We know that our bodies are made up of trillions of cells. We usually think of each of these cells as having the same set of genetic information, like many copies of the same blueprint. But sometimes this can be a little different. Imagine that some cells in your body have the same genetic blueprint, and some cells have a slightly different genetic blueprint. That's what we call mosaicism in medicine.
Simply put, what is Mosaicism?
Simply put, Mosaicism is the presence of two or more genetically different groups of cells in the same person's body. This is like mosaic art. Just as small tiles of different colors and shapes come together to create a beautiful picture, what happens here is that cells with different genetic makeup come together to form a single body.
A good example of this is the difference in the number of chromosomes. A healthy person has 46 chromosomes in each cell. However, in a person with mosaicism, some cells have 46 chromosomes, while another group of cells may have a different number, such as 47 or 45 chromosomes. This genetic difference can cause certain health problems at birth, and sometimes problems later in life.
What diseases can be associated with mosaicism?
Mosaicism can cause a variety of diseases. But the effects of this vary greatly from person to person. It depends on the percentage of abnormal cells in the body and in which organs those cells are located. Let's look at some of the main diseases associated with this.
| Condition | Impact and common features |
|---|---|
| Mosaic Down syndrome | This is a form of Down syndrome. It can cause intellectual disability, muscle weakness, and a flat face. Some children may also have heart disease, digestive problems, and thyroid problems. |
| Pallister-Killan mosaic syndrome | Even in this condition, muscle weakness, intellectual delays, thinning hair, irregular skin pigmentation, and other birth defects are seen. |
| SOX2 anophthalmia syndrome | This is a very rare condition that can cause severe complications such as the baby being born without eyes, seizures, brain development problems, and delayed physical development. |
| Trisomy 18 (Mosaic) | This is a condition where the baby's growth is stunted in the womb. The baby may be born with a smaller than normal head, heart defects, and other organ defects. Unfortunately, many babies with this condition do not survive beyond their first year. |
In addition, mosaicism may be associated with other chromosomal abnormalities, such as Turner syndrome, and some types of cancer, especially blood cancers.
Why does this situation occur?
This actually happens most of the time by chance. This is not due to anyone's fault. Imagine, after the mother's egg is fertilized by the father's sperm, the first cell (zygote) that forms begins to divide. In this way, as one cell divides into two, two, four, four, eight, etc., the embryo develops.
During this cell division, each new cell must receive an exact copy of the chromosomes of the original cell. But very rarely, an error can occur during this copying process. The error can cause the new cell to have a different number of chromosomes. When the defective cell continues to divide, the body produces a generation of cells with an abnormal genetic makeup. The original, healthy cells also continue to divide, so that eventually the body has two sets of cells.
- High-level mosaicism: If this defect occurs very early in embryonic development, a large percentage (50% or more) of abnormal cells spread throughout the body.
- Low-level mosaicism: If the defect occurs at a later stage of development, the number of cells affected is small.
Are there main types of mosaicism?
Yes, Mosaicism can be classified into several main types. Understanding this can help you gain a better understanding of the nature of the condition.
| Classification | Simple explanation |
|---|---|
| Depending on the type of cell affected | |
| Somatic Mosaicism | Here, the genetic change is only in the body's normal cells (somatic cells). That is, cells in organs such as the skin, brain, and heart. Importantly, this condition does not affect reproductive cells (eggs and sperm), so it is not inherited from parents to children. |
| Germline Mosaicism | The genetic change is only in the germline cells, that is, in the eggs or sperm. Therefore, even if the parents do not have any symptoms, their children are at risk of inheriting this genetic condition. |
| According to the spread in the body | |
| General Mosaicism | Here, abnormal cells are present throughout the child's entire body. |
| Confined Mosaicism | Here, the abnormal cells are not found throughout the body, but are limited to a specific organ or tissue, such as the brain, heart, or liver. For example, there is a condition called Confined Placental Mosaicism, which is limited to the placenta. |
How do doctors diagnose this condition?
Special genetic testing is required to diagnose mosaicism.
- Prenatal Diagnosis: If there is a suspicion that a baby has Mosaicism during pregnancy, doctors may recommend special tests. Amniocentesis (testing the amniotic fluid surrounding the baby) and Chorionic Villus Sampling (CVS) (testing a small piece of tissue from the placenta) are two such tests.
- Postnatal testing: After the baby is born, the condition can be diagnosed through blood tests, skin biopsy, etc. Sometimes, it may be necessary to test two different types of tissue to confirm the exact condition.
Especially in methods such as in-vitro fertilization (IVF), it is possible to test for genetic defects through a test called Preimplantation Genetic Screening (PGS) before the embryo is implanted in the mother's uterus.
Is there a treatment for mosaicism?
This is a problem that many people have. In fact, there is currently no way to reverse or cure the underlying genetic condition called Mosaicism. That is, it is not possible to eliminate the abnormal cells and replace them with normal cells.
But, most importantly, there are various ways to manage and treat the health problems and symptoms caused by Mosaicism.
Treatment options depend on the condition affecting each individual. For example, a child with Mosaic Down syndrome may benefit from speech therapy and physiotherapy to help them develop and improve their abilities. If there is a heart condition, treatment is given to address the underlying cause. This means that treatment is not aimed at the Mosaicism, but at the consequences of the condition. It is important to talk to your doctor about the best treatment plan for you or your child.
What will the future be like with this situation?
It is difficult to predict the prognosis of someone with mosaicism, as it depends on many factors. The main ones include:
- What is the percentage of abnormal cells? (Percentage of abnormal cells)
- Which organs/tissues are affected?
- Severity of the associated condition.
A person with a very low percentage of abnormal cells (low-level mosaicism) may live a completely healthy life without any symptoms. Another person may have minor problems. If the percentage of abnormal cells is high and major organs such as the brain and heart are affected, the problems can increase.
Therefore, rather than being unnecessarily fearful about this, it is very important to see a specialist, receive genetic counseling , and gain a clear understanding of your or your child's specific situation.
Take-Home Message
- Mosaicism is the presence of more than one genetically distinct group of cells in the same person's body.
- This is not anyone's fault, but rather a random error that occurs during cell division during the early stages of embryonic development.
- The effects of mosaicism vary greatly from person to person. Some may be unaffected, while others may develop serious health problems.
- Although there is no cure for this condition, there are very effective treatments to manage the symptoms and health problems that result from it.
- If you or someone in your family has any doubts or questions about Mosaicism, the best thing to do is to discuss it openly with your doctor .
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