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.

Errant Diagnosis

A lot of rare diseases are affected by the problem of an errant diagnosis: wandering from one doctor to another, trying ineffective treatments that follow incorrect diagnoses and sometimes never even receiving a diagnosis. 

This difficulty to identify diseases is an additional source of psychological suffering for the patient and for those close to them.

Rare diseases are difficult to diagnose because:

  • the symptoms are varied, complex and involve multiple medical specialties 
  • not all doctors are aware of all rare diseases 
  • some rare diseases have not even been described yet.

Genetic tests

80% of rare diseases have a genetic origin. Genetic tests are available for approximately 50% of rare diseases.

A genetic test can be carried out:

  • if someone is suffering from symptoms that resemble those of a rare genetic disease 
  • if a genetic disease has clearly been identified within the family 
  • within the framework of a pre-implantation diagnosis (detection of a known genetic or chromosomal abnormality in the embryos conceived following in-vitro fertilization)
  • during pregnancy with prenatal screening (combined or triple test for trisomies 13, 18 and 21), with a non-invasive prenatal test (NIPT) or another genetic test
  • at birth (neonatal screening) 

To find out more about genetic tests:



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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