Mosaic Down syndrome is a variant of Down syndrome.
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What Is Mosaic Down Syndrome?
With mosaic Down syndrome, some cells have two copies of chromosome 21, and some cells have three.
Vilaiporn Chatchawal / Getty Images
If they have no other chromosome number anomalies, some cells have 46 total chromosomes and some have 47.
About 1% to 2% of people with Down syndrome have mosaic Down syndrome.
While most people with Down syndrome have similar symptoms, there is a range in severity.
Of course, though some children with typical Down syndrome scored higher than those with mosaicism.
A pregnancy with a fetus with Down syndrome has a higher risk of birth complications and stillbirth.
Causes
Human cells typically contain 23 pairs ofchromosomes(46 total), which carry genetic material.
Each sperm or egg cell typically contains only one chromosome of each pair.
Down syndrome most often takes place if an embryo is conceived with a third copy of chromosome 21.
It less commonly triggers when a part of a chromosome is translocated to another.
With mosaic Down syndrome, only some of the cells have an extra copy.
The extra chromosome can come either from the egg cell or from the sperm cell.
Trisomyis the presence of a third chromosome for a chromosome pair.
How Does Mosaicism Happen?
In general, mosaicism is a rare genetic phenomenon.
It means that the cells in the body do not have the exact same genetic pattern.
In mosaic Down syndrome, an error occurs as the embryo’s cells are making copies.
This error occurs during the very early stages of pregnancy.
It is believed that the error occurs very early during pregnancy.
Diagnosis
Down syndrome is diagnosed based on a childs physical features and with achromosome test.
Adefinitive diagnosisis made with a chromosome test.
Typically, 20 different cells are analyzed during a test.
Prenatal (before birth) testing is done withamniocentesisorchorionic villussampling.
Sampling involves the placement of a needle into the uterus (with ultrasound guidance).
Chromosome testing after birth involves laboratory analysis of a blood sample from the baby.
The chromosomal abnormalities cannot be fixed or treated at any age, even before birth.
The condition is not expected to worsen.
Coping
Living with Down syndrome can be challenging.
Attending a school that offers accommodations suitable for children and adolescents with Down syndrome can be helpful.
Some families may benefit from joining a support group that includes people with Down syndrome.
With the mosaic pattern, some cells have two copies, andsome have three.
The diagnosis is made with chromosome testing, which can be done prenatally or after birth.
Treatment is focused on the symptoms and effects, but there is no cure.
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