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What is trisomy 18?
Trisomy 18, also known as Edwards syndrome, is the second most common trisomy behind trisomy 21 (Down syndrome). It occurs in 1 in 5,000 live births and it is caused by the presence of an extra chromosome 18 and similar to Down syndrome. It is seen more commonly with increasing maternal age. Babies born with trisomy 18 have distinct clinical features, including developmental delay and craniofacial, limb, heart, and kidney abnormalities. Half of all babies born with Edwards syndrome die within the first week, and only 5% to 10% live beyond the first year of life.
What causes trisomy 18? What are the different kinds of trisomy 18?
A trisomy is caused by a genetic error in which three copies of a chromosome (instead of two) are inherited from the parents. Trisomy 18 is caused by the presence of an extra chromosome 18, and most frequently is of maternal origin and includes the entire chromosome in most cases (>90%) rather than a part of the chromosome (also known as partial trisomy or incomplete trisomy). In a small percentage of patients, an additional chromosome 18 is present in some, but not all cells, and is referred to as a mosaicism; these affected patients may not present with the typical features of Edwards syndrome listed below.
What are the signs and symptoms of trisomy 18?
Today the majority of fetuses with trisomy 18 are diagnosed prior to birth and research indicates that many of these fetuses do not survive to birth. For those infants who do survive, they are at risk for any number of abnormalities, but the typical features include:
- intrauterine growth retardation
- craniofacial features such as abnormalities of the jaw, skull, ears, and neck
- clenched fists with overriding fingers
- small fingernails
- short sternum
- club feet
- heart defects
- kidney defects
- neurodevelopmental delays
How is trisomy 18 diagnosed?
Most cases of trisomy 18 are diagnosed prenatally. Standard pregnancy screening during the first and second trimesters including serum markers (plasma protein, beta-hCG, alpha-fetoprotein, unconjugated estriol, and inhibin A) with ultrasound (nuchal translucency and other anatomic abnormalities) can accurately diagnose more than three quarters of all cases. Chorionic villi sampling (CVS) is another genetic-based test that can diagnose trisomy 18. This diagnosis of trisomy 18 is important in order to better prepare parents and caregivers due to the high risk of fetal demise and early postnatal death. There are a number of support groups available to families dealing with these types of issues.
What is the treatment for trisomy 18?
The treatment and management of children with Edwards syndrome is dependent upon the severity of findings. There is no definitive treatment for children with trisomy 18, and there are ethical issues surrounding the management of these newborns due to the high mortality rate and difficulty in predicting which infants will live beyond their first year of life. The major cause of death in many of these infants is sudden death due to neurological instability, cardiac failure, and respiratory failure. For those infants diagnosed with incomplete trisomy 18 or mosaic trisomy 18, management is focused on addressing abnormalities present since they have such a variable prognosis.
What is the life expectancy for someone with trisomy 18?
The average lifespan for infants born with trisomy 18 is 3 days to 2 weeks. Studies show that 60% to 75% of children survive for 24 hours, 20% to 60% for 1 week, 22% to 44% for 1 month, 9% to 18% for 6 months, and 5% to 10% for over 1 year. Therefore, there are quite a few affected children who require significant care and ongoing screening during their lives. Specialists in pediatric development, neurology, and genetics are often helpful with guiding the ongoing care of these children. There are great support groups such as the Support Organization for Trisomy 18, 13 and Related Disorders (SOFT) and the Trisomy 18 Foundation for parents and providers seeking guidance. In addition there is an increasing approach to management which is moving away from pure palliative care into optimizing quality of life. This is due to the increasing evidence that a collaborative model of decision making involving parents and providers is a better way to approach the child with Edwards syndrome.
Health Solutions From Our Sponsors
Carey, J. C. "Perspectives on the care and management of infants with trisomy 18 and trisomy 13: striving for balance." Current Opinion in Pediatrics 24.6 (2012): 672-678.
Cereda, A. and J. C. Carey. "The trisomy 18 syndrome." Orphanet Journal of Rare Diseases 7.81 (2012).
Lorenz, J. M. and G. E. Hardart. "Evolving medical and surgical management of infants with trisomy 18." Current Opinion in Pediatrics 26.2 (2014): 169-176.
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Top Trisomy 18 (Edwards Syndrome) Related Articles
Chorionic Villus SamplingThis prenatal test involves taking a small sample of cells from the placenta to check for birth defects, genetic diseases, and other problems. Candidates for the test include pregnant women age 35 years or older, couples who have had a child with a birth defect, and pregnant woman who have had other abnormal genetic test results. Potential risks of the test include miscarriage and infection. Cells may be collected through the vagina or through the abdomen.
Down Syndrome OverviewGet the facts on Down syndrome, a genetic disorder caused by an additional set of chromosomes in a developing fetus. Down syndrome signs and symptoms include:
- distinctive facial features,
- growth retardation, and
- decreased mental function and IQ.
Genetic DiseaseThe definition of a genetic disease is a disorder or condition caused by abnormalities in a person's genome. Some types of genetic inheritance include single inheritance, including cystic fibrosis, sickle cell anemia, Marfan syndrome, and hemochromatosis. Other types of genetic diseases include multifactorial inheritance. Still other types of genetic diseases include chromosome abnormalities (for example, Turner syndrome, and Klinefelter syndrome), and mitochondrial inheritance (for example, epilepsy and dementia).
PregnancySigns and symptoms of pregnancy vary by stage (trimester). The earliest pregnancy symptom is typically a missed period, but others include breast swelling and tenderness, nausea and sometimes vomiting, fatigue, and bloating. Second trimester symptoms include backache, weight gain, itching, and possible stretch marks. Third trimester symptoms are additional weight gain, heartburn, hemorrhoids, swelling of the ankles, fingers, and face, breast tenderness, and trouble sleeping. Eating a healthy diet, getting a moderate amount of exercise, also are recommended for a healthy pregnancy. Information about the week by week growth of your baby in the womb are provided.
Prenatal UltrasoundA prenatal ultrasound test uses high-frequency sound waves, inaudible to the human ear, that are transmitted through the abdomen via a device called a transducer to look at the inside of the abdomen. With prenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby. An ultrasound examination is also known as a sonogram.