Ds Awareness Day#7: Types of Down syndrome

I often get asked what type of Down syndrome Peter has, but the question is really asking about his “function” level. Is he “high functioning” or “low functioning”?

Down syndrome is NOT a spectrum on which individuals having varying degrees of Down syndrome that then fall into “functioning” levels.

As with all people, individuals with Down syndrome have different strengths and weakness, which influence their ability to succeed in different areas. In addition, individuals may have other conditions that influence their ability in different environments. While some disorders occur more frequently in individuals with Down syndrome, they are not limited to these individuals.

For example, Peter has various conditions, including “Speech Apraxia”, that have limited his ability to communicate verbally. Most children his age, with Down syndrome, are able to more clearly articulate and string words together than he can now. Peter receives Speech Therapy to help him continue to develop communication. Keep following our Ds Awareness posts to learn about different therapies.

So, are there “types” of Down syndrome? 

Yes, there are three different types of Down syndrome: Standard Trisomy 21, Translocation, and Mosaicism.

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There are three types of Down syndrome.

Standard Trisomy 21/Nondisjunction is when the extra chromosome 21 in every cell. An estimated 95% of all Down syndrome cases is Standard Trisomy 21.

Translocation is caused when a piece of chromosome 21 is located on another chromosome such as chromosome 14. The person with Translocation Trisomy 21 will have 46 chromosomes but will have the genetic material of 47 chromosomes. The person with Translocation Trisomy 21 will exhibit all the same characteristics of a person with Standard Trisomy 21 since they have three copies of chromosome 21. Translocation occurs in an estimated 3% of cases of Down syndrome.

Mosaicism is when a person has a mix of cells, some containing 46 chromosomes and some containing 47 chromosomes. This occurs either because: a) The person received 46 chromosomes at fertilization but somewhere during early cell division the chromosome 21 cell pairs failed to split creating a cell with 47 chromosomes and a cell with 45 chromosomes. The cell with 45 chromosomes can not survive but the cell with 47 chromosomes will continue to divide. All cells that come from this cell will contain 47 chromosomes. b) The person received 47 chromosomes at fertilization but later during cell division the extra chromosome is lost. Mosaicism occurs in an estimated 2% of cases of Down syndrome. A person with Mosaic Down syndrome may exhibit all, some, or none of the characteristics of Down syndrome depending on the percent of cells carrying the extra chromosome and where these cells are located.

 

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