What is the definition of a rare disease?

A rare disease, also known as an "orphan disease," refers to diseases with relatively low prevalence rates. The definition of rare diseases varies across different countries and regions, and these differences are typically based on prevalence rates, the number of patients, or other relevant factors.

·In the United States, the Orphan Drug Act enacted in 1983 provided a dual definition for rare diseases: diseases affecting fewer than 200,000 people in the U.S.; or diseases affecting more than 200,000 people, but for which the development and marketing costs of a drug are not expected to be recovered.

·In the European Union, a rare disease is defined as having a prevalence of less than 1 in 2,000 people.

·In China, the "China Rare Disease Definition Research Report 2021" proposed defining rare diseases as diseases with a neonatal incidence rate of less than 1 in 10,000, a prevalence rate of less than 1 in 10,000, or a total number of patients less than 140,000.

·In Japan, diseases affecting fewer than 50,000 people are defined as rare diseases.

Rare diseases often involve multiple systems and organs, and their clinical course is typically chronic, progressive, and debilitating, sometimes leading to disability or life-threatening conditions. Due to the small number of patients for each rare disease and the scarcity of information, the development of drugs for rare diseases is extremely challenging, and these drugs are sometimes referred to as "orphan drugs."

To address the challenges posed by rare diseases, some countries or regions have established relevant policies and regulations to promote the diagnosis, treatment, and research of rare diseases, while ensuring that patients can access necessary medical and social security support.