RGD uses the Human Disease Ontology (DO, https://disease-ontology.org/) for disease curation across species. RGD automatically downloads each new release of the ontology on a monthly basis. Some additional terms which are required for RGD's curation purposes but are not currently covered in the official version of DO have been added. As corresponding terms are added to DO, these custom terms are retired and the DO terms substituted in existing annotations and subsequently used for curation.
A non-Langerhans-cell histiocytosis is characterized as a benign skin lump or bump caused by a collection of cells called histiocytes. These may be red, orange or tan at first, but over time may become more yellow in color. These bumps usually appear on the head, neck and trunk. (DO)