What is a Rare Disease?

Rare DiseaseKey figures

There are over 300 million people living with one or more of over 6,000 identified rare diseases around the world1, each supported by family, friends and a team of carers that make up the rare disease community.

Each rare disease may only affect a handful of people, scattered around the world, but taken together the number of people directly affected is equivalent to the population of the world’s third largest country.

Rare diseases currently affect 3.5% - 5.9% of the worldwide population.

72% of rare diseases are genetic whilst others are the result of infections (bacterial or viral), allergies and environmental causes, or are degenerative and proliferative.

70% of those genetic rare diseases start in childhood.

  • A disease defined as rare in Europe when it affects fewer than 1 in 2,000 people.
  • A disease is defined as rare in the USA when it affects fewer than 200,000 Americans at any given time.

Characteristics of rare diseases

Over 6000 rare diseases are characterised by a broad diversity of disorders and symptoms that vary not only from disease to disease but also from patient to patient suffering from the same disease.

Relatively common symptoms can hide underlying rare diseases leading to misdiagnosis and delaying treatment. Quintessentially disabling, the patients quality of life is affected by the lack or loss of autonomy due to the chronic, progressive, degenerative, and frequently life-threatening aspects of the disease.

The fact that there are often no existing effective cures adds to the high level of pain and suffering endured by patients and their families.

Common chaellenges

The lack of scientific knowledge and quality information on the disease often results in a delay in diagnosis. Also the need for appropriate quality health care engenders inequalities and difficulties in access to treatment and care. This often results in heavy social and financial burdens on patients.

As mentioned, due to the broad diversity of disorders and relatively common symptoms which can hide underlying rare diseases, initial misdiagnosis is common. In addition, symptoms differ not only from disease to disease, but also from patient to patient suffering from the same disease.

Due to the rarity and diversity of rare diseases, research needs to be international to ensure that experts, researchers and clinicians are connected, that clinical trials are multinational and that patients can benefit from the pooling of resources across borders. Initiatives such as the European Reference Networks (networks of centres of expertise and healthcare providers that facilitate cross-border research and healthcare), the International Rare Disease Research Consortium and the EU Framework Programme for Research and Innovation Horizon 2020 support international, connected research.

How can Rare Disease Day make a difference?

Rare Disease Day raises awareness for the 300 million people living with rare disease around the world and their families and carers.

The long-term cause of the Rare Disease Day campaign is to achieve equitable access to diagnosis, treatment, health and social care and social opportunity for people affected by a rare disease.

Important progress continues to be made with joint international advocacy efforts for universal health coverage (UHC), part the United Nation’s Sustainable Development Goals (SGDs) to advocate for equitable health systems that meet the needs of people affected by rare diseases in order to leave no one behind.

Rare Disease Day is the opportunity advocate for rare diseases as a human rights priority at local, national and international level as we work towards a more inclusive society.

Rare Disease Day is a great example of how progress continues to be made, with events being held worldwide each year. Beginning in 2008, when events took place in just 18 countries, Rare Disease Day has taken place every year since, with events being held in over 100 countries in 2019.


1Research recently published in the European Journal of Human Genetics, article authored by EURORDIS-Rare Diseases Europe, Orphanet & Orphanet Ireland “Estimating cumulative point prevalence of rare diseases: analysis of the Orphanet database”. The analysis is of rare genetic diseases and is therefore conservative as it does not include rare cancers, nor rare diseases caused by rare bacterial or viral infectious diseases or poisonings https://www.nature.com/articles/s41431-019-0508-0

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