An Operational Description of Rare Diseases aims to provide a common reference to improve the recognition of rare diseases within health systems and support the development of policies that address the challenges faced by Persons Living with a Rare Disease.
The description is part of RDI’s Memorandum of Understanding with the World Health Organization (WHO).

Improving health and social equity for Persons Living with a Rare Disease (PLWRD) and their families, is increasingly recognised as a global policy priority.
This commitment is expressed in the Political Declaration on Universal Health Coverage (2019) which includes mention of rare diseases and the UN Resolution on “Addressing the Challenges of Persons Living with a Rare Disease and their Families”, adopted in December 2022.
As public health agencies and governments at national, regional, and international levels develop and implement policies to support the rare disease community, they need a common reference.
The proposed Operational Description of rare diseases would describe what diseases are considered rare, how many persons are affected, and why the rare disease community demands specific attention and policy action.
The Description would describe:
- What diseases are considered rare
- How many persons are affected
- Why the rare disease community demands their specific attention.
The Operational Description will serve as a common point of reference to inform a wide range of stakeholders, including policymakers, and allow a baseline to monitor measurable change at local, national, and international levels.
Attempts to define rare diseases often prioritise disease prevalence thresholds and frequency; in contrast, an operational description would consider the specific clinical and qualitative challenges associated with the low prevalence of rare diseases.
A definition that recognizes the distinct challenges, burden, and impact on Persons Living with a Rare Disease, their families, health systems, and society.
RDI collaborates with a global panel of rare disease experts to propose an internationally recognised Operational Description of rare diseases composed of a core definition of rare diseases complemented by a descriptive framework.
Experts PANEL
Roberta Anido de Pena | Iberoamerican Alliance for Rare Diseases (ALIBER), Federación Argentina de Enfermedades Poco Frecuentes (FADEPOF), Argentina |
Diego Ardigò | Chiesi Pharmaceuticals, Italy |
Gareth Baynam | Rare Care- Clinical Centre of Expertise for Rare and Undiagnosed Diseases, Perth Children’s Hospital, Western Australia, Australia |
Hugh Dawkins | DA Precision Health, Australia |
Ada Hamosh | Johns Hopkins School of Medicine, Online Mendelian Inheritance in Man (OMIM), USA |
Robert Jakob | Health Statistics and Information Systems, World Health Organisation, Switzerland |
Eva Krpelanova | Health Statistics and Information Systems, World Health Organisation, Switzerland |
Yann Le Cam | EURORDIS – Rare Diseases Europe, France |
Helen Malherbe | Rare Diseases South Africa, South Africa |
Jane Millar | International Health Terminology Standards Development Organisation (IHTSDO), SNOMED International, UK |
Caron Molster | Office of Population Health Genomics, West Australia Department of Health, Australia |
Lucia Monaco | International Rare Diseases Research Consortium, Fondazione Telethon, Italy |
Carmencita Padilla | University of the Philippines Manila, Philippines |
Anne Pariser | National Center for Advancing Translational Sciences (NCATS), NIH, USA |
Ana Rath | Orphanet, INSERM, France |
Peter Robinson | The Jackson Laboratory, USA |
Franz Schaefer | ERKnet European Reference Network, Heidelberg University Hospital, Germany |
Stefanie Weber | Code Systems, Federal Institute for Drugs and Medical Devices (BfArM), Germany |
Key RESOURCES
- Orphanet – Portal for rare diseases and orphan drugs
- Nguengang Wakap S, Lambert DM, Olry A, et al. “Estimating cumulative point prevalence of rare diseases: analysis of the Orphanet database.”
- Haendel M, Vasilevsky N, Unni D, et al. “How many rare diseases are there?”
- Richter T, Nestler-Parr S, Babela R, et al. “Rare Disease Terminology and Definitions-A Systematic Global Review: Report of the ISPOR Rare Disease Special Interest Group.”
Additional references and documents will be included

For more information, contact, Mary Wang