Mosaic Down syndrome happens when a human body comprises a mixture of cells. Human cells consist of 46 chromosomes, and Down syndrome makes it 47.

In contrast, a Mosaic Down syndrome person has some cells with 46 chromosomes and some with 47.

What causes Down syndrome?

Down syndrome is a genetic disorder that happens due to an error in cell division at birth.

Every cell in a human body originates from one initial cell – the fertilized egg. After fertilization, the initial cell replicates itself to form the other cell copies in a process called cell division.

During this process, the DNA present in the cell also replicates itself.

However, errors are expected to happen everywhere and sometimes during cell division. This error leads to the formation of a cell with a DNA change (variation in chromosomal number).

A human body comprises 23 pairs of chromosomes (46 chromosomes) in each cell. One in each pair is passed to us from our mother and father, respectively.

Down syndrome is caused when there is an extra copy of chromosome 21, resulting in 47 chromosomes.

Mosaic syndrome happens when this extra copy of a chromosome is present only in some of the cells rather than in all.

This makes the human body have a mixture of chromosomes, where some cells have 46 chromosomes, and some have 47.

Mosaic Down Syndrome

How is Mosaicism caused with Down syndrome?

Mosaicism in Down syndrome can be formed in two different ways.
  • When the initial call coming from a parent has an extra copy of a chromosome, and sometime during the cell division, this extra pair of chromosomes gets lost.
  • The initial cell will have the normal pair of chromosomes, and sometime during the cell division, one of the 21st chromosomes gets duplicated.

Mosaic Down Syndrome Symptoms

People with simple Down syndrome and Mosaic Down syndrome share similar characteristics.

Physical characteristics of Mosaic Down syndrome:

  • Absence of nasal bone bridge 
  • Poor muscle tone
  • Abnormally shaped eyes and ears
  • Height and weight variation
  • Broader forehead
  • Protruding tongue
  • Excess skin at the back of the neck

Intellectual and Development Disabilities with Mosaic Down syndrome:

  • Lower IQ
  • Delayed speech and language development
  • Sleep apnea
  • Delayed toilet training
  • Attention problems

Is mosaic Down syndrome less severe?

Some studies reveal that Mosaicism people show better cognitive skills and clinical features when compared to the other types of trisomy 21.

With Mosaicism, not all cells are affected by the extra chromosome.

Here, the human body has a combination of normal cells and chromosomally affected ones, leading to fewer symptoms of the syndrome.

How is Mosaic Down Syndrome Diagnosed?

Mosaicism is a type of Down syndrome that can be identified as a percentage during one of the confirmatory tests below:

Amniocentesis: is an invasive procedure done between the 15th and 20th weeks of gestation. Amniotic fluid from the uterus is used to study your baby’s chromosome karyotype.

Chorionic Villus Sampling (CVS): is an invasive procedure done between the 10th and 23rd weeks of gestation. Your placental tissues are extracted to study your baby’s genetic makeup.

NIPT:  is a non-invasive procedure done between the 9th and 10th of gestation. Maternal blood is collected to study your baby’s chromosome karyotype.

How is Mosaic Down syndrome Calculated?

Mosaic Down syndrome is usually calculated as a percentage. For this, a sample of 20 different cells is analyzed by your doctor during the chromosome study.
Now, for example:

  • 5 out of 20 cells have the normal 46 chromosomes.
  • And 15 out of 20 cells are identified to have an extra copy of chromosome 21.
    Then, the result will tell you that your baby has 75% of Mosaicism.

Health issues caused by Mosaic Down syndrome

Due to low metabolic rate and immunity, Down syndrome people are prone to infections and other health issues like,

  • Ear infections
  • Hearing loss
  • Visual impairments
  • Weight gain
  • Diabetes
  • Gastrointestinal disorders
  • Epilepsy
  • Celiac disease
  • Leukaemia
  • Dental problems

Congenital heart disease is one of the common major health issues faced by Down syndrome people.

This can be mild or severe and can be diagnosed even before birth. Discuss with your doctor the ways to treat this if any of your diagnostic test shows positive.

Mental Health Problems in Mosaic Down syndrome:

Research by Virginia Commonwealth University reported that more than 50% of Mosaic Down syndrome people under study showed elevated depression, and 74% reported elevated anxiety.

Mosaicism Treatment

There is no treatment to cure Mosaic Down syndrome or any trisomy 21. But, early intervention can make life easier for a child with this syndrome

Mosaicism Treatment

  • Get regular physical check-ups
  • Lookout signs for major health and mental issues.
  • Get assistance for Cognitive and Behavioral development
  • Encourage your child to socialize with peers
  • Stand up to bullies

What is the life expectancy of Mosaic Down syndrome?

It is usually said that the life expectancy of Down syndrome is between 50 to 60years. However, proper interventions and therapies in recent times have given Down syndrome people a much higher life expectancy than in the past.

Common Question by Parents of a child with Mosaic Down syndrome

  1. What is the IQ level of a Mosaic Down syndrome kid?

The IQ level of Mosaic down syndrome is higher than people with regular trisomy 21. Most of the children get an average IQ score between 60 to 70, and some might have the capabilities to score above 70.

2. Will my child need specialized therapies?

There is no way to determine how a child with Mosaicism will be affected. But, it’s always the best idea to give therapy support to any Down syndrome child as early as possible.

It is not true that they can’t build their skills. It’s just that they need some extra support and time to develop.

3. As a parent, what steps should I take to assist my kid’s health with Down syndrome?

Have regular health check-ups. Closely monitor signs for heart defects and other conditions like feeding troubles, cataracts, digestion issues, hypothyroidism, leukaemia, wheezing, and infections.

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