Trisomy 18 is a genetic disorder in which a person has a third copy of material from chromosome 18, instead of the usual 2 copies.
Trisomy 18 occurs in 1 in 6,000 live births. It is 3 times more common in girls than boys.
The syndrome occurs when there is extra material from chromosome 18. The extra material affects normal development.
Symptoms may include:
An exam during pregnancy may show an unusually large uterus and extra amniotic fluid. There may be an unusually small placenta when the baby is born. A physical exam of the infant may show unusual fingerprint patterns. X-rays may show a short breast bone.
Chromosome studies will show trisomy 18. The chromosome abnormality may be present in every cell or present in only a certain percentage of the cells (called mosaicism). Studies may also show part of the chromosome in some cells. Rarely, part of the chromosome 18 becomes attached to another chromosome. This is called translocation.
Other signs include:
There are often signs of congenital heart disease, such as:
Tests may also show kidney problems, including:
There are no specific treatments for trisomy 18. Which treatments are used depend on the person's individual condition.
Support groups include:
Half of infants with this condition do not survive beyond the first week of life. Nine out of ten children will die by 1 year of age. Some children have survived to the teenage years, but with serious medical and developmental problems.
Complications depend on the specific defects and symptoms.
Genetic counseling can help families understand the condition, the risks of inheriting it, and how to care for the person.
Tests can be done during pregnancy to find out if the child has this syndrome.
Genetic counseling is recommended for parents who have a child with this syndrome and who want to have more children.
Reviewed By: Anna C. Edens Hurst, MD, MS, Assistant Professor in Medical Genetics, The University of Alabama at Birmingham, Birmingham, AL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.