A genetic disease is a disease affecting the genome, that is to say the genetic code that governs the functions of all our cells. These genetic diseases are generally linked to a mutation of a gene, in other words to an anomaly of DNA, which will result in the synthesis of an abnormal protein (in its function or in its structure). This abnormal protein, depending on its role in different tissues of the body, depending on its importance, will have very variable consequences from one genetic disease to another.
Many genetic diseases are considered rare diseases. A disease is rare when it affects a limited number of people, less than one person in 2,000 in Europe. Some, such as Progeria or GAPO syndrome, affect less than 100 people worldwide.
Rare diseases certainly number in the thousands. At present, we have counted 6 to 7,000 genetic diseases and new ones are described every week. While almost all genetic diseases are rare diseases, all rare diseases are not genetic: 80% of rare diseases are diseases genetics. There are very rare infectious diseases as well as autoimmune diseases. For many diseases, the cause remains unknown to this day. A genetic or viral disease may be rare in one region and frequent in another one. Leprosy is a rare infectious disease in France, but frequent in Central Africa. Thalassemia is a rare genetic anemia in northern Europe, while it is frequent around the Mediterranean. Rare diseases are serious, chronic, progressive diseases. Diseases rare prevent movement (Friedrich’s ataxia, myopathies), breathing (cystic fibrosis), to resist infections (severe combined immunodeficiency = DICS) or in the light of the sun (disease of the children of the moon = Xeroderma pigmentosum), to grow (achondroplasia, glass, syndrome) or make them grow more quickly (Sotos syndrome); they can cause mental retardation (syndrome of fragile X, galactosemia), cause aging (progeria). Other rare diseases beginning in childhood: amyotrophy infantile spinal, galactosemia, brittle bone disease, Tay-Sachs disease, Wilson, cystic fibrosis, Duchenne muscular dystrophy, neurofibromatosis, progeria, Sotos syndrome etc.
Other rare diseases beginning in adulthood: genetic hemochromatosis, Gardner syndrome. However, more than 50% of rare diseases appear in adulthood, such as Huntington’s chorea or Saint-Guy’s dance.
For most rare diseases there is no cure, but proper care can improve quality of life and extend lifespan. Due to a lack of sufficient scientific and medical knowledge, a large number of sick is not diagnosed. Their illness remains unknown. At best, these people are cared for on the basis of the expression of their symptoms. All patients and their families describe an obstacle course to be listened to, to be informed, and to be directed to the competent teams, when they exist, in order to make the correct diagnosis.