Edwards syndrome, also known as trisomy 18, is a genetic disorder that arises due to erroneous triplication of chromosome 18. The disorder usually leads to severe malformations of organs, which interfere with the normal functions of the body. Babies with Edwards syndrome may begin to display signs and symptoms right from the fetal stage, and the signs of the disorder are visible right after birth in most cases.
Read on to learn about the causes, symptoms, treatment, and prevention of Edwards syndrome in babies.
What Is Edwards Syndrome?
The nucleus (central component) of each healthy cell of the body has 23 pairs of chromosomes (46 chromosomes per cell), which are thread-like structures containing DNA, the life’s basic molecule. A baby born with Edwards syndrome has an extra chromosome 18 instead of a pair. This genetic error or disorder is called trisomy 18 since there are three copies of chromosome 18 instead of the usual two copies (1).
Trisomy 18 was first described by the geneticist John Hilton Edwards; thus, it is also called Edwards syndrome (2). There are different types of Edwards syndrome.
Types Of Edwards Syndrome
There are three types of trisomy 18 depending on the extent of error and triplication of chromosome 18 (3).
- Full trisomy 18: An extra third chromosome 18 is present in all cells of the body.
- Mosaic trisomy 18: An extra third chromosome 18 is present only in a few cells of the body. This is usually a rare form of Edwards syndrome.
- Partial trisomy 18: Only a part of the extra chromosome 18 is present in each cell. In such cases, the extra bit of chromosome 18 is often attached to another chromosome in the cell — a condition called translocation. In some cases of translocation, a section of chromosome 18 is attached to another chromosome while the three copies of chromosome 18 persist
How Common Is Edwards Syndrome?
According to the Trisomy 18 Foundation, Edwards syndrome occurs in one out of 2,500 pregnancies and one out of 6,000 live births in the United States (4). The disorder has a high fetal mortality rate, and 50% of pregnancies with a trisomy 18 fetus usually lead to stillbirth. Female fetuses are more likely to survive up to term than male fetuses.
The survival rate of live births beyond the first week is 50% (3). About 10% of babies with trisomy 18 survive beyond their first birthday. The risk of having a second child with trisomy 18 is usually less than 1%, and the risk tends to increase with maternal age (5). Maternal age may become a significant risk factor when the mother is older than 35 years.
Causes Of Edwards Syndrome
- Genetic mutations during fertilization: An egg (female gamete) and sperm (male gamete) have 23 chromosomes each. During fertilization, they fuse to form a zygote, a precursor cell to the fetus. The zygote assimilates 23 chromosomes from each gamete to carry 46 chromosomes or 23 pairs. Sometimes, there could be an error during the formation of the zygote, causing it to develop an extra chromosome 18 instead of two, leading to trisomy 18.
- Genetic mutations in the embryonic stage: The embryo is the stage after the zygote. The zygote may begin development with a pair of chromosome 18. However, at some point during cell division in the embryonic stage, chromosome 18 may triplicate. Genetic mutations in the embryonic stage usually lead to mosaic trisomy 18, where only some cells of the body possess three copies of chromosome 18.
- Genetic mutations in the gametes: Genetic errors during the formation of an egg or a sperm could make it possess a pair of 18th chromosomes instead of one, causing the sperm or egg to have 24 chromosomes instead of 23. When a gamete with an extra chromosome 18 fuses with another gamete, the resultant zygote receives three copies of chromosome 18.
- Translocation: Sometimes, in a gamete (egg or sperm), a part or entire chromosome 18 is attached to another chromosome. This condition is called translocation. It may happen when the parent already has partial trisomy 18 or has the genetic material of chromosome 18 intermingled with another chromosome. Translocation could cause the baby to develop partial trisomy 18. Translocation is the only way a baby can inherit Edwards syndrome since other causes are random genetic mutations.
Symptoms Of Edwards Syndrome
The signs and symptoms of Edwards syndrome vary depending on the type of trisomy 18 and its effects on the baby. The following are the most notable signs and symptoms of Edwards syndrome (9) (10) (11).
- Heart defects, such as ventricular septal defects (hole in the heart); 90% of babies with trisomy 18 have heart defects
- Cleft lip and palate
- Hand and foot abnormalities
- Breathing difficulties
- Problems in regulating body temperature
- Feeding difficulties
- Small size and frail body
- Severe psychomotor and growth retardation
- Microcephaly (smaller head size) but with a prominent forehead
- Smaller eyes, mouth, ears, and jaws
- Clenched fingers
- Kidney problems, such as polycystic kidney disease
- Defective and deformed internal organs
- Dislocated esophagus
- Low birth weight
- Low muscle tone
- High blood pressure
- Scoliosis (abnormal spine curvature)
- Undescended testicles in boys
- Umbilical or inguinal hernia
- Impaired vision
- Webbed neck
- Signs of hepatoblastoma (a type of liver cancer) and Wilms tumor (a type of kidney cancer)
- Spina bifida (spinal cord defect)
Diagnosis Of Edwards Syndrome
The diagnosis of Edwards syndrome can be made through prenatal tests (before the baby’s birth) or postnatal tests (after the baby’s birth). The following methods could be used for diagnosis (12).
- Ultrasonography: Routine ultrasound during pregnancy could help detect fetal physical anomalies that indicate trisomy 18.
- Maternal serum screening: If the physician suspects a defect due to chromosomal abnormalities, they may recommend a blood test to determine the presence of certain markers in the mother’s blood serum. These markers could indicate a potential risk of chromosomal abnormalities in the baby.
- Amniocentesis and chorionic villus sampling: If blood tests turn out positive, the doctor may recommend amniocentesis, a test where a small sample of the amniotic fluid is collected to analyze genetic anomalies. Chorionic villus sampling is a test that involves collecting a small sample of the placenta to test for the presence of any genetic abnormalities.
- Physical evaluation: Most doctors can diagnose Edwards syndrome during the routine post-birth physical evaluation of the baby. Physical anomalies such as frail body and clenched fingers could immediately suggest trisomy 18.
- Medical imaging tests: A doctor may use imaging tests, such as MRI and X-ray, to visualize bones and organs of the body and check for signs of Edwards syndrome. These tests could be especially helpful in cases of partial trisomy 18, where the physical signs of the condition tend to be less severe.
- Chromosome analysis: If the baby presents physical problems and imaging tests show anomalies, a chromosome analysis could be conducted. A blood sample is collected and checked for the presence of three copies of chromosome 18.
If a physician suspects the presence of chromosomal abnormalities during an ultrasound, a test might be conducted in each trimester to confirm genetic anomalies and their prognosis.
A doctor may refer the parents to a genetic physician and genetic counselor, who can explain the results of the chromosomal tests in detail. It also includes explaining the prognosis of the condition in the baby and the risk of recurrence in future pregnancies.
Treatment Of Edwards Syndrome
There is no cure for trisomy 18, and there is no conclusive data to prove that the condition can be prevented before conception or during pregnancy (9).
The treatment for Edwards syndrome consists of symptomatic and supportive care, depending on the affected parts or organs of the body and the severity of the disorder. In most cases, the care requires a coordinated effort of a multidisciplinary team of medical professionals who focus on (12):
- Early intervention
- Occupational therapy
- Parental education about home nursing care
The following supportive treatments are usually considered to manage Edwards syndrome in babies (12).
- Provision of essential nutrients through feeding tubes
- Oxygen therapy to ensure sufficient oxygen supply to the lungs and blood
- Placement of a tracheostomy tube
- Surgical correction of physical abnormalities
- Cardiac surgery to correct heart defects
- Chemotherapy for babies with cancerous lesions
- Speech therapy
Parents may need to make difficult decisions during pregnancy or supportive care based on the probable survival rate of the fetus or the baby. You may extensively discuss the outcomes with a genetic counselor. There are several foundations and organizations that may provide you resources or support necessary to make a decision that is in the best interest of you and your baby.
Edwards syndrome is a genetic disorder with no known cure and prevention method. Early intervention and care are the best ways to ensure favorable outcomes. Thanks to the advancements in medical technology, babies with heart defects could show a positive prognosis. A baby with trisomy 18 will require long-term care through childhood and adulthood. Speak to a specialist to determine the appropriate long-term supportive care for your baby.
2. Mark Zhang, Trisomy 18 (Edwards Syndrome); The Embryo Project Encyclopedia
3. Trisomy 18; Mount Sinai Health System
4. What Is Trisomy 18?; Trisomy 18 Foundation
5. Trisomy 18; The Chromosome 18 Registry & Research Society
6. Trisomy 13 and Trisomy 18 in Children; Stanford’s Children Health
7. Trisomy 18 and 13; Boston Children’s Hospital
8. Trisomy 18; National Cancer Institute
9. Trisomy 18 and 13; Children’s Wisconsin
10. Trisomy 13 and Trisomy 18 in Children; University of Rochester
11. Dr Daniel J Bell et al., Edwards syndrome; Radiopaedia
12. Trisomy 18; National Organization of Rare Disorders