Mosaic Down Syndrome: Symptoms and Diagnosis (2024)

Mosaic Down syndrome, or mosaicism, is a rare form of Down syndrome. People with this form may have fewer symptoms of Down syndrome.

Down syndrome is a genetic disorder that results in an extra copy of chromosome 21. People with mosaic Down syndrome have a mixture of cells. Some have two copies of chromosome 21, and some have three.

Mosaic Down syndrome occurs in about 2 percent of all Down syndrome cases. People with mosaic Down syndrome often, but not always, have fewer symptoms of Down syndrome because some cells are normal.

Down syndrome is a genetic disorder in which some, or all, of a person’s cells have an extra chromosome.

All normal human cells have 46 chromosomes, except the egg and sperm, which normally have 23. These sex cells are formed by division (called meiosis). When an egg is fertilized, these two cells join, normally giving the embryo 23 chromosomes from each parent for a total of 46 chromosomes.

Sometimes an error occurs in this process, causing the wrong number of chromosomes to occur in the sperm or egg. A healthy baby has two copies of chromosome 21 in each cell. People with Down syndrome have three. Any cell replicated from the flawed cell will also have the wrong number of chromosomes.

People with mosaic Down syndrome have a mixture of cells. Some cells have a normal pair of chromosome 21, and other cells contain three copies. This usually happens because the division problem that causes the extra copy of chromosome 21 happens after fertilization.

Irregular chromosome copies change the genetic makeup of a baby, ultimately affecting their mental and physical development.

People with Down syndrome typically have:

Down syndrome is sometimes accompanied by a number of other health problems, including:

These symptoms are also common in people with mosaic Down syndrome. However, they may have less of these symptoms. For example, people with mosaic Down syndrome typically have a higher IQ than those with other forms of Down syndrome.

Doctors can perform tests to screen for Down syndrome during pregnancy. These tests show the likelihood that the fetus will have Down syndrome and can identify health problems early.

Screening tests

Screening tests for Down syndrome are offered as routine testing during pregnancy. They’re usually provided during the first and second trimesters. These screens measure hormone levels in the blood to detect abnormalities and use an ultrasound to look for irregular fluid buildup in the baby’s neck.

Screening tests only provide the likelihood of a baby developing Down syndrome. It cannot diagnose Down syndrome. They can determine, though, whether more tests are needed to confirm the diagnosis.

Diagnostic tests

Diagnostic tests can confirm if your baby has Down syndrome before it’s born. The two most common diagnostic tests are chorionic villus sampling and amniocentesis.

Both tests take samples from the uterus to analyze chromosomes. Chorionic villus sampling uses a sample of the placenta to do this. This test can be completed in the first trimester. Amniocentesis analyzes an amniotic fluid sample surrounding the growing fetus. This test is typically performed in the second trimester.

Mosaic Down syndrome is typically described through a percentage. To confirm mosaic Down syndrome, doctors will analyze chromosomes from 20 cells.

If 5 cells have 46 chromosomes and 15 have 47 chromosomes, a baby has a positive mosaic Down syndrome diagnosis. In this case, the baby would have a 75 percent level of mosaicism.

There’s no treatment for mosaic Down syndrome. Parents can detect the condition before birth and prepare for any associated birth defects and health complications.

Life expectancies for people with Down syndrome are much higher than in the past. They can now be expected to live to more than 60 years of age. Furthermore, early physical, speech, and occupational therapies can provide people with Down syndrome a higher quality of life and improve their intellectual abilities.

Mosaic Down Syndrome: Symptoms and Diagnosis (2024)

FAQs

What is the diagnostic criteria for mosaic Down syndrome? ›

This test is typically performed in the second trimester. Mosaic Down syndrome is typically described through a percentage. To confirm mosaic Down syndrome, doctors will analyze chromosomes from 20 cells. If 5 cells have 46 chromosomes and 15 have 47 chromosomes, a baby has a positive mosaic Down syndrome diagnosis.

What is the life expectancy of someone with mosaic Down syndrome? ›

Currently we have no research that indicates individuals with mosaic Down syndrome will live longer than their peers with Down syndrome. Current research suggests that individuals with Down syndrome live to 55 yrs of age. The oldest living woman with mosaic Down syndrome lived to the age of 83 years old.

Can people with mosaic Down syndrome have normal intelligence? ›

Most individuals with Down syndrome have mild (IQ: 50–69) or moderate (IQ: 35–50) intellectual disability with some cases having severe (IQ: 20–35) difficulties. Those with mosaic Down syndrome typically have IQ scores 10–30 points higher than that.

What is the major symptoms of mosaic disease? ›

Mosaic symptoms are variable but commonly include irregular leaf mottling (light and dark green or yellow patches or streaks). Leaves are commonly stunted, curled, or puckered; veins may be lighter than normal or banded with dark green or yellow.

How do you diagnose mosaic syndrome? ›

When a baby is born with Down syndrome, the healthcare provider takes a blood sample to do a chromosome study. Mosaicism, or mosaic Down syndrome, is diagnosed when there is a mixture of two types of cells. Some have the usual 46 chromosomes, and some have 47.

Can you look normal with mosaic Down syndrome? ›

Some of the children with Mosaic Down syndrome that we know do not actually look as if they have Down syndrome - the usual physical features are not obvious. This raises some important and difficult social issues and identity issues for both parents and children, which parents have discussed with us.

Can mosaic Down syndrome go undiagnosed? ›

Mosaic Down syndrome

You can't tell what type of Down syndrome someone has by how they look. The effects of all three types are very similar, but someone with mosaic Down syndrome may not have as many symptoms because fewer cells have the extra chromosome. So it's possible to have undiagnosed mosaic Down syndrome.

Who is the girl with mosaic Down syndrome? ›

For Ashley Zambelli, a surprise diagnosis allowed her to have an even more special bond with her children. The Michigan-based mom, 23, recently found out she has Mosaic Down syndrome, a condition in which a person has some cells with extra chromosomes and some cells with the typical number.

How rare is mosaic downs? ›

One chromosome of each pair comes from the father, and one chromosome of each pair comes from the mother. An extra copy of chromosome 21 causes the differences we see in people with Down syndrome. About 1 to 2% of people with Down syndrome have mosaic Down syndrome.

What IQ do people with Down syndrome have? ›

The average intelligence quotient (IQ) of children with DS is around 50, ranging between 30 and 70. Remarkably, a small number of patients have a profound degree of ID, whereas others have a mild degree despite the absence of any genetic, cultural or familial favoring or disfavoring causes.

What's the difference between Down syndrome and mosaic Down syndrome? ›

Mosaic means mixture or combination. In this type, some cells have three copies of chromosome 21, but other cells have the typical two copies. People with mosaic Down syndrome may have fewer features of the condition. This type accounts for about 2% of people with Down syndrome.

What is the mildest form of Down syndrome? ›

Mosaicism is the least common form of Down syndrome and accounts for only about 2% of all cases of Down syndrome (Facts about Down syndrome, 2021). Research has indicated that individuals with mosaic Down syndrome may have fewer characteristics of Down syndrome than those with other types of Down syndrome.

Can people with mosaic Down syndrome drive? ›

Driving. Those with Down syndrome can drive if they can pass the necessary written and practical exams.

Can mosaic Down syndrome go unnoticed? ›

Some of the children with Mosaic Down syndrome that we know do not actually look as if they have Down syndrome - the usual physical features are not obvious. This raises some important and difficult social issues and identity issues for both parents and children, which parents have discussed with us.

What is an example of mosaicism? ›

The term "mosaicism" is used to describe the presence of more than one type of cell in a person. For example, a person may have some of the cells in their body with 46 chromosomes, while other cells in their body have 47 chromosomes. An example of mosaicism is mosaic Down syndrome.

What are the symptoms of mosaic chromosomes? ›

Signs & Symptoms

However, the disorder is often characterized by (1) growth and developmental delays, (2) asymmetric body development, and (3) congenital heart diseases. Intrauterine growth restriction (IUGR) and postnatal growth failure were found in more than 70% patients with mosaic trisomy 22.

How do you know if you have mosaic Turner syndrome? ›

Signs of Turner syndrome and mosaic Turner syndrome
  1. Height usually under 5 feet.
  2. Droopy (heavy) eyelids (ptosis)
  3. Differences in ear shape and position.
  4. Webbed neck (extra skin)
  5. Arms or feet that are puffy (lymphedema)
  6. Often, broad chest.
  7. High-arched roof of the mouth.
  8. Teeth that are crowded.
Jul 8, 2019

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