Trisomy 18 and Edwards Syndrome

Human chromosomes come in 23 pairs, each parent supplying one chromosome in each pair. Trisomy 18 (also called Edwards syndrome) is a genetic condition in which one chromosome (chromosome 18) is a triplet instead of a pair. Like Trisomy 21 (Down syndrome), Trisomy 18 affects all systems of the body and causes distinct facial features.

Trisomy 18 occurs in 1 in 6,000 live births. Unfortunately, most babies with Trisomy 18 die before birth, so the actual incidence of the disorder may be higher. Trisomy 18 affects individuals of all ethnic backgrounds.

Trisomy 18 severely affects all organ systems of the body. Symptoms may include:

• Nervous system and brain - mental retardation and delayed development, high muscle tone, seizures, and physical malformations such as brain defects
• Head and face - small head (microcephaly), small eyes, wide-set eyes, small lower jaw, cleft palate
• Heart - congenital heart defects such as ventricular septal defect
• Bones - severe growth retardation, clenched hands with 2nd and 5th fingers on top of the others, and other defects of the hands and feet
• Malformations of the digestive tract, the urinary tract, and genitals

The physical appearance of the child at birth will suggest the diagnosis of Trisomy 18. However, most babies are diagnosed before birth by amniocentesis (genetic testing of the amniotic fluid). Ultrasounds of the heart and abdomen can detect abnormalities, as can x-rays of the skeleton.

Medical care for individuals with Trisomy 18 is supportive and focuses on providing nutrition, treating infections, and managing heart problems.

During the first months of life, infants with Trisomy 18 require skilled medical care. Due to the complex medical problems, including heart defects, and overwhelming infections, most infants have difficulty surviving to age 1 year. Advances in medical care over time will, in the future, help more infants with Trisomy 18 live into childhood and beyond.

Edited by Richard N. Fogoros, MD