High-risk groups

Although some diseases are rare, the number of people suffering from them is significant. There are between 6,000 and 8,000 rare diseases affecting a total of 6 to 8% of Belgian people.

Risk factors

Everyone is susceptible to having a rare disease but certain factors can increase the risk:

  • consanguinity
  • belonging to certain ethnic groups (Tay-Sachs disease, sickle-cell anaemia, etc.)
  • risks from travelling abroad (hence the need for vaccination and other measures of prevention)
  • environmental exposure (for example to asbestos).

Rare genetic diseases

80% of rare diseases are of genetic origin: they are caused by an anomaly in a gene (for example cystic fibrosis) or a chromosome (for example trisomies). 

People who come from a family with a genetic deficiency have an increased risk of having the same genetic deficiency.

Genetic diseases can be hereditary but that is not necessarily the case.  

Please note! Genetics is only one piece of the puzzle. Environmental factors, such as diet, smoking or exposure to chemical products can also play a role in rare diseases. These factors can be the direct cause of a rare disease or interact with genetic factors and have an effect on the severity of the disease. 

DID YOU KNOW? 50% of rare diseases are evident in infancy and 30% of people affected by a rare disease die before the age of 5.


Sciensano is responsible for processing the data from the Central Registry of Rare Diseases, which aims to centralise certain data on all Belgian patients affected by a rare disease.

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