All of the cells in the body of a typical person are of the same genetic makeup. If an individual suffers from mosaicism, some off the cells in his or her body are of a different genetic makeup, and if those different cells are confined to that person’s germline cells (cells from which egg cells and sperm cells originate) then that person is said to have germline mosaicism. People with germline mosaicism will not typically suffer from any of the symptoms of the genetic disorder they have in their germline cells but they may pass the disorder on to their children.
Your family’s health history is a major factor in determining the likelihood of you, or of someone in your family having germline mosaicism. By using AccessDNA's family history tool, you will be taking an essential step towards learning your risk to have germline mosaicusm based on the diseases in your family. Click below to use the tool or scroll down to read more about germline mosaicism.
In genetics, mosaicism is characterized by the presence of one or more cell lines in a single person.
Germline mosaicism (formerly known as gonadal mosaicism) is a form of mosaicism confined to the germ and germline cells, in which a proportion of cells have a mutation, while the rest do not. Germ cells are the sex cells (egg and sperm), while germline cells are cells from which the egg and sperm orginated.
A person with germline mosaicism will not be affected with the genetic condition caused by the mutation because the mutation is not present in the rest of the body's cells. As such, genetic testing using blood or non-germline tissue samples from people with a germline mutation will be negative.
People with germline mosaicism are at risk to have children with the genetic condition caused by the mutation. If an egg or sperm cell with the mutation is used to conceive a pregnancy, that mutation will be present in all of the cells of the developing child.
Germline mosaicism can be found in disorders with any pattern of inheritance, but it is most commonly seen in conditions with autosomal dominant or X-linked patterns of inheritance. Examples of conditions in which germline mosaicism has been documented include neurofibromatosis type 1 and Duchenne Muscular Dystrophy.
Typically, a person is unaware they have germline mosaicism until they have an affected child. The recurrence risk for a parent with germline mosaicism to have another affected child is difficult to predict. Regarding conditions with autosomal dominant inheritance, studies have demonstrated that the risk to have another affected child may be low (about 1%), moderate (about 6%), or high (about 30%), depending on the proportion of germ cells (egg and sperm) with the mutation as well as the disorder itself.