Trisomy 18

Edwards’ syndrome, also known as trisomy 18, is a genetic disorder caused by the presence of a third copy of all or part of chromosome 18.[3] Many parts of the body are affected.[3] Babies are often born small and have heart defects.[3] Other features include a small headsmall jaw, clenched fists with overlapping fingers, and severe intellectual disability.[3]

Most cases of Edwards’ syndrome occur due to problems during the formation of the reproductive cells or during early development.[3] The rate of disease increases with the mother’s age.[3] Rarely, cases may be inherited from a person’s parents.[3] Occasionally, not all cells have the extra chromosome, known as mosaic trisomy, and symptoms in these cases may be less severe.[3] An ultrasound during pregnancy can increase suspicion for the condition, which can be confirmed by amniocentesis.[2]

Treatment is supportive.[2] After having one child with the condition, the risk of having a second is typically around one percent.[2] It is the second-most common condition due to a third chromosome at birth, after Down syndrome.[4]

Edwards’ syndrome occurs in around 1 in 5,000 live births.[3] Some studies suggest that more babies that survive to birth are female.[2] Many of those affected die before birth.[3] Survival beyond a year of life is around 5–10%.[3] It is named after English geneticist John Hilton Edwards, who first described the syndrome in 1960.[5]

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