In the U.S., orphan diseases are conditions impacting fewer than 200,000 people. There are more than 7,000 of these rare conditions affecting an estimated 30 million Americans — and more than 300 million people globally — and new diseases continue to be discovered. Most of them are inherited conditions caused by gene mutations, but some can be caused by environmental factors. These diseases may be serious and even life-threatening, and about half of them affect children.
Before the Orphan Drug Act was passed in 1983, not much research was done into treatments for rare diseases. But that law created financial incentives for pharmaceutical manufacturers, and since then, hundreds of orphan drugs have been developed. As of early 2020, the FDA had approved therapies for more than 800 rare diseases.