Around 1–2 % of people with Down syndrome have mosaic Down syndrome, which means only around 120–240 people in Australia live with this rare type of Down syndrome.

Mosaicism occurs when a person has two or more genetically different sets of cells in their body.

People with the more common form of Down syndrome, Trisomy 21, have 3 copies of the additional 21st chromosome in each cell.

However, people with mosaic Down syndrome have some cells with an additional 21st chromosome, while other cells have two copies rather than three.

Mosaicism occurs when the chromosomal variation occurs after fertilization. As with Trisomy 21, people with mosaic Down syndrome are all unique individuals with a range of strengths and interests.

Some though not all people with mosaic Down syndrome have fewer of the physical features that can be associated with Down syndrome, but most children will experience delays in meeting developmental milestones.

Whilst some people with mosaic Down syndrome may experience less of the developmental and physical impacts of Trisomy 21, other people with mosaic Down syndrome will experience many of these.

The degree of impact will depend upon a range of other factors, including the level of mosaicism.

In this episode, we will hear from a range of people about mosaic Down syndrome, including a person with the condition, and a couple of parents who discuss their journey to diagnosis.

Click on the links for further information:

International Mosaic Down Syndrome Association

Stanford Children's Health

Down Syndrome Australia Information

Needs of Children with Mosaic Down Syndrome

This podcast is a production of Down Syndrome Queensland.

If you have a question, would like more information on any of our episodes, or have suggestions for future topics, send us an email - engagement@downsyndrome.qld.org.au.

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