Type of disease: Rare conditions
Trisomy 18 is a chromosomal condition associated with severe intellectual disability and abnormalities in many parts of the body. Affected individuals often have a low birth weight; a small, abnormally shaped head; a small jaw and mouth; clenched fists with overlapping fingers; heart defects; and abnormalities of other organs. Due to the presence of several life-threatening medical problems, fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to teenage years, but with serious medical and developmental problems. Most cases of Trisomy 18 result from having three copies of chromosome 18 in each cell in the body instead of the usual two copies. Most causes are not inherited and occur by chance.