Trisomy 18
![Infant with trisomy 18](https://upload.wikimedia.org/wikipedia/commons/4/45/Trisomy_17-18_2.jpg)
Most cases of trisomy 18 occur due to problems during the formation of the reproductive cells or during early development. The chance of this condition occurring increases with the mother's age. Rarely, cases may be inherited. Occasionally, not all cells have the extra chromosome, known as mosaic trisomy, and symptoms in these cases may be less severe. An ultrasound during pregnancy can increase suspicion for the condition, which can be confirmed by amniocentesis.
Treatment is supportive. After having one child with the condition, the risk of having a second is typically around one percent. It is the second-most common condition due to a third chromosome at birth, after Down syndrome for a third chromosome 21.
Trisomy 18 occurs in around 1 in 5,000 live births. Many of those affected die before birth. Some studies suggest that more babies that survive to birth are female. Survival beyond a year of life is around 5–10%. It is named after the English geneticist John Hilton Edwards, who first described the syndrome in 1960. Provided by Wikipedia