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A cell with three copies of a particular chromosome, for example trisomy 18 (Edwards syndrome) in which a cell has an extra copy of chromosome 18.

Use in clinical context

Trisomy is a type of aneuploidy. There are five conditions caused by different trisomies – trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau’s syndrome), trisomy X (Triple X syndrome), and Klinefelter syndrome (XXY). For other chromosomes, an extra copy at fertilisation is not viable, and the embryo will be aborted early during development. As with other aneuploidies trisomy can occur in cancer, influencing tumour growth and progression and response to therapy. Trisomy can be identified using karyotyping or sequencing.

Last updated on 30th May, 2019