Genetics Northern California

Trisomy 18

What is trisomy 18?
How common is trisomy 18?
What causes trisomy 18?
How is trisomy 18 diagnosed?
Can trisomy 18 be diagnosed during pregnancy?
How is trisomy 18 treated?
Where can I get more information about trisomy 18? 

What is trisomy 18?
Trisomy 18, also called Edwards Syndrome, is a genetic condition that causes birth defects and intellectual disability. Trisomy 18 often results in miscarriage and infant death.

Medical concerns in trisomy 18
Trisomy 18 causes serious medical problems. Newborns with trisomy 18 often struggle to breathe and feed properly, and many live for less than two weeks. Fewer than 1 in 10 babies with this condition live to a year.
Common medical concerns seen in children with trisomy 18 include:
      Breathing problems
      Heart defects
      Kidney defects
      Digestive system defects
      Low muscle tone
      Slow growth

Learning in trisomy 18  
Most children with trisomy 18 have severe to profound intellectual disability. Children can slowly achieve some early milestones, such as smiling and responding to family members. 

How common is trisomy 18?
Trisomy 18 is rare. Less than 1 out of 3000 babies is born with trisomy 18.  

What causes Trisomy 18?
Trisomy 18Trisomy 18 is most often caused by an extra chromosome 18 in all cells of the body. Normally, we have 23 pairs of chromosomes in each cell, which contain our genetic material. This includes two copies of chromosome 18, one from each parent. Most individuals with trisomy 18 have three separate copies of chromosome 18 (instead of the normal two) in every cell of the body. This type of trisomy 18 occurs randomly and does NOT run in families. It is NOT caused by anything a parent did before or during pregnancy. Trisomy 18 becomes more likely as a woman ages, but it can happen in mothers of any age. 

Less often trisomy 18 is caused by mosaicism or a translocation. Mosaicism happens when not every cell has the extra chromosome. A translocation is when the extra chromosome 18 is attached to a different chromosome. These cases have the same medical concerns as the full trisomy. The differences can only be found by looking at the chromosomes in a lab.  Rarely, translocations can be inherited from a parent without trisomy 18. However, in most of these cases, the condition still does NOT run in families. If you have a family history of trisomy 18 you can contact a genetic counselor to determine your chance of having a child with the condition.  
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How is trisomy 18 diagnosed?
Trisomy 18 is accurately diagnosed by studying the baby’s chromosomes through prenatal testing or a blood test after birth. Trisomy 18 may be suspected at birth based on a combination of facial features, heart defects, and other common medical complications. A chromosome study is always done to confirm the diagnosis.  Chromosome testing will also show if other family members may be at higher risk for Trisomy 18.

Can trisomy 18 be diagnosed during pregnancy?
Trisomy 18 can be diagnosed during pregnancy with a diagnostic test, either chorionic villus sampling (CVS) or amniocentesis. These tests look directly at the chromosomes of the developing baby.

Prenatal screening tests can tell you about your risk for trisomy 18, but they do not tell you whether or not the baby has the condition. Screening tests may include a blood test on the pregnant woman or an ultrasound of the developing baby. If these tests show a higher risk for trisomy 18, a woman is offered the option of a diagnostic test to find out if the baby has it for sure.
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How is trisomy 18 treated?
There is no cure for trisomy 18, but medical treatment can address some of the related problems. Surgery can improve comfort and life expectancy in some cases. Most states have programs that help families care for children with special needs. There are also trisomy 18 support groups.

Where can I get more information about trisomy 18?

General information
Medline Plus: Trisomy 18 – General information about trisomy 18 provided by the National Library of Health and the National institute of Health. Extensive links to related online resources.

Parent Support Resources
SOFT: Support Organization for Trisomy 18, 13 and Related Disease – Provides information and support for families with children with trisomy 18.
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Last reviewed: October 14, 2015

Reviewed by: 
      Lauren Gunderson
      Kimberly Barr, MS, LCCG
      Leslie Manace, MD, MPhil