Bone Disease in Children with Homozygous Beta-thalassemia

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.