Mosaic Down Syndrome is a rare form of Down Syndrome that occurs when some cells have an extra copy of chromosome 21.
About 1 to 2 % of individuals have Mosaic Down Syndrome.
Mosaic Down syndrome is diagnosed by genetic testing of the baby’s blood. 20 to 25 cells are examined and if some have trisomy 21 and others don’t, then the diagnosis of mosaicism is made. This test can only determine the level of mosaicism in the blood cell line
There is no known cause of Down Syndrome. When cell division is happening in the womb, some cells receive an extra copy of chromosome 21 and some do not. Individuals with Mosaic Down Syndrome will have cells with two and three copies of chromosome 21.
Symptoms Of Mosaic Down Syndrome
While people with the more common trisomy 21 Down syndrome have an extra chromosome in all of their cells, people with mosaic Down syndrome only have an extra chromosome in some cells.
As a result, people with mosaic Down syndrome may have fewer characteristics of the condition than people with trisomy 21 Down syndrome.
The physical characteristics include:
- almond-shaped eyes slant upward
- A short neck (shorter than average)
- Flattened facial profile
- small ears
- Low muscle tone
- a tongue that sticks out of the mouth
Down syndrome can also involve:
- disorders of the eyes
- Trouble hearing
- a compromised immune system
- neurological disabilities
What does Mosaicism mean for my child?
Individuals with this type of Down Syndrome will share most of the health issues and challenges as people with other types of Down Syndrome. It is not possible to predict how a child with Down Syndrome will develop.
Is it possible to have another child with Down Syndrome?
Down Syndrome occurs by chance and cannot be passed to children.
Although it can happen, the chances of having another baby with Down Syndrome are approximately 1%
Down Syndrome is the most common chromosomal condition.
Genetic counseling is the best way to determine genetic predispositions before trying for a child.
