Definition of Trisomy 18:

Trisomy 18 is a genetic disorder in which a person has a third copy of 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.

Symptoms:

• Clenched hands
• Crossed legs (preferred position)
• Feet with a rounded bottom (rocker-bottom feet)
• Low birth weight
• Low-set ears
• Mental deficiency
• Small head (microcephaly)
• Small jaw (micrognathia)
• Underdeveloped fingernails
• Undescended testicle
• Unusual shaped chest (pectus carinatum)

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.

Physical examination of the infant may show unusual fingerprint patterns. X-rays may show a short breast bone. Chromosome studies show trisomy 18, partial trisomy, or translocation.

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:

• Atrial septal defect (ASD)
• Patent ductus arteriosus (PDA)
• Ventricular septal defect (VSD)

Tests may also show kidney problems, including:

• Horseshoe kidney
• Hydronephrosis
• Polycystic kidney

Treatment:

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.

Support Groups:

• Support Organization for Trisomy 18, 13 and Related Disorders (SOFT) - www.trisomy.org
• Trisomy 18 Foundation - www.trisomy18.org

Expectations (prognosis):

Half 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:

Complications depend on the specific defects and symptoms.

Calling your health care provider:

Genetic counseling can help families understand the condition, the risks of inheriting it, and how to care for the patient.

Prevention:

Tests can be done during pregnancy to determine if the child has this syndrome.

Genetic testing is recommended for parents who have a child with this syndrome who want additional children.