In the United States, a rare disease is defined as a condition that affects fewer than 200,000 people. This definition was created by Congress in the Orphan Drug Act of 1983. There are over 7,000 rare diseases. 1 in 10 have a rare disease. Which means the total number of Americans living with a rare disease is estimated to be ~30 million and in Alabama ~500,000. 95% of rare diseases do not have an FDA approved therapy.

In the European Union, a disease is defined as rare when it affects fewer than 1 in 2,000 people.