Trisomy 18 Facts*
*Trisomy 18 facts Medically Edited by: Melissa Conrad Stöppler, MD
- Trisomy 18 is a rare genetic condition that causes severe intellectual impairment and birth defects in babies who are afflicted with the disorder. Trisomy 18 is also known as Edwards syndrome.
- About 1 in 5,000 newborns has trisomy 18. Approximately 80% of babies who have the condition are female.
- About 90% to 95% of babies who are born with the condition will not live past one year of age.
- Trisomy 18 results from having three copies of chromosome 18 instead of two.
- Mosaic trisomy 18 refers to a condition in which only some cells carry an extra copy of chromosome 18.
- Most cases of trisomy 18 are not inherited. Trisomy 18 often results when a random error causes a sperm or egg cell to gain an extra copy of chromosome 18.