Trisomy 18

Trisomy 18 is a genetic disorder associated with the presence of extra material from chromosome 18.

Trisomy 18 is a relatively common syndrome affecting approximately 1 out of 3,000 live births. It is three times more common in girls than boys. The syndrome is caused by the presence of an extra material from chromosome 18. The extra material interferes with normal development.

• Clenched hands
• Crossed legs (preferred position)
• Heart disease (congenital)
• Hole, split, or cleft in the iris (coloboma)
• Kidney problems
• Low birth weight
• Low-set ears
• Mental deficiency
• Separation between the left and right side of the rectus abdominis muscle (diastasis recti)
• Small head (microcephaly)
• Small jaw (micrognathia)
• Umbilical hernia or inguinal hernia
• Underdeveloped fingernails
• Undescended testicle
• Unusual shaped chest (Pectus carinatum)

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 finger print patterns. X-rays may show a short breast bone. Chromosome studies show trisomy 18, partial trisomy, or translocation.

There are often signs of congenital heart disease, such as:

• VSD (ventricular septal defect)
• ASD (atrial septal defect)
• PDA (patent ductus arteriosus)

Tests may also show kidney problems, including:

• Horseshoe kidney
• Hydronephrosis
• Polycystic kidney

Medical management of children with Trisomy 18 is planned on a case-by-case basis and depends on the individual circumstances of the patient.

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

Fifty percent of infants with this condition do not survive beyond the first week of life. Some children have survived to teenage years, but with serious medical and developmental problems.

Complications depend on the specific defects and symptoms.

Call your health care provider and genetic counselor if you have had a child with Trisomy 18 and you plan to have another child.

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 to have another child with trisomy 18.