Edwards syndrome, also called trisomy 18, is a chromosomal condition that occurs when there are three copies of chromosome 18 in each cell instead of the normal two copies. Infants born with Edwards syndrome have an extremely high mortality rate—only 5 to 10 percent of these infants survive the first year of life. Some characteristics of this condition are low birth weight; a small, abnormally shaped head; small jaw; small mouth; and clenched fists with overlapping fingers. Infants born with Edwards syndrome also have mental retardation, heart defects, and other organ malformations such that most systems of the body are affected.