Almost all cases of Rett Syndrome are thought to be caused by mutations of the methyl CpG binding protein 2 (MECP2 gene). This gene holds instructions for the synthesis of a protein (methyl cytosine binding protein 2). The synthesis of this protein is needed for brain development and gene expression. In females with Rett Syndrome the mutation of the MECP2 gene causes insufficient amounts or abnormal proteins to be made and this causes genes to be abnormally expressed. Researchers are trying to find out if anything else causes this disorder. (NIH, 2009)