Very Rare Diseases

Rare diseases are often life-threatening or chronically restrictive diseases that require special treatment. Depending on the country or the federation, various criteria apply for classification as a rare disease.

For example, the relevant EU regulation, as a rare disease, defines a “life-threatening or chronic disability” that affects no more than five out of ten thousand people in the European Community. [1] Many rare diseases are caused by a genetic defect.


What is a rare disease?

“Rare diseases” are those disorders, of which only a comparatively small number of people are affected. In Europe, a disease is classified as rare if it affects at most one among 2,000 people. The ‘rare’ status can change over time or regionally. Thus thalassemia, a genetically determined form of blood poverty, is rare in Northern Europe, but often in the Mediterranean countries. There are also diseases which are frequent in their chief symptoms but rarely occur in special forms.

How many rare diseases are there?

There are thousands of rare diseases. Six to seven thousand rare diseases have already been found, and new rare diseases are regularly described in medical specialties. The number of existing rare diseases also depends on the specificity of the classification of rare entities/diseases. In medicine, a health disorder is defined with a circumscribed configuration of symptoms and a uniform treatment of a particular disease. Such a delineation depends on the acuteness of the analytical approach. The more differentiated our investigation, the more differences between individual cases of illness are recognized. This fact is reflected in the different classifications provided by Orphanet.


What are the characteristics of rare diseases?

Almost all genetic disorders are rare diseases, but not all rare diseases are genetic diseases. For example, there are e.g. Very rare infectious diseases, rare forms of autoimmune disorders or even rare cancer diseases. For most rare diseases, the causes are not yet explained.
Rare diseases are serious, often chronic and progressive diseases that are often life-threatening. In many rare diseases, the first symptoms may occur shortly after birth or early childhood (e.g., proximal spinal muscular atrophy, neurofibromatosis, osteogenesis imperfecta, chondrodysplasia, or Rett’s syndrome). In over 50% of the rare diseases, the disease manifests itself only in the adult age (e.g., Huntington’s disease, Crohn’s disease, Charcot-Marie-Tooth disease, amyotrophic lateral sclerosis or Kaposi’s sarcoma).

What are medical and social consequences the result of rare diseases?


The medical and scientific knowledge of rare diseases is far from sufficient. The topic of “rare diseases” has long been neglected by doctors, politicians, and scientists, so that until recently, neither suitable health policy nor scientific measures existed. For most rare diseases, there is no effective therapy, but appropriate care measures can improve the quality of life and also increase life expectancy. Some impressive progress has been made in the treatment of certain diseases, which should motivate us to intensify research efforts and to further strengthen social solidarity.
Patients with rare diseases are often confronted with similar problems. Difficulties arise, in particular, with regard to the diagnosis, the availability of relevant information and the transfer of suitable experts. Equally important is access to qualified specialist institutions, general social and medical support, effective collaboration between hospitals and general practitioners, professional and social integration, or the maintenance of self-employment.

Those affected are often faced with psychological, social, economic or cultural problems. Difficulties of this kind could be prevented by rational regulations. Many patients are not diagnosed because a rare disease is often not recognized due to a lack of sufficient scientific and medical knowledge. It is precisely this group of patients who are exposed to the greatest suffering since they are denied access to appropriate support.


Will the diagnosis and treatment of rare diseases improve?


In view of a basic understanding of the rare diseases, science can provide some answers. Today, hundreds of rare diseases can be detected by a simple biological test. For some of the diseases, the knowledge about the natural course of the disease could be expanded by the establishment of registers.

The formation of networks promotes the exchange of knowledge and leads to an improvement in research efficiency. The overall perspective has improved, as in many European countries new foundations for combating rare diseases have been created through changes in legislation and national efforts.

What measures in Europe deal with the rare diseases?

A presentation of the European approach in the field of rare diseases and orphan drugs can be found on the European Commission’s website:
A description of the current national initiatives in Europe, as well as an overview of the incentives of the European Commission and the European Community, are available on the website of the European Committee of Experts on Rare Diseases:

How do I get information about a particular illness?

Orphanet includes a list of rare diseases and provides information on over 6000 of these diseases. The database also provides information on specialized services offered by the countries involved in the Orphanet consortium.