Which syndrome is caused by a third copy of all or part of chromosome 18?

Edwards syndrome, also known as trisomy 18, is a genetic disorder caused by a third copy of all or part of chromosome 18. Many parts of the body are affected. Babies are often born small and have heart defects. Other features include a small head, small jaw, clenched fists with overlapping fingers, and severe intellectual disability. Most cases of Edwards syndrome occur due to problems during the formation of the reproductive cells or during early development. The rate of disease increases with the mother's age.