An orphan disease is characterized by affecting how many people in the U.S.?

An orphan disease is defined as a condition that affects a relatively small number of individuals, specifically fewer than 200,000 people in the United States. This definition is important because it influences research funding, drug development, and the regulatory environment for treatments specific to those conditions. The designation encourages pharmaceutical companies to develop therapies for these diseases, as they might not be financially viable otherwise due to the small patient population.

The other options present larger population thresholds which do not align with the established definition of orphan diseases. By focusing on the threshold of 200,000, the correct answer reflects the specific parameters set forth by regulatory agencies for identifying orphan diseases.