A<unk>  is any<unk>  that affects a small percentage of the population. In some parts of the world, an orphan<unk>  is a<unk>  whose rarity means there is a lack of a market large enough to gain support and resources for discovering treatments for it, except by the government granting economically advantageous conditions to creating and selling such treatments. Orphan drugs are ones so created or sold. Most<unk> s are genetic and thus are present throughout the person's entire life, even if symptoms do not immediately appear. Many<unk> s appear early in life, and about 30% of children with<unk> s will die before reaching their fifth birthday. With only four diagnosed patients in 27 years, ribose-5-phosphate isomerase deficiency is considered the<unk> st known genetic<unk> . No single cut-off number has been agreed upon for which a<unk>  is considered<unk> . A<unk>  may be considered<unk>  in one part of the world, or in a particular group of people, but be common in another. The US organisation Global Genes has estimated that more than 300 million people worldwide are living with one of the approximately 7,000<unk> s they define as "rare" in the United States.
Rare disease
Progressive disease
Chronic condition
Contagious disease
Biphasic disease
Heterogeneous condition
Precancerous condition
Genetic heterogeneity