A disease or disorder is defined as rare in Europe when it affects fewer than 1 in 2000.
A disease or disorder is defined as rare in the USA when it affects fewer than 200,000 Americans at any given time.
One rare disease may affect only a handful of patients in the EU (European Union), and another may touch as many as 245,000. In the EU, as many as 30 million people may be affected by one of over 6000 existing rare diseases.
80% of rare diseases have identified genetic origins whilst others are the result of infections (bacterial or viral), allergies and environmental causes, or are degenerative and proliferative.
50% of rare diseases affect children.