Rare Diseases General

The term “rare diseases” is used to refer to diseases that occur in a relatively small number of people. They often involve specific problems because of the fact that they are rare.

In Europe, a disease is classified as rare if it occurs in fewer than 1 in 2000 people. A disease can be rare in one region, but common in another. There are also common diseases that have rare variants.

You can find general information about rare diseases below. For specific information about the different rare diseases, visit Orphanet

How many rare diseases are there?
There are thousands of known rare diseases. Around 7000 rare diseases have been discovered to date and new diseases are still described in the medical literature on a regular basis.

What are the causes and characteristics of rare diseases?
Many rare diseases are of genetic origin. Although almost all genetic diseases are rare, not all rare diseases have a genetic origin. For example, there are also very rare infectious diseases, rare autoimmune diseases and rare forms of cancer. The cause of many rare diseases still remains unknown.
Rare diseases are serious, often chronic and progressive conditions. For many rare diseases, symptoms are already noticeable at birth or become evident in childhood. However, more than 50% of rare diseases do not become apparent until adulthood.

What are the medical and social consequences of the ‘rarity’ of these diseases?
The field of rare diseases suffers from a shortage of medical and scientific knowledge. For a long time, physicians, researchers and policymakers were not aware of rare diseases and until recently there was no real research or policy in the field of these diseases. The majority of rare diseases cannot be cured, however the right treatment and medical care can lead to an improvement in quality of life and an increase in life expectancy. Impressive progress has already been made in the case of certain diseases.
Those affected by rare diseases often encounter the same problems in their search for a diagnosis, relevant information and an appropriate referral to qualified individuals. These problems also apply to access to high quality health care, social and medical support, effective cooperation between GPs and hospitals, and social and work-related integration and independence. People who suffer from a rare disease are also more vulnerable from a psychological, social, economic and cultural point of view. These problems can be overcome through appropriate policy. The lack of adequate scientific and medical knowledge means that many patients do not receive a diagnosis: their diseases remain unknown. These are the people who experience the most difficulties in obtaining appropriate support.

The Belgian Plan for Rare Diseases (in Dutch or in French) formulates various action points with the aim of finding a solution to these problems.

What progress is expected in the diagnosis and treatment of rare diseases?
For all rare diseases, science can provide a number of answers. Hundreds of rare diseases can now be diagnosed simply by means of a biological test. For certain rare diseases, knowledge of the course of the disease can be improved by setting up databases of patient data. More and more researchers are joining networks in order to share the results of their research with others and thereby make more progress. New hope is also offered by the prospect of appropriate policy in the field of rare diseases at European level and, for many European countries including Belgium, also at national level.

What is Europe's policy on rare diseases?
A description of European policy in relation to rare diseases can be found on the website of the European Commission.
A description of the national initiatives in Europe and the surrounding countries and the guidelines issued by the European Commission and the European Union can be found in the 2014 EUCERD report.