What is a Rare Disease ?

Rare diseases are diseases that affect a small number of people compared to the general population.

Over 300 million persons worldwide live with a rare disease. 

Rare diseases currently affect 3.5% – 5.9% of the worldwide population


There are over 6 000 different identified rare diseases, and more being discovered.

Whilst certain rare conditions of genetic and infectious origin may be rare in global terms, they may be relatively common in some regions.

Most rare diseases are characterised by a paucity of sufficient scientific and medical knowledge, and persons living with the same rare disease are often geographically scattered.


72% of rare diseases have genetic origins.


70% of rare genetic diseases start in childhood.

Not all rare conditions are of genetic origin. Other rare diseases include rare infections (bacterial or viral) and rare cancers.

A significant number of rare diseases also appear in adults.


Rare diseases are often chronic, heavily disabling and life-threatening. They all have an impact on multiple aspects of the lives of persons living with a rare disease (PLWRD) and their families .

Despite their great overall number, the low prevalence of each rare disease results in a scarcity of expertise and scientific knowledge about rare diseases, limited access to diagnosis and holistic care, and a general lack of public awareness of rare diseases.

Consequently, rare diseases are associated with a substantial health, economic and social burden that is borne by patients, caregivers, healthcare systems and societies at large.


PLWRD around the world confront common health, social and economic challenges.

RDI represents the global community of over 300 million PLWRD.

Together, we advocate for rare diseases as an international policy priority, raise public awareness, promote global collaborations, and are working to help strengthen health systems to better care for PLWRD everywhere.


Key References on Rare Diseases