What is Trisomy 18?

Trisomy 18 is a congenital disorder that results from an extra copy of chromosome 18. The third chromosome severely impairs organ and brain development in the fetus, and often leads to fatal complications within the first few weeks of life. Infants who survive into childhood are often physically deformed and have serious cognitive deficiencies. The primary focus of treatment for a patient with trisomy 18 is to reduce pain and repair structural anomalies of the heart and lungs, giving the baby the best possible chances of surviving past infancy.

Healthy babies are born with 23 pairs of chromosomes, receiving equal numbers from each parent. An infant who suffers from this disorder acquires an additional copy of the chromosome from one parent, usually the mother, due to a second round of meiosis during the earliest stages of development. Trisomy 18 is the second most common chromosomal defect, though it is much rarer than trisomy 21, the disorder responsible for Down syndrome. It is about three times as likely to affect female fetuses than males.

Symptoms that are commonly seen in an infant with trisomy 18 include a smaller than average head, low birth weight, and a concave chest cavity. Babies often have congenital defects that impair their ability to feed and breathe without medical assistance. Internal organs may be displaced or deformed, and most infants have underdeveloped brains. It is also common for a baby to have constantly clenched hands, crossed legs, and oddly shaped feet. Additional physical symptoms vary from patient to patient.

Obstetricians may be able to notice signs of trisomy 18 before a baby is born via ultrasound images. After an infant is born, genetic testing of a sample of skin or blood cells can confirm the presence of an extra chromosome. Once the disorder has been diagnosed, specialists can create a custom treatment plan based on the infant's specific problems. The baby may need to receive emergency surgical procedures to repair congenital heart, lung, kidney, or gastrointestinal tract disorders. He or she is often fitted with breathing and feeding tubes and kept in the hospital for several months for careful monitoring.

A baby who survives the first few months of life may be able to go home with the parents. He or she will need to receive regular checkups throughout childhood and take daily medications to avoid potentially fatal complications. Very few people with the disorder survive past adolescence, and those who do reach adulthood are severely mentally and physically handicapped, requiring constant attention and assistance with daily activities.