Monogenic diseases are what we call genetic syndromes, meaning that they result from a genetic mutation. According to the nature of the mutation and to the affected gene, various diseases can occur, which have different prevalence in a population.
Monogenic diseases are inherited to the next generation showing a wide range of symptoms and severity, depending on the disorder.
The inheritance pattern of a monogenic disorder defines if a person shows symptoms of the disease or if he is just considered carrier. In the latter case, the person carries the mutated gene and may inherit it to his children, despite that he does not show symptoms of the disease, himself. A carrier may know his condition, especially when family history occurs, or may be totally unaware of the fact.
The modern techniques of Molecular Biology allow the accurate diagnosis of monogenic diseases. Nowadays, it is possible to precisely define the kind of the particular mutation that causes the disorder. One of the most frequent and important monogenic diseases that can be tested are Thalassaemia, Cystic fibrosis, muscle dystrophies, achondroplasia, fragile X syndrome, deafness, etc. Moreover, a large number of other monogenic diseases can also be discovered, after molecular analysis, in respect to the medical history of each patient. Given that someone may be the first person in a family, showing a mutation related to a monogenic disease, there are cases in which finding the responsible gene is a result of thorough investigation. It is important for a couple to do the examinations for at least the most frequent diseases (thalassaemia, cystic fibrosis) during the prenatal testing, in order to exclude the case of having an affected child. In case that both partners are carriers of the same monogenic disorder, then it is suggested to accept genetic counseling in order to be informed and guided to the safest way of having healthy children.