Around 3.5 million people in the UK are living with a rare disease. Although each condition affects only a small number of people, there are thousands of rare diseases worldwide, many of which have limited research and no approved treatment. Continued investment in rare disease research and clinical trials is essential to improve diagnosis, develop new therapies and support those living with these conditions.
As specialists in rare disease clinical trials, we’ve created this guide to explain what rare diseases are, the challenges they present, and the vital role research plays in advancing treatment.
In this guide, we’ll explore:
- Rare diseases vs orphan diseases
- Examples of rare diseases
- What causes rare diseases?
- How are rare diseases diagnosed?
- Why are rare diseases called ‘zebras’?
- The challenges of living with a rare disease
- The role of clinical trials
- Frequently asked questions
What is a rare disease?
A rare disease is a condition that affects a small proportion of the population. In the UK and Europe, a disease is generally considered rare if it affects fewer than 1 in 2,000 people. While each condition is uncommon individually, there are over 7,000 recognised rare diseases worldwide, collectively affecting millions of people and often requiring specialised diagnosis, treatment and research.
Key facts
- Over 7,000 rare diseases have been identified worldwide.
- Over 300 million people globally are living with a rare disease.
- Approximately 80% of rare diseases are genetic in origin.
- Many rare diseases have no approved treatment, highlighting the need for continued clinical research and drug development.
What is an orphan disease?
The terms rare disease and orphan disease are often used interchangeably, but they have different meanings. A rare disease refers to a condition that affects a small number of people, whereas an orphan disease is a condition for which there is limited financial incentive to develop new treatments.
Because patient populations are small, pharmaceutical companies may struggle to recover the costs of developing new medicines. To encourage research, legislation such as the Orphan Drug Act introduced incentives to support the development of orphan drugs, helping to accelerate research and improve access to treatments for people living with rare diseases.
Diagnosing rare diseases
Diagnosing a rare disease can be challenging. Because many rare conditions affect so few people, symptoms are often unfamiliar and may overlap with those of more common illnesses. This can make it difficult for healthcare professionals to identify the correct condition, particularly when there is limited research or awareness.
Reporting symptoms
Providing a complete picture of your symptoms is an important part of the diagnostic process. Even symptoms that seem unrelated or insignificant can help healthcare professionals identify a rare condition and determine whether further investigations are needed.
Misdiagnosis
Many rare diseases share symptoms with more common conditions, which can lead to delays or misdiagnosis. Healthcare professionals may need to rule out several possible causes before reaching an accurate diagnosis. Although this process can be frustrating, it is often a necessary step in ensuring patients receive the most appropriate care and treatment.
Some rare diseases closely mimic the symptoms of more common conditions, meaning patients may initially receive an incorrect diagnosis. Healthcare professionals often need to rule out several possible conditions before identifying the underlying cause. Although this process can be frustrating, it is an important step towards ensuring patients receive the most appropriate care.
Rare diseases and zebras
If you’ve researched rare diseases, you may have come across the term “zebra”. The nickname originates from a well-known saying taught in medicine:
“When you hear hoofbeats, think horses, not zebras.”
The phrase encourages healthcare professionals to consider the most common diagnosis first. However, for people living with rare diseases, this approach can sometimes delay diagnosis because uncommon conditions may be overlooked.
As a result, the zebra has become an internationally recognised symbol of the rare disease community. It represents the importance of considering less common conditions, raising awareness of rare diseases, and improving access to timely diagnosis and treatment.
What causes rare diseases?
There is no single cause of rare diseases. With more than 7,000 recognised rare diseases, the underlying causes vary depending on the condition. However, most rare diseases are caused by genetic changes that are either inherited from parents or occur spontaneously before birth.
Other rare diseases may develop as a result of infections, environmental factors or changes within the body’s cells. In some cases, the exact cause remains unknown, highlighting the need for continued research and clinical studies.
Common causes of rare diseases include:
- Genetic mutations – Changes in a person’s DNA are responsible for the majority of rare diseases.
- Inherited conditions – Some rare diseases are passed down through families, even if parents do not show symptoms themselves.
- Chromosomal abnormalities – Missing, duplicated or altered chromosomes can lead to certain rare conditions.
- Infections – Although less common, some rare diseases are caused by viruses, bacteria or other infectious agents.
- Environmental factors – In some cases, exposure to certain environmental influences may contribute to the development of a rare disease.
Understanding what causes rare diseases is an important step towards improving diagnosis and developing new treatments. Continued investment in research and clinical trials is helping scientists better understand these conditions and identify new therapeutic approaches.
The role of clinical trials
Clinical trials are essential to improving the diagnosis and treatment of rare diseases. As many rare conditions have no approved therapies, research is critical to developing new medicines and advancing our understanding of these complex conditions.
Rare disease clinical trials can be particularly challenging due to small patient populations, limited existing research and the need for specialist study designs. However, every trial contributes valuable evidence that can help bring new treatments to patients.
At Simbec-Orion, we specialise in designing and delivering rare disease clinical trials, helping to accelerate the development of innovative therapies for rare and orphan diseases.
When is Rare Disease Day?
Rare Disease Day takes place every year on the last day of February. It is a global awareness campaign that aims to improve understanding of rare diseases, promote earlier diagnosis and encourage investment in research and treatment.
The day also highlights the challenges faced by people living with rare diseases, including limited access to specialist care, delays in diagnosis and the need for greater research into new therapies. By raising awareness, Rare Disease Day helps drive support for patients, families and the organisations working to improve outcomes.
Rare diseases: Final thoughts
At Simbec-Orion, we are passionate about helping to advance the treatment of rare diseases. If you’d like to discover more about studies into rare disease, you can browse a selection of clinical development case studies on our website.
We also have a dedicated whitepaper on this topic: Putting The Patient First: The Challenges and Opportunities to Improve Rare-Disease Therapy Development. If you’d like to discover more about the challenges faced by those researching rare diseases and what you can do to help, this whitepaper is free to download. If you would also like to get involved in Rare Disease Day, you can learn more about the events which take place worldwide on the official Rare Disease Day website. You can even list your own if you would like to take part and fundraise for those affected by rare diseases and conditions.
Contact Simbec-Orion today
Get in touch with our team here at Simbec-Orion for more information on rare disease clinical trials. You can also learn more about how Simbec-Orion uses biomarker clinical trial design to drive rare respiratory disease results.
Frequently asked questions on rare diseases
How many rare diseases are there?
There are more than 7,000 recognised rare diseases, collectively affecting around 300 million people worldwide. Although each condition is uncommon, rare diseases affect millions of people globally.
What are some examples of rare diseases?
Examples of rare diseases include Cystic Fibrosis, Amyotrophic Lateral Sclerosis (ALS), Ehlers-Danlos syndrome, Prader-Willi syndrome and Congenital Insensitivity to Pain with Anhidrosis (CIPA). Rare diseases vary widely in their symptoms, severity and the parts of the body they affect.
Are most rare diseases genetic?
Around 72% of rare diseases are genetic, meaning they are caused by changes in DNA that may be inherited or occur spontaneously. Other rare diseases may result from infections, environmental factors or unknown causes.
Can rare diseases be treated?
While treatments are available for some rare diseases, many still have no approved therapy. Clinical trials play a vital role in developing new medicines and improving care for people living with rare diseases.
Why are clinical trials important for rare diseases?
Clinical trials help researchers better understand rare diseases and evaluate potential new treatments. Despite the challenges of studying small patient populations, these trials are essential for improving outcomes and advancing medical research.