Down syndrome is one of the most prominent genetic disorders, where the presence of an extra chromosome 21 is the main cause of this syndrome. Also, Down syndrome is not just one type, as is common, but its type differs based on how this extra chromosome exists.
Mosaic Down syndrome is a type of Down syndrome, which is characterized by a set of characteristics and traits that may make it the mildest and least severe compared to other types of Down syndrome. (1)
Mosaic Down syndrome is a rare type of Down syndrome, distinguished by the fact that some of the body's cells contain an extra copy of chromosome 21, while other cells are normal. This diversity in cells is called the "mosaic pattern", where a person has a mix of normal cells and cells with trisomy 21. (1)
As with other types of Down syndrome, the problem that occurred was a defect during early cell division after fertilization.
In mosaic Down syndrome specifically, some cells divide normally, while others do not divide normally, and thus some have an extra chromosome 21. This leads to two types of cells in the body: (2)
Mosaic Down syndrome is the rarest type of Down syndrome, representing only about 2% of all Down syndrome cases.
While the most common type of Down syndrome is full trisomy 21, where all of the body's cells have an extra chromosome 21. (1)
All types of Down syndrome share the same physical and health symptoms, whether it is in terms of: distinctive facial features, impaired cognitive abilities, and potential accompanying health problems.
However, research indicates that individuals with mosaic Down syndrome may have less pronounced features and symptoms compared to those with other types of Down syndrome. However, this finding cannot be absolutely generalized, because the abilities of people with Down syndrome vary greatly from person to person. Each individual is a unique case, and the severity of symptoms and health and developmental challenges may vary among them. (3)
When a child with Down syndrome is born, doctors perform a chromosome analysis using a blood sample. Mosaic Down syndrome is diagnosed when there is a mix of two types of cells (normal / and those containing an extra chromosome). (3)
How is the percentage of mosaicism determined?
When a chromosome analysis is performed, a sample of a certain number of cells is examined, for example, 20 cells:
Then the percentage of mosaicism is 75% (15 cells out of 20).
However, this percentage may vary from one part of the body to another. The proportion of affected cells may be different in the blood, muscles, brain, or skin.
Note: There are studies trying to find out if the proportion of affected cells affects the level of intelligence or the likelihood of congenital heart defects, but so far, there is no conclusive evidence that the percentage of mosaicism can predict the severity of symptoms or the health effects of the child. (3)
Children with mosaic Down syndrome should be provided with a special educational and medical environment, and it is important to provide them with appropriate support and help them to achieve their potential, and psychological support for the families of those affected should not be neglected.
It is important to realize that special education programs and early medical interventions are the most important fundamental factors that help in improving and developing the quality of life for those with the syndrome. (2)
In our pediatrics department at Dr. Sulaiman Faqih Hospital, we provide comprehensive care for children with Down syndrome, including health follow-up, developmental and rehabilitation programs, and medical and educational consultations to help you provide the best environment for your child.
