent children with homozygous beta-thalassemia and severe radiological skeletal thalassemic changes, including widening of medullary spaces and osteoporosis. Rachitic lesions were not observed. Serum ferritin concentrations were increased in all but one subject. Iron deposits were histochemically detected in bone marrow, at the marrow-bone interface, along cement lines and mineralizing perimeters. Minor changes were present in trabecular bone, and osteomalacia was absent. By contrast, cortical bone exhibited severe changes including fissures and focal mineralization defects. Plasma 25-hydroxyvitamin D (25(OH)D) concentrations measured during the winter (December-May, 6.5 +/- 4.9 ng/ml, mean +/- SD, n = 6) and during the summer (June-November, 13.8 +/- 8.4 ng/ml, n = 9) did not differ from those of age-matched children living in the same country. Seven patients had moderate hypocalcemia but no biological signs suggestive of vitamin D deficiency: all had normal alkaline phosphatase activity, normal or slightly elevated plasma phosphate, only two had low plasma 25(OH)D concentrations and two others supranormal values of plasma immunoreactive parathyroid hormone. These results show that iron overload and vitamin D deficiency do not seem to play an important role in the pathogenesis of thalassemic bone disease, which is characterized by cortical lesions probably related to marrow hyperactivity.