Trisomy 13

Alternative names

Patau syndrome

Definition

Trisomy 13 is a syndrome associated with the presence of a third (extra) number 13 chromosome.

Causes, incidence, and risk factors

Trisomy 13 occurs in about 1 out of every 5,000 live births. It is a syndrome with multiple abnormalities, many of which are not compatible with more than a few months of life. Almost half of the affected infants do not survive beyond the first month, and about three quarters die within 6 months.

Trisomy 13 is associated with multiple abnormalities, including severe mental defects and defects of the brain that lead to seizures (hypsarrhythmia), apnea, deafness, and ocular (relating to the eye) abnormalities.

The eyes are small with defects in the iris (coloboma). Most infants have a cleft lip and cleft palate, and low-set ears. Congenital heart disease is present in approximately 80% of affected infants. Hernias and genital abnormalities are common.

Symptoms

• Mental retardation, severe
  
• Seizures
  
• Small head (microcephaly)
  
• Scalp defects (absent skin)
  
• Small eyes (microphthalmia)
  
• Cleft lip and/or palate
  
• Eyes close set (hypotelorism) - eyes may actually fuse together into one
  
• Iris defects (coloboma)
  
• Pinna abnormalities and low set ears
  
• Simian crease
  
• Extra digits (polydactyly)
  
• Hernias: umbilical hernia, inguinal hernia
  
• Undescended testicle (cryptorchidism)
  
• Hypotonia
  
• Micrognathia
  
• Motormental retardation
  
• Skeletal (limb) abnormalities
  

Signs and tests
The infant may have a single umbilical artery at birth. There are often signs of congenital heart disease:

• Ventricular septal defect (VSD)
  
• Atrial septal defect (ASD)
  
• Patent ductus arteriosus (PDA)
  
• Abnormal placement of the heart (dextroversion - the heart is placed toward the right side of the chest instead of the left)
  

Gastrointestinal or ultrasound may reveal abnormal rotation of the internal organs.