Rare Diseases
Rare diseases are health conditions that each affect a small number of people, but together they touch millions. Information is often scattered and hard to understand, which can delay diagnosis and support. This page brings trustworthy, easy-to-read guidance into one place so that patients, families, and the public can find what they need quickly, and so that clinicians, researchers, students, startups, and investors can connect around real needs.
In the European Union and the United Kingdom, a disease is classified as rare if it affects fewer than 1 in 2,000 individuals. However, there is no globally agreed definition, and each country sets its own criteria for what constitutes a rare disease within its population. What is certain is that many rare conditions often go undiagnosed for years.
Rare diseases can manifest through a wide range of symptoms, many of which may seem unrelated at first glance. These conditions can arise at any stage of life, whether in childhood, adulthood, or both. Sometimes they impact only one part of the body, while in other cases, they affect multiple systems or organs. The symptoms and overall burden of rare diseases are as varied and complex as the disorders themselves.
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Global Prevelance & Definitions
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What are the examples of Rare Diseases?
For a detailed list of recognized rare conditions, you can consult the following resources:
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Orphanet Database for Rare Diseases and Orphan Drugs
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National Organization for Rare Disorders (NORD) Rare Disease Database
Rare diseases can generally be divided into genetic and non-genetic types. When a condition is not genetic, its cause is usually linked to environmental factors. These may include bacterial or viral infections, allergens, or exposure to harmful substances such as asbestos. In some cases, however, the underlying cause of a rare disease remains unknown.
Examples of Rare Diseases include:
Cystic Fibrosis (CF) is one of the more common rare genetic disorders, affecting the lungs and digestive system.
CF affects about 105,000 people worldwide, including ~11,000 in the UK.
Huntington’s Disease (HD) is a genetic condition that leads to progressive brain cell degeneration.
HD occurs in about 5 per 100,000 people, with similar rates in the U.S. and Europe.
Fibrodysplasia Ossificans Progressiva (FOP) is an extremely rare genetic disease where soft tissues gradually turn into bone.
In fact, only around 800–900 cases are known globally.
Fields’ Syndrome is one of the rarest known conditions in the world, causing muscle weakness and spasms, with fewer than five documented cases.