Trisomy 18
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Nature of the Genetic Difficulty

"The karyotype for Edward's Syndrome. Note the three chromosomes in position 18."
Edward’s syndrome, also known as trisomy 18 syndrome, is a disease that occurs when a child inherits an extra copy of chromosome 18. The third chromosome causes extreme mental retardation and major physical abnormalities. It is highly Trisomy18bryannick.gifunlikely for children afflicted to survive more than a year because the extra chromosome is lethal to most babies. The extra chromosome is caused before conception when a genetic fault occurs during meiosis, the formation and production of sperm and egg. The afflicted child would then have inherited one such sperm or egg for Edward’s syndrome to occur and be expressed in the offspring. Edwards’ Syndrome was first recognized in 1960 by the discovery of an extra chromosome 18 in babies. It is named after John H. Edwards

Basic Facts of Disease

  • 80% of cases are female
  • Severely damages and affects all organ systems of the body
  • Occurs approximately once in every 6,000-8,000 live births
  • However, 1 in every 400 feti at the first trimester mark are diagnosed.
  • 95% of cases cause death before birth (miscarriage)
  • 5-10% of affected live births survive through their first year of live
  • Trisomy 18 has no racial tendencies
  • The high mortality rate is caused mainly by severe cardiac and renal malformations, as well as feeding difficulties and apnea.


Symptoms can be noticed as soon as the afflicted child is born. The newborns are normally underweight and appear to be weak and frail. A few physical abnormalities include:
  • the head and mouth being unusually small
  • the index finger on the child’s hand overlapping the other fingers
  • the child’s feet being webbed or merged together.
Many deformities may be internal. The child may have trouble breathing because of problems in the lungs and diaphragm. Heart defects and malformations of the blood vessels are also common. Lastly the child’s kidneys may be deformed and the child may have trouble urinating.
Because Edwards’ syndrome is cause by a genetic fault before conception, there is no cure and cannot be prevented. While some treatment is available, most of it is just to make the child comfortable before his inevitable, pre-mature death. Certain abnormalities can be treated with surgery but it will not prolong the child’s life.
The few children who survive will live severely handicapped.For the few that survive their first year, support is needed for the child to walk. Learning and verbal communication is limited. The child can learn to interact and recognize others. Fortunately,they will also retain a degree of brain activity that allows for laughter and interaction with others.

Sources Cited