Orphanet maintains the Orphanet nomenclature of rare diseases, essential in improving the visibility of rare diseases in health and research information systems: each disease in Orphanet is attributed a unique and stable identifier, the ORPHA number.
Orphanet uses the European definition of a rare disease, as defined by the European Union Regulation on Orphan Medicinal Products (1999), that being a disease that affects not more than 1 person per 2000 in the European population.
The Orphanet rare disease nomenclature is comprised of a heterogeneous typology of entities of decreasing extension, including: groups of disorders, disorders, sub-types. A disorder in the database can be a disease, a malformation syndrome, a clinical syndrome, a morphological or a biological anomaly or a particular clinical situation (in the course of a disorder). They are organised into groups, and further divided into clinical, etiological or histopathological sub-types.
The ORPHA number for pityriasis rubra pilaris is 2897. The following information is included when searching for ORPHA:2897.
✽   Prevalence: <1 / 1 000 000
✽   Inheritance: Autosomal dominant or Not applicable
✽   Age of onset: Infancy, Neonatal
✽   ICD-10: L44.0
✽   OMIM: 173200
✽   UMLS: C0032027
✽   MeSH: D010916
✽   GARD: 7401
✽   MedDRA: 10035116
Source:Â http://www.orpha.net/consor/cgi-bin/Disease_Search.php?lng=EN
