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Bone Histomorphometry in Children and Adolescents with ß-Thalassemia Disease: Iron-Associated Focal Osteomalacia

Departments of Pediatrics (P.M., A.C.), Pathology (V.S., P.K.), Radiology (R.S.), and Medicine (S.D., R.R.), Research Center (L.C., A.S.), Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand

Address all correspondence and requests for reprints to: Dr. Pat Mahachoklertwattana, Department of Pediatrics, Ramathibodi Hospital, Faculty of Medicine, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand. E-mail: rapmw{at}mahidol.ac.th.

Thalassemia/hemoglobinopathy is a hereditary disease that causes chronic anemia and increased erythropoiesis. Consequently, an expansion of bone marrow spaces may contribute to osteopenia/osteoporosis. However, the pathogenesis of bone changes is not yet known. We, therefore, carried out the study on bone histomorphometry and biochemical and hormonal profiles in children and adolescents with suboptimally treated ß-thalassemia disease with the hope of gaining some new insight into the cellular and structural alterations of thalassemic bone. Seventeen patients underwent iliac crest bone biopsy for histomorphometric analyses. Bone mineral density (BMD) measurements were performed by dual energy x-ray absorptiometry. Most patients had growth retardation and delayed bone age. BMD was low especially at the lumbar spine. Serum IGF-I levels were almost always low. Bone histomorphometry revealed increased osteoid thickness, osteoid maturation time, and mineralization lag time, which indicate impaired bone matrix maturation and defective mineralization. In addition, iron deposits appeared along mineralization fronts and osteoid surfaces. Moreover, focal thickened osteoid seams were found together with focal iron deposits. Dynamic bone formation study revealed reduced bone formation rate. These findings indicate that delayed bone maturation and focal osteomalacia are the pathogenesis of bone disease in suboptimally blood-transfused thalassemics with iron overload. Iron deposits in bone and low circulating IGF-I levels may partly contribute to the above findings.

This work was supported by Thailand Research Fund.

Abbreviations: BA, Bone age; BAP, bone-specific alkaline phosphatase; BFR, bone formation rate relative to bone surface; BMD, bone mineral density; BS, bone surface; Ca, calcium; Cr, creatinine; CV, coefficient of variation; Dpd, deoxypyridinoline; ES/BS, eroded surface relative to bone surface; FeS, iron-stained bone surface; FT₄, free T₄; MAR, mineral apposition rate; OC, osteocalcin; 25-OHD, 25-hydroxyvitamin D; O.Th, osteoid thickness; P, phosphate; vBMD, volumetric bone mineral density.

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