Trisomy 18 is a genetic disorder in which a person has a third copy of genetic material from chromosome 18, instead of the usual two copies.
Causes, incidence, and risk factors
Trisomy 18 is a relatively common syndrome. It is three times more common in girls than boys. The syndrome is caused by the presence of extra material from chromosome 18. The extra material interferes with normal development.
Signs and tests
Examination of the pregnant woman may show an unusually large uterus and extra amniotic fluid. An unusually small placenta may be seen when the baby is born.
Other signs include:
- Hole, split, or cleft in the iris (coloboma)
- Separation between the left and right side of the rectus abdominis muscle (diastasis recti)
- Umbilical hernia or inguinal hernia
There are often signs of congenital heart disease, such as:
Tests may also show kidney problems, including:
Treatment of children with Trisomy 18 is planned on a case-by-case basis. Which treatments are used depends on the patient's individual condition.
Fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to the teenage years, but with serious medical and developmental problems.
Complications depend on the specific defects and symptoms.
Calling your health care provider
Call your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child. Genetic counseling can help families understand the condition, the risks of inheriting it, and how to care for the patient.
Prenatal diagnosis of trisomy 18 is possible with an amniocentesis or chorionic villus sampling and chromosome studies on amniotic cells. Parents who have a child with translocational Trisomy 18 and want additional children should have chromosome studies, because they are at increased risk of having another child with Trisomy 18.
Reviewed By: Diana Chambers, MS, EdD, Certified Genetics Counselor (ABMG), Charter Member of the ABGC, University of Tennessee, Memphis, TN. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.