Bone Disease in Thalassemia: A Molecular and Clinical Overview

Thalassemia bone disease is a common and severe complication of thalassemia-an inherited blood disorder due to mutations in the α or β hemoglobin gene. In its more severe form, severe anemia is present, and treatment with frequent red blood cell transfusion is necessary. Because the body has limited capacity to excrete iron, concomitant iron chelation is required to prevent the complications of iron overload. The effects of chronic anemia and iron overload can lead to multiple end-organ complications such as cardiomyopathy, increased risks of blood-borne diseases, and liver, pituitary, and bone disease. However, our understanding of thalassemia bone disease is incomplete and is composed of a complex piecemeal of risk factors that include genetic factors, hormonal deficiency, marrow expansion, skeletal dysmorphism, iron toxicity, chelators, and increased bone turnover. The high prevalence of bone disease in transfusion-dependent thalassemia is seen in both younger and older patients as life expectancy continues to improve. Indeed, hypogonadism and GH deficiency contribute to a failure to achieve peak bone mass in this group. The contribution of kidney dysfunction to bone disease in thalassemia is a new and significant complication. This coincides with studies confirming an increase in kidney stones and associated accelerated bone loss in the thalassemia cohort. However, multiple factors are also associated with reduced bone mineral density and include marrow expansion, iron toxicity, iron chelators, increased bone turnover, GH deficiency, and hypogonadism. Thalassemia bone disease is a composite of not only multiple hormonal deficiencies but also multiorgan diseases. This review will address the molecular mechanisms and clinical risk factors associated with thalassemia bone disease and the clinical implications for monitoring and treating this disorder.