The 13th chromosome contains blueprints that direct a baby’s development in the early weeks following conception. When a child has an extra 13th chromosome (three copies, instead of two), as is the case in trisomy 13, the genetic messages are confused and contradictory. This results in multiple significant defects in major organ systems.
The brain is often the most severely affected. Most children with trisomy 13 also have some kind of heart defect. It’s not unusual for these children to be born blind, deaf, and with no sense of smell. Children with trisomy 13 may also have abnormalities in the shape of their lips, eyes, ears, fingers, toes, and bones.
Trisomy 13 was first described in 1657, but four hundred fifty years of medical knowledge have not improved the outlook for children born with this syndrome.
Most babies who are conceived with trisomy 13 die early in gestation. Of the babies who live to be born, about 44 % die within the first month and 69% die by six months. Only 18 percent reach their first birthdays — and these children tend to have severe mental defects and seizures (Smith’s Recognizable Patterns of Human Malformation, Saunders 1988).
A blood test, called the AFP (alphafetoprotein) or triple screen, may help a pregnant woman find out her baby’s risk of several diseases, including Trisomy 21 (Down Syndrome) and Trisomy 13, though it can not give a definite answer.
Trisomy 13 is often detectable on ultrasound as early as 10 weeks. Chorionic villous sampling can detect trisomy 13 by 12 weeks. Amniocentesis, usually performed after 16 weeks gestation, can give a definite answer if any question still remains.
Often trisomy 13 is associated with older mothers. Even so, the risk of having another baby with trisomy 13 is usually very low.
A trisomy 13 translocation is not associated with mom’s age, but is a hereditary chromosome problem. The risk of recurrence in some types of (balanced) translocations can be quite high.
Last reviewed: February 03, 2008