What are the types of down’s syndrome?

Medically Reviewed by Checkmark Medically Reviewed By: Dr. Sravanthi Sunkaraneni
Down's syndrome can be of three types. Trisomy 21 is seen in 95% of cases, which is characterized by three chromosomes at position 21. Second, mosaicism (1%), is characterized by one of two or more genetically diverse sets of cells. And the third form is translocation (4%), defined by an additional whole or partial copy of chromosome 21 attaching with another chromosome, generally chromosome 14.


There are three types of down’s syndrome as enlisted by The National Down Syndrome Society, i.e., Trisomy 21, Mosaic, and Translocation.

Trisomy 21 is a rare genetic condition where an extra chromosome is present. Generally, a person inherits 23 chromosomes from each parent, for a total of 46 chromosomes. Babies with down’s syndrome, however, end up with three chromosomes at position 21 instead of the usual pair. This type of down’s syndrome accounts for 95% of the cases, as per the Down’s Syndrome Society.

Mosaicism is the least common form of down’s syndrome and accounts for only about 1% of all cases.” According to Yale Medicine, “Mosaicism occurs when a person has two or more genetically different sets of cells in his or her body. If those abnormal cells begin to outnumber the normal cells, it can lead to disease that can be traced from the cellular level to affected tissue, like skin, the brain, or other organs”.

Translocation accounts for about 4% of cases of down’s syndrome. The Down Syndrome Society states, “The total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14, causing the peculiar characteristics of down’s syndrome”.

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Disclaimer
Medical Science is an ever evolving field. We strive to keep this page updated. In case you notice any discrepancy in the content, please inform us at [email protected]. You can further read our Correction Policy here. Never disregard professional medical advice or delay seeking medical treatment because of something you have read on or accessed through this website or it's social media channels. Read our Full Disclaimer Here for further information.

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