What is a rare disease ?
The so-called 'rare diseases' are diseases that affect a small number of people compared to the general population. In Europe, a disease is considered as rare when it affects 1 person per 2,000. However, this status may vary with time and also depends upon the area considered. For years, AIDS was an extremely rare disease, later it was rare, and now it is a more and more frequent disease in certain populations. A genetic or viral disease can be rare in one region, while frequent in another region. Leprosy is a rare disease in France, but common in central Africa. Thalassemia, which is an anaemia of genetic origin, is rare in Northern Europe, whereas it is frequent in the Mediterranean region. 'Periodic disease' is rare in France, whereas it is common in Armenia. There are also many 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 found and approximately five new diseases are described every week in the medical literature. This number also depends upon the accuracy of the definition. Whether a single pattern is considered unique depends on the state of our knowledge, on the accuracy of clinical and investigative analysis and on the way we choose to classify diseases in general. Certain related diseases can be considered as a unique entity (they are lumped together) or subdivided and classified as separate disorders (they are split). This complexity is reflected in the various classifications of rare diseases which are provided by Orphanet.
What is the origin of rare diseases ?
While most genetic diseases are rare diseases, all rare diseases are not caused by genetic defects. There are very rare infectious diseases for instance, as well as auto-immune diseases and very rare poisonings. To date, the cause remains unknown for most rare diseases.
What are the characteristics of rare disease ?
Rare diseases are serious chronic diseases, and are often life-threatening. For many rare diseases, signs may be observed at birth or in childhood, as in proximal spinal muscular atrophy, neurofibromatosis, osteogenesis imperfecta, chondrodysplasia or Rett syndrome. However, more than 50% of rare diseases may only appear during adulthood, such as Huntington disease, Crohn disease, Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis, Kaposi’s sarcoma or thyroid cancer. Scientific and medical knowledge on rare diseases is lacking and remains to be improved. Neglected for a long time by physicians, scientists and politicians, there were no adequate political and scientific research programmes in the field of rare diseases until a few years ago. There is no efficient treatment for most rare diseases, but suitable care can improve the quality of life and increase life expectancy. Spectacular progress has been achieved for some diseases indicating that it is not time to give up, but rather to pursue and to intensify research efforts and social solidarity.
What are the medical and social consequences for rare diseases ?
Patients face similar difficulties in their quest for a diagnosis, relevant information and proper direction towards qualified professionals. Many rare diseases are associated with sensory, motor or mental deficits and, sometimes, physical stigmata. People affected by rare diseases are often psychologically, socially, economically and culturally vulnerable. These difficulties may be overcome by proper regulation. Due to the lack of sufficient scientific and medical knowledge, many patients are not diagnosed. Their diseases remain unidentified. These people are the ones who suffer the most.
Will diagnosis and treatment of rare diseases improve ?
For all rare diseases, major hopes and significant changes should ensue from scientific progress, especially from the human genome programme. Hundreds of these diseases can now be targeted and diagnosed through biological sample analysis. Knowledge of the natural history of rare diseases is improved by the setting up of registers for some of them. Scientists are increasingly networking and sharing the results of their research to work more efficiently. New hopes arise from the implementation of orphan drug regulations. Support for this research effort varies considerably from one country to another, with few nations currently having political programmes targeted at rare diseases research.
How can I obtain information about a specific disease ?
Orphanet is a database of rare diseases which is freely accessible. It contains information about more than 5,000 diseases.
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