Erdheim-Chester disease (ECD) is a rare multisystemic disease characterized by the infiltration of multiple organs by foamy CD68 + CD1a- histiocytes (resident mononucleate macrophages) and “Touton” cells (multinucleated giant cells), which are typical of lesions with high lipid content, such as fat necrosis, xanthomas, and xanthelasmas. This evidence concerns the gene CD1A and Erdheim-Chester disease.