Q91.1: Trisomy 18, mosaicism (mitotic nondisjunction)

You have a congenital disorder, which means you were born with it. This disorder is called Trisomy 18.

When beginning its development, every single cell in the body contains a complete blueprint of the body. This blueprint consists of genetic information. The genetic information is encrypted in the chromosomes. Every human cell normally contains 23 chromosome pairs, i.e. a total of 46 chromosomes.

Trisomy 18 is a congenital disorder, where you have one chromosome more than normal. Instead of 2 copies of chromosome 18, you have 3 copies of chromosome 18. This disorder is therefore called Trisomy 18. In some cases, only a part of chromosome 18 is present three times. There are cells in your body where chromosome 18 appears twice. However, you also have cells in the body where chromosome 18 appears three times. This is called Mosaic Down syndrome, or mosaicism.

Trisomy 18 is a very serious condition. Trisomy 18 can vary greatly in severity. Certain visible features are apparent, for example, on the face and hands. The head is smaller than normal. You may find it difficult to breathe or swallow. You can also have diseases affecting the heart and kidneys. Trisomy 18 can also cause you to have many other symptoms.