Mosaicism is the name given to a type of genetic failure during the development of the embryo inside the maternal uterus, in which the person starts to have 2 distinct genetic materials, one that is formed by the junction of the egg with the parents' sperm, and another that arises due to a mutation of a cell in the course of the embryo's development.
Thus, the person will develop a mixture of cells, with a percentage of normal cells and another percentage of cells with the mutation, as shown in the following figure:
Main features
Mosaicism happens when a mutation occurs in an embryo cell, usually the loss or duplication of a chromosome, which causes the person to develop his organism with 2 types of cells, and 2 types of genetic material. This mutation can be of 2 types:
- Germinative or Gonadal: affects sperm or eggs, with alterations capable of being transmitted to the children. Some examples of diseases caused by changes in the germ cells are Turner's syndrome, imperfect osteogenesis and Duchenne muscular dystrophy;
- Somatic: in which cells from any other part of the body carry this mutation, the person may or may not develop physical changes caused by it. Thus, the physical expression of the mutation depends on which and how many cells in the body are affected. Somatic mosaicism can be passed from parents to children, and some examples of diseases caused are Down's syndrome and neurofibromatosis.
Mixed mosaicism, on the other hand, occurs when the person has both types of mosaicism, both germinative and somatic.
Mosaicism is different from chimerism in that, in this situation, the embryo's genetic material is duplicated by the fusion of 2 different embryos, which become one. Learn more about this situation in chimerism.
Consequences of mosaicism
Although many cases of mosaicism do not cause symptoms or any consequence for the health of the person, this situation can cause the appearance of several complications and diseases for the carrier person, and some examples are:
- Predisposition to cancer;
- Changes in growth;
- Predisposition to spontaneous abortions;
- Changes in the pigmentation pattern of the skin;
- Ocular heterochromia, in which the person can have one eye of each color;
- Down's syndrome;
- Turner syndrome;
- Osteogenesis imperfecta;
- Duchenne muscular dystrophy;
- McCune-Albright syndromes;
- Pallister-Killian syndrome;
- Proteus syndrome.
In addition, it has been observed that mosaicism increases the predisposition to degenerative neurological diseases, such as Alzheimer's or Parkinson's, for example.
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