are diseases (sometimes they are called orphan diseases) are such illnesses that affect only the smallest part of the human population. To stimulate the research of these diseases and find the effective treatment a financial support from the government is often required.
Many of the orphan diseases are genetic ones and torture the person during the whole life even in the cases of a long latent period when the symptoms remain implicit for a long period of time. Many rare diseases tent to appear in an early childhood and nearly 30 % of children suffering from them don’t reach the age of 5 years old.
There is no single level of a particular disease dissemination to provide the reasons for considering it to be a rare or a common one. A disease may supposed to be a rare one in the one country or a detached community and widespread in another.