Rare diseases are diseases that are generally caused by genetic reasons and that are found in relatively smaller number of people in the society.
Mostly thought to be genetically transmitted, rare diseases can have chronic and permanent heavy results on the individual if they are not diagnosed and treated. Since the probability of discovering the rare diseases in the first assay is low, it can be said that the importance of these diseases need to be even higher.
It is estimated that there are about 7.000 rare diseases in the World and although these diseases are called “rare”, they are thought to be affecting 5 to 6 percent of the world population, in other words nearly 350 million people. Since most of the rare occurring diseases are not followed up, it is hard to certainly state the number of rare diseases and how many people are affected by them.
Diseases that affect 1 in every 2.000 people are accepted as rare disease by European Union. This ratio is regarded as diseases that affect 1 in every 200.000 people in The United States of America.
It is thought that the types of rare diseases in the whole World change between 5.000 and 8.000.