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.
- Mental retardation, severe
- 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)
- 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 X-Rays or ultrasound may reveal abnormal rotation of the internal organs.
MRI or CT scans of the head may reveal a structural abnormality of the brain, called holoprosencephaly, where the 2 cerebral hemispheres are fused.
Chromosome studies show trisomy 13, partial trisomy, trisomy 13 mosaic, or translocation.
Because of the severity of congenital defects, life-sustaining procedures are generally not attempted.
Support Organization for Trisomy 18, 13 and Related Disorders (SOFT)
2982 S. Union St.
Rochester, NY 14624
Extremely short survival time is expected - 80% of babies die in the first month of life. Survivors have severe mental defects. Rarely, affected persons survive to adulthood.
Complications begin almost immediately. They include breathing difficulty or lack of breathing (apnea), deafness, vision problems, feeding problems, seizures, heart failure, and others.
Calling your health care provider
Call for an appointment with your health care provider if you have had a child with Trisomy 13, and you plan to have another child.
Trisomy 13 can be diagnosed prenatally by amniocentesis with chromosome studies of the amniotic cells. Trisomy 13 mosaicism and partial trisomy 13 also occur. Parents of infants with translocation type trisomy 13 should also have translocation studies.
by Armen E. Martirosyan, M.D.