The term rare disease has different definitions in different parts of the world. For example, in Europe, it is defined as diseases that affect less than 1 in 2000 citizens (Orphan Drug Regulation 141/2000). In the United States, rare disease is defined as a condition affecting fewer than 200,000 patients. In Japan, it is used for diseases that affect less than one in 2500 individuals. Neglected diseases affect about 1/6th of the world’s population, the World Health Organization (WHO) estimates that more than 1 billion people suffer from one or more neglected diseases. The National Institutes of Health estimates there are more than 6,000 rare diseases affecting 25 million Americans. Diseases lacking substantial therapeutic development activity are considered neglected diseases, which create an enormous public health burden, as one of these diseases alone can affect over 200 million patients.
