Rare Diseases

Updated: Jul 24

What is a rare disease?

#Rare diseases are diseases which affect a small number of people compared to the general population and specific issues are raised in relation to their rarity. In Europe, a disease is considered to be rare when it affects 1 person per 2000. A disease can be rare in one region, but common in another.

This is the case of thalassemia, an anaemia of genetic origin, which is rare in Northern Europe, but it is frequent in the Mediterranean region. 'Periodic disease' is rare in France, but common in Armenia. There are also many common diseases whose variants are rare.

How many rare diseases are there?

There are thousands of rare diseases. To date, six to seven thousand rare diseases have been discovered and new diseases are regularly described in medical literature. The number of rare diseases also depends on the degree of specificity used when classifying the different entities/disorders.

Until now, in the field of medicine, a disease is defined as an alteration of the state of health, presenting as a unique pattern of symptoms with a single treatment. Whether a pattern is considered unique depends entirely on the level of definition of our analysis. The more accurate our analysis, the more we notice certain nuances. This complexity is reflected in the various classifications provided by Orphanet.

What are the origins and characteristics of rare diseases?

While nearly all genetic diseases are rare diseases, not all rare diseases are genetic diseases. There are also very rare forms of infectious diseases, such as auto-immune diseases and rare cancers. To date, the cause remains unknown for many rare diseases.

Rare diseases are serious, often chronic and progressive, diseases. For many rare diseases, signs may be observed at birth or in childhood, as is the case of proximal spinal muscular atrophy, neurofibromatosis, osteogenesis imperfecta, chondrodysplasia or Rett syndrome. However, over 50% of rare diseases appear during adulthood, such as Huntington diseases, Crohn disease, Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis, Kaposi's sarcoma or thyroid cancer.

What progress is foreseen in the diagnosis and treatment of rare diseases?

For all rare diseases, science can provide some answers. Hundreds of rare diseases can now be diagnosed through a biological sample test. Knowledge of the natural history of these diseases is improved by the creation of registries. Researchers are increasingly working through networks in order to share the results of their research and to advance more efficiently. New hopes arise with the perspectives offered by European and national policies in many European countries in the field of rare diseases.

How can I obtain information about a specific disease?

Orphanet provides an inventory of rare diseases and related information for over 6000 of these diseases, as well as a directory of expert resources in the countries of the consortium.

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