Trisomy 18

Alternative names

Edwards syndrome

Definition

Trisomy 18 is a syndrome associated with the presence of a third (extra) number 18 chromosome.

Causes, incidence, and risk factors

Trisomy 18 is a relatively common syndrome affecting approximately 1 out of 3,000 live births and affecting girls more than three times as often as boys. Multiple abnormalities are associated with the presence of an extra number 18 chromosome. Many of these abnormalities are not compatible with more than a few months of life. Few infants survive beyond the first year.

Common findings include low birth weight, mental retardation, low-set ears, malformed ears, small jaw (micrognathia), hand abnormalities, congenital heart disease, hernias, and undescended testicle (cryptorchidism). There may be many other abnormalities noted.

Symptoms

• Unusually large uterus during pregnancy
  
• Low birth weight infant
  
• Mental deficiency
  
• Low-set ears
  
• Small jaw (micrognathia)
  
• Clenched hands
  
• Hypoplastic (underdeveloped) fingernails
  
• Umbilical hernia or inguinal hernia
  
• Diastasis recti
  
• Cryptorchidism
  
• Crossed legs (preferred position)
  
• Congenital heart disease
  o VSD (ventricular septal defect)
  o ASD (atrial septal defect)
  o PDA (patent ductus arteriosus)
  
• Congenital kidney abnormalities
  o Horseshoe kidney
  o Hydronephrosis
  o Polycystic kidney
  
• Coloboma of iris
  
• Microcephaly
  
• Motormental retardation
  
• Pectus carinatum
  

Signs and tests

Examination of the pregnant woman may show polyhydramnios (extra amniotic fluid). At the birth of the child, an unusually small placenta may be noted.

Physical examination may show an excess of arched type finger print patterns. X-rays may reveal a short breast bone (sternum). Chromosome studies show trisomy 18, partial trisomy, or translocation.

Treatment

Treatment is supportive, but life-sustaining measures are not recommended.