What is a rare disease?
1Rare yet common
A rare disease is one that affects fewer than 1 in 2,000 people.
There are over 7,000 rare diseases, and about 1-in-17 people will be affected by a rare condition at some point in life.
While rare diseases are individually rare, they are collectively common.
Why the zebra?
The rare disease community has adopted the zebra symbol. The old adage ‘Hear hooves? Think horses, not zebras’ — meaning that the most obvious cause or outcome is the most likely — is often used in medical training. But while you might assume that a rare disease is unlikely, the chances are higher than you might think. Always stay alert to the possibility of a rare disease. Always 'think rare'.
2Unique and different
Much like the term 'cancer', the term 'rare disease' is used as a catch-all term for thousands of conditions that differ greatly.
About 80% of rare diseases are caused by a variant in a person's genomic make up, which can either be inherited or arise for the first time in an individual.
About 70% of rare diseases present exclusively in children. Early diagnosis can help to prevent severe disability or even death, which is why newborn screening has been made a priority in the England Rare Diseases Action Plan.
It's also important not to overlook the 20% of rare diseases that are non-genomic. While many rare diseases are caused by changes in a person’s DNA, others have a different cause.
Scroll the infographics below to learn more about some of the different kinds of rare disease and their causes.
3Shared experience
Though rare diseases themselves differ greatly, the people affected by them describe similar experiences and challenges.
Understanding the lived experience specific to people with a condition that is rare is an important part of providing holistic care and support.
You cannot learn to recognise over 7,000 individual rare diseases, but you can learn to recognise the patterns suggestive of a rare condition and develop your understanding of the shared physical, emotional and psychological experiences of those who are affected.
Scroll through the images below to explore some of the experiences that people with rare conditions report. Visit our complementary resource, 'What is the diagnostic odyssey?', to learn more about the long journey to diagnosis that many people face.
4Community
The rare disease community is extremely active and provides invaluable support to people living with a rare condition.
Effective treatment, management and co-ordination of care, coupled with support from patient groups, can improve the lives of patients and their families. Different forms of support are available, even if a disease-modifying treatment is not yet available for a patient's condition.
Patient advocacy groups (PAGs), which can be either disease-specific or umbrella groups, provide information, resources and community support for patients and families. The graphic here shows just a few of the groups that exist, including SWAN UK, which supports families of children and young adults with undiagnosed rare genetic conditions known collectively as syndromes without a name (SWAN).
For professional resources and training, visit Medics for Rare Disease, a UK-based charity that champions greater awareness of rare conditions.
5Summary points
- Though rare diseases are individually rare, they are collectively common, affecting about 1-in-17 people at some point in their lives.
- There are more than 7,000 known rare diseases. About 80% are believed to be genomic.
- Though it is impossible to know about every rare disease, it is possible to know the patterns suggestive of one. 'Thinking rare' can save lives and may prevent unnecessary hardship.
- Understanding the experience of being rare, and signposting to relevant support groups, can be as important as clinical management.
- Patient advocacy groups can provide valuable information, resources and community support for both diagnosed and undiagnosed patients and families.
6Learn more
Do you want to discover more about the application of genomics in rare disease? Why not try one of our resources:
