Mosaicism is a condition in which cells within the same person have a different genetic makeup. This condition can affect any type of cell, including blood cells, egg and sperm cells, and skin cells. Mosaicism occurs when there is an error in cell division very early in the development of the unborn baby. This can happen when new cells form and the chromosomes replicate themselves in order for the new cells to have the same number of chromosomes as the original cell. Mosaicism may be caused by an error in mitosis, which is the dividing of body cells. It’s how a baby in the womb grows. Mitosis causes the number of chromosomes to double to 92, and then split in half back to 46. This process repeats constantly as the baby grows. Mitosis continues throughout your lifetime. It replaces skin cells, blood cells, and other types of cells that are damaged or naturally die. If there is an error in mitosis, a cell doesn’t split evenly into 2 cells. The result is that some cells have the normal number of 46 chromosomes, and other cells have more (47) .
Mosaicism can cause health problems in the body if abnormal cells begin to outnumber the normal cells. Symptoms vary and are very difficult to predict. Symptoms may not be as severe if a person has both normal and abnormal cells. Genetic testing can diagnose mosaicism. The effect mosaicism has on a person’s health will depend on the level of mosaicism present at birth. Mosaicism has been linked to various pathologies including Turner syndrome, which is a chromosomal abnormality, and to various forms of cancer. People with a low number of abnormal cells may be only mildly affected. They may not discover that they have mosaicism until they give birth to a child who has the non-mosaic form of the disease.
