A rare disease, also referred to as an orphan disease, is any disease that affects a small percentage of the population. Most rare diseases are genetic, and are present throughout a person's entire life, even if symptoms do not immediately appear. In Europe a disease or disorder is defined as rare when it affects less than 1 in 2,000 people. In the United States, a rare disease is defined as a condition that affects fewer than 200,000 people in the US. In 2018, the Chinese government announced the first version of Rare Disease Catalogue which included 121 diseases such as Huntington Disease, Phenylketouria, Spinal Muscular Atrophy, etc.