Finally, because little is understood about iron loading and unloading at the cellular and molecular level, we propose to perform tissue microarray analysis on liver biopsy samples obtained from children with iron overload. This powerful tool will help identify over- and under-expressed genes in the clinical scenario of iron loading, and later in the setting of iron mobilization in these overloaded patients. This pilot study will allow us to investigate differences in gene expression from patients with mild, moderate and severe iron overload, as determined by quantitative LIC on liver biopsy. Our approach will allow characterization of gene expression and analysis for patterns that reflect cellular responses to different degrees of iron overload. This study will not obtain "normal liver" controls from our population, since sickle cell patients without transfusional iron overload have no clinical indication for liver biopsy. It is hoped, however, that subsequent therapeutic protocols will also include microarray studies on liver biopsy samples. In this way, the current microarray analysis will serve as a "baseline" and patients will serve as their own controls for differences in gene expression. This will particularly be important for those patients undergoing successful chelation therapy that should lower LIC. Overall, an understanding of the genetic and biochemical events that regulate these iron loading and unloading processes could greatly improve our ability to treat patients appropriately.