Rare diseases are diseases which affect a small number of people compared to the general population and specific issues are raised in relation to their rarity. Up to now, around 7000 rare diseases have been discovered and new diseases are regularly described in medical literature. Rare diseases are serious, often chronic and progressive, diseases. There are many different causes of rare diseases. The majority are thought to be genetic, directly caused by changes in genes or chromosomes. In some cases, genetic changes that cause disease are passed from one generation to the next. In other cases, they occur randomly in a person who is the first in a family to be diagnosed.