Current Science

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A large number of diseases have been grouped together as 'rare diseases', because we do not know much about them. There is no consensus on the definition of a rare disease. This is because, obtaining reliable statistical estimates of the frequency of occurrence of a rare event, such as prevalence of a rare disease, requires an inordinately large sample size, collection of which costs prohibitively large amount of money. Recognizing this limitation and the somewhat arbitrary nature of definition of a rare disease, we can use the definition adopted by the World Health Organization: A rare disease is a disease whose prevalence in a given country or a region is lower than 1 in 10,000 persons.
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