Trisomy 18 (Edwards Syndrome)

Trisomy 18 or Edwards syndrome is a genetic disorder that causes a raft of life-threatening birth defects. Only a small minority of infants born with Edwards syndrome live more than a year.

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.

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.

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

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.

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.

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.