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The extra chromosome is lethal for most babies born with this condition and it causes major physical abnormalities and severe mental retardation. Very few children afflicted with this disease survive beyond a year. Although we do not know how many babies die we could say it is a problem we should know about.
There are 23 pairs of human chromosomes, and in Trisomy 18 or Edwards syndrome, there is an extra chromosome with the 18th pair. Like Trisomy 21 known as Down syndrome, Trisomy 18 affects all systems of the body and causes distinct facial features. It is estimated to occur in 1 in 6,000-8,000 live births, where unfortunately, about 95% of fetuses die before birth. Therefore, the actual incidence of the disorder may be higher. Of those born, approximately 80% are females although Trisomy 18 affects individuals of all ethnic backgrounds and both sexes. Humans normally have 23 pairs of chromosomes and these chromosomes are numbered 1-22. The 23rd pair is composed of the sex chromosomes, X and Y. A person inherits one set of 23 chromosomes from each parent, so occasionally, a genetic error occurs during egg or sperm cell formation. A child conceived with such an egg or sperm cell may inherit an incorrect number of chromosomes.
As you already heard, in the case of Edwards' syndrome, the child inherits three, rather than two, copies of chromosome 18. Trisomy 18 occurs in approximately one in every 3,000 newborns and affects girls more often than boys, where women older than their early thirties have a greater risk of conceiving a child with Trisomy 18, but it can occur in younger women.
Symptoms of Trisomy 18
A third copy of chromosome 18 causes numerous abnormalities, where most children born with Edwards' syndrome appear weak and fragile, often underweight. The head is unusually small and the back of the head is prominent, the ears are malformed and low-set, and the mouth and jaw are small. The baby may also have a cleft lip or cleft palate, and frequently, the hands are clenched into fists, and the index finger overlaps the other fingers. The child may have clubfeet and toes may be webbed or fused as well. Numerous problems involving the internal organs may be present with abnormalities often occurring in the lungs and diaphragm, and heart defects and blood vessel malformations are common. The child may also have malformed kidneys and abnormalities of the urogenital system as well.
Trisomy 18 severely affects all organ systems of the body, so the symptoms could be various. Symptoms may include different body systems, and are typical for each system.
- Nervous system and brain: mental retardation and delayed development 100% of individuals, high muscle tone, seizures, and physical malformations such as brain defects.
- Head and face: small head (microcephaly), small eyes, wide-set eyes, epicanthal folds, small lower jaw.
- Heart: congenital heart defects at 90% of individuals, such as ventricular septal defect and valve defects.
- Bones: severe growth retardation, clenched hands with 2nd and 5th fingers on top of the others, and other defects of the hands and feet.
- Malformations of the digestive tract, the urinary tract, and genitals of these patients is common as well.
Physical abnormalities point to Edwards' syndrome, but a definitive diagnosis relies on karyotyping, which involves drawing the baby’s blood or bone marrow for a microscopic examination of the chromosomes. Using special stains and microscopy, individual chromosomes are identified. It is valuable that the presence of an extra chromosome 18 could be revealed. It is very good what Trisomy 18 can be detected before birth. If a pregnant woman is older than 35, has a family history of genetic abnormalities, has previously conceived a child with a genetic abnormality, or has suffered earlier miscarriages, she may undergo tests. It is important to determine whether her child carries genetic abnormalities. Potential tests include maternal serum analysis or screening, ultrasonography, amniocentesis, and chorionic villus sampling, depending on the woman’s and her doctor’s decision.
Treatment for Trisomy 18
Unfortunately, there is no cure for Edwards’ syndrome. Since Trisomy 18 babies frequently have major physical abnormalities, doctors and parents face difficult choices regarding treatment. Abnormalities can be treated to a certain degree with surgery, but extreme invasive procedures may not be in the best interests of an infant, since an infants’ lifespan is commonly measured in days or weeks. Medical therapy often consists of supportive care with the goal of making the infant comfortable, rather than prolonging their life. That is why we say that medical care for individuals with Trisomy 18 is supportive.
The treatment focuses on providing nutrition, treating infections, and managing heart problems. During the first months of life, infants with Trisomy 18 require skilled medical care, due to the complex medical problems. Because of heart defects and overwhelming infections, infants have a 5% chance of surviving to the age of one. Advances in medical care over time will, in the future, help more infants with Trisomy 18 live into childhood and beyond of it.
Most children born with Trisomy 18 die within their first year of life, with an average lifespan of under two months for 50% of the children, and 90-95% die before their first birthday. The 5-10% of children who survive their first year are severely mentally retarded and they need support to walk, and their learning is limited as well. Verbal communication is also limited, but they can learn to recognize and interact with other people. It is also important to point out that Edwards’ syndrome or Trisomy 18 cannot be prevented.