22 November 2021
Rare diseases are diseases which affect a small number of people compared to the general population and whose rarity raises specific issues. 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. For example, thalassemia (an anaemia of genetic origin) is rare in Northern Europe, but 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.
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.
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 of many rare diseases remains unknown.
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.
The field of rare diseases suffers from a deficit of medical and scientific knowledge. For a long time, doctors, researchers and policy makers were unaware of rare diseases and until very recently there was no real research or public health policy concerning issues related to the field. There is no cure for most rare diseases, but the appropriate treatment and medical care can improve the quality of life of those affected and extend their life expectancy. Impressive progress has already been made for certain diseases, which shows that we must not give up the fight, but on the contrary, continue and step up efforts in the fields of research and social solidarity.
Those affected by these diseases all face similar difficulties in their quest for a diagnosis, relevant information and proper direction towards qualified professionals. Specific issues are equally raised regarding access to quality health care, overall social and medical support, effective liaison between hospitals and general practices, as well as professional and social integration and independence.
Those affected by rare diseases are also more psychologically, socially, economically and culturally vulnerable. These difficulties could be overcome by appropriate policies. Due to the lack of sufficient scientific and medical knowledge, many patients are not diagnosed and their disease remains unidentified. These are the people who suffer the most from difficulties in receiving appropriate support.
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.
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.