Are all genetic diseases inherited or transmissible?

All cells that constitute our organism contain the necessary machinery, known as DNA or genetic material, to carry out the functions and maintenance of our body. Its distribution in genes and regulatory elements allows the production of proteins, which are the biomolecules in charge of carrying out most of the functions mentioned above.

Any alteration in the DNA can cause the altered expression of one or more genes, resulting in a protein that does not function correctly or the absence of the protein. The occurrence of these variations can take place in any cell of the organism, thereby originating a particular genetic disease. These alterations can be due to spontaneous changes (errors during the generation of new cells) or induced by external agents that cause the DNA to suffer these alterations. In addition, an individual can inherit a genetic variation from one or both parents or it can simply occur throughout their life.

We can see that there are different types of cells and that each one is specialized in a certain function. There are two different large cell groups: somatic cells and germ cells. Depending on the cell type where a variation occurs, it will have different consequences both clinically and in terms of inheritance of a disease.

Somatic cells are the majority cells since these are all the cells of the body except for germ cells and, therefore, are responsible for most of the processes carried out in the body (breathing, digestion, sweating, bone formation, etc.). These cells renew themselves throughout an individual’s life. Therefore, when a variant originates at the somatic level, this cell will give rise to a population of identical cells known as clones. These somatic variations can be harmless or pathogenic. If they are pathogenic (disease-causing) and occur in genes that give rise to an uncontrolled growth of these somatic cells that will eventually generate a cell mass called a cancerous tumor. Because they are cells that are not part of the individual’s reproductive cells, these variants will not be passed on to the next generation. These are genetic diseases, but not transmissible.

Germ cells, on the other hand, have a very specific and fundamental function in the reproduction of our species, as they are created by primordial germ cells that act as precursors of germ cells: oocytes and sperm cells. When an individual carries a pathogenic variant in all the cells of his body (somatic and primordial germ cells), this variant can be transmitted to the offspring. Depending on the gene affected, these variants can cause recessive diseases such as cystic fibrosis if the offspring inherit a disease-related disorder from both of their parents (these are asymptomatic) or dominant diseases such as achondroplasia, if the offspring inherit a disease-related disorder from one of their parents (also affected by the disease). In this case, these are transmissible genetic diseases.

In exceptional cases, an individual may not carry a pathogenic variant in his cells, but during the process of oocyte or sperm formation, a de novo mutation may occur, which will result in offspring carrying the new pathogenic variant in all their cells. In this case, although the offspring have not inherited the disease, it is a transmissible disease that can affect their future offspring (third generation of the family).

Both somatic variations in tumors and variations present in all the cells of the individual can be detected by specific genetic tests depending on the type of variant to be identified. It is therefore necessary to consult a specialist to determine which genetic tests are indicated in each case. In the case of de novo variations, it is important to be aware that they cannot be predicted until symptoms appear in the individual.