Recessive diseases are those genetic diseases in which both copies of the same gene are damaged. That is, a person who only has one mutated copy will be a “carrier” of the disease, but will not develop the disease and, therefore, will not have any symptoms. However, a person who carries two damaged copies will develop the symptoms of the disease. Therefore, many of these diseases can be transmitted from parents to children without them having any suspicion of it. If it coincides that both the mother and the father are carriers of the same disease, approximately 25% of their children will suffer from the disease.
Recessive diseases are known as rare diseases, since they are rare. Although this category assumes that the disease affects 1 in 2,000 people, there are more than 7,000 rare diseases, so the combined incidence of all of them is high.