What is a rare disease?

A rare disease is defined by the European Union as one that affects less than 5 in 10,000 of the general population. There are between 6,000 and 8,000 known rare diseases and around five new rare diseases are described in medical literature each week.

1 in 17 people, or 7% of the population, will be affected by a rare disease at some point in their lives. This equates to approximately 3.5 million people in the UK and 30 million people across Europe.

In the UK, a single rare disease may affect up to about 30,000 people. The vast majority of rare diseases will affect far fewer than this – some will affect only a handful, or even a single person in the whole of the UK.

80% of rare diseases have a genetic component. Often rare diseases are chronic and life-threatening. Rare diseases can be single gene, multifactorial, chromosomal or non-genetic.

75% of rare diseases affect children. Rare diseases include rare cancers such as childhood cancers and some other well known conditions, such as cystic fibrosis and Huntington’s disease.

For further information on specific rare diseases please see Orphanet, the portal for rare diseases and orphan drugs, or check out the supporters of the Rare Disease UK (RDUK) campaign for relevant patient organisations.

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