The key difference between mosaic Down syndrome and Down syndrome is that individuals with mosaic Down syndrome have a combination of cells, with some cells having a normal pair of chromosome 21 and some cells having three copies of chromosome 21, while individuals with Down syndrome have 3 copies of chromosome 21 in each cell.
Aneuploidy is a genetic condition where the total number of chromosomes is generally not equal to 46. Aneuploidy can affect both autosomes and sex chromosomes. Down syndrome is the most well-known example of aneuploidy that affects autosomes. An extra copy of chromosome 21 in each cell (trisomy 21) causes this condition. There are three types of Down syndrome conditions as trisomy 21, translocation Down syndrome, and mosaic Down syndrome.
CONTENTS
1. Overview and Key Difference
2. What is Mosaic Down Syndrome
3. What is Down Syndrome
4. Similarities – Mosaic Down Syndrome and Down Syndrome
5. Mosaic Down Syndrome vs Down Syndrome in Tabular Form
6. Summary – Mosaic Down Syndrome vs Down Syndrome
What is Mosaic Down Syndrome?
Mosaic Down syndrome is a rare type of Down syndrome. Those with mosaic Down syndrome have a combination of cells. Certain cells have a normal pair of chromosome 21, while other cells contain three copies of chromosome 21. This type is only identified in about 2% of people with Down syndrome. Children with this condition may have similar features as other children with Down syndrome. However, they may have fewer symptoms due to the presence of cells with a typical number of chromosomes. The signs and symptoms may include slower speech, lower IQ (but higher IQ than individuals with other forms of Down syndrome), a flattened face, small ears, eyes that tend to slant up, shorter height, presence of white spots in the iris of eyes, sleep apnoea, ear infections, hearing loss, heart defects, immune disorders, visual impairments, and vitamin deficiencies.
Mosaic Down syndrome can be diagnosed through screening tests during pregnancy (measuring hormone levels in the blood and ultrasound) and diagnostic sound (chronic villus sampling and amniocentesis). There is no exact treatment for mosaic Down syndrome. But physical therapy, speech therapy, and occupational therapy may be very helpful in improving quality of life.
What is Down Syndrome?
Down syndrome is a disease condition caused by an extra copy of chromosome 21 in each cell. It is also known as trisomy 21. About 95% of people with Down syndrome have trisomy 21. The signs and symptoms may include a fattened face, small head, short neck, protruding tongue, palpebral fissures, unusually shaped ears, poor muscle tone, short fingers, broad and short hands with a crease in the palm, higher flexibility, white spots on the iris of the eye, and short height. The cause of Down syndrome is not known for sure, but factors like maternal age (more than 35 years) play a role.
Figure 01: Down Syndrome
Down syndrome diagnosis can be made through screening tests (blood test to measure the levels of pregnancy-associated plasma protein A and chorionic gonadotropin hormone), nuchal translucency tests, diagnostic tests (chorionic villus sampling and amniocentesis), and genetic testing. Furthermore, there is no exact cure for Down syndrome. However, speech, physical, occupational, and educational therapy may be helpful in enhancing the quality of life. In addition, there are a number of advanced research studies currently on gene therapy to treat Down syndrome.
What are the Similarities Between Mosaic Down Syndrome and Down Syndrome?
- Mosaic Down syndrome and Down syndrome are two types of aneuploidy that affect autosomes.
- Both conditions predominantly affect children.
- The cause of both conditions is not known for sure, but factors like maternal age (more than 35 years) play a role.
- Both conditions can have similar symptoms.
- They can be diagnosed through similar careening and diagnostic tests.
- There are no exact treatments for both conditions.
What is the Difference Between Mosaic Down Syndrome and Down Syndrome?
Individuals with mosaic Down syndrome have a combination of cells; some cells have a normal pair of chromosome 21, and other cells contain three copies of chromosome 21, while individuals with Down syndrome have 3 copies of chromosome 21 in each cell. Thus, this is the key difference between mosaic Down syndrome and Down syndrome. Furthermore, mosaic Down syndrome is only identified in about 2% of the people with Down syndrome, while about 95% of people with Down syndrome have trisomy 21.
The below infographic presents the differences between mosaic Down syndrome and Down syndrome in tabular form for side-by-side comparison.
Summary – Mosaic Down Syndrome vs Down Syndrome
Aneuploidy is a genetic abnormality that causes changes to the total number of chromosomes in a cell. Mosaic Down syndrome and Down syndrome are two types of aneuploidy that specifically affect autosomes. Individuals with mosaic Down syndrome have a combination of cells; some cells have a normal pair of chromosome 21, and other cells contain three copies of chromosome 21, while individuals with Down syndrome have 3 copies of chromosome 21 in each cell. So, this summarizes the difference between mosaic Down syndrome and Down syndrome.
Reference:
1. “Mosaic Down Syndrome: What You Need to Know.” Massachusetts General Hospital.
2. “Down Syndrome.” Mayo Clinic, Mayo Foundation for Medical Education and Research.
Image Courtesy:
1. “Down Syndrome (Trisomy 21)” By NIH Image Gallery (CC BY-NC 2.0) via Flickr