A disease or disorder is defined as rare when it affects less than 5 in 10000. Such a low prevalence of the disease makes it very difficult to get diagnosis of the disease. Until now between five to eight thousand rare diseases have been identified in the world. A rare disease is of low prevalence ranging between 1 in 1000 to 1 in 200000. Number of people affected by rare diseases is very low and limited. For example total number of people affected by rare diseases in France is less than the total number of people affected by cancer in this country. It is worth mentioning that major part of the rare diseases (around 80%) are genetically caused. People who are affected by one of the rare diseases often suffer from the relevant complications until the end of their lives; the complications that may develop at certain level of the progress of the disease. In some cases of congenital rare diseases the mortality rate in the patients with 5 years old stands at 30% of total number of the affected individuals.
What is a rare disease?
Rare diseases are also sometimes called orphan diseases because there is no effective treatment for them and all prescriptions and therapeutic methods introduced for them mean just to limit and contain their symptoms and complications.
It is to be mentioned that there are a number of more prevalent diseases like dementia or Alzheimer’s that are included in the list of orphan diseases while they are not considered as rare ones.