ABSTRACT
In the United States, rare or orphan disease is defined as a condition affecting less than 200,000 persons, which is approximately 63 per 100,000 persons. In Europe, a disorder is defined as rare when it affects fewer than 1 in 2000 (fewer than 50 per 100,000 persons). Because there are more than 6,000 rare diseases, it is estimated that 8% of the general population are affected by these disorders, many of whom remain undiagnosed.
