Trisomy 18 Health Article

Definition

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.

Alternative Names

Edwards syndrome

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