Rare disease« Back to Glossary Index
A rare disease, also referred to as an orphan disease, is any disease that affects a small percentage of the population. Rare disease are commonly defined as life-threatening or chronically debilitating diseases which are of such low prevalence (fewer than 1 in 2,000 people) that special combined efforts are needed to address them. Diseases that are statistically rare, but not also life-threatening, chronically debilitating, or inadequately treated, are excluded from this definition. A disease may be considered rare in one part of the world, or in a particular group of people, but still be common in another.