Trisomy 18

Trisomy 18, also called Edwards syndrome, is a chromosomal condition caused by having three copies of chromosome 18 in each cell in the body instead of the usual two copies. The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 18.

Due to the presence of several life-threatening medical problems, approximately 30% of babies make it to full term.  Only 50% of those children are born alive.   The median life expectancy is 1 month, only 5-10% live to their first birthday.

Trisomy 18 occurs in about 1 in 5,000 newborns. Approximately 80 percent of newborns affected by this disorder are female. Although women of all ages can have a child with trisomy 18, the chance of having a child with this condition increases as a woman gets older.

Most cases of trisomy 18 are not inherited, but occur as random events during the formation of eggs and sperm. An error in cell division called nondisjunction results in a reproductive cell with an abnormal number of chromosomes. For example, an egg or sperm cell may gain an extra copy of chromosome 18. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra chromosome 18 in each of the body’s cells.

The type of Edwards Syndrome that Alexandria has is not inherited.

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