Trisomy 18 is also known as Edwards’s syndrome which is marked by the presence of one extra chromosome 18. It causes severe physical abnormalities along with intellectual problems. Children affected with trisomy have very short life and most of them do not live beyond first year. This disorder is marked by abnormal low birth weight with small head (abnormally shaped) and severe defects in heart and other vital organs. One child out of every 6000 births is affected with Trisomy 18.
Normally every child carries two copies of chromosome in every set and in trisomy they have an additional copy of chromosome thus contributing for third chromosome. Presence of 3 chromosomes in the same 18th pair is called Trisomy 18 and only 10% of the affected children live beyond first year.
Though Trisomy 18 is a genetic disorder it is not inherited from parents. It occurs during the fusion of egg and sperm cells or during the early developmental stage of embryo. Some cases will have no extra chromosome but a small portion of chromosome 18 will get attached to another pair thus forming additional material of chromosome. In most of the cases this extra chromosome affects every cell of the body and accordingly the symptoms and severity of the disorder varies with that of the volume of chromosome material present in 18th chromosome.
Exact reason of trisomy 18 is unknown.
The infant affected with trisomy 18 will have low birth weight, small head with abnormal shape, small jaw and overlapping fingers. It will have low set ears, clenched fists, and defects in heart and other organs. Right from birth the child will have feeding problems, respiratory disorders, delayed growth and other complications. Apart from many physical abnormalities the child will also suffer from intellectual problems.
Some other physical complications present in many infants with Trisomy 18 are:-
• Cleft palate
• Deformity in the feet described as rocker bottom feet
• Clenched fists and overlapped fingers. The child cannot straighten the fingers.
• Defective lungs, kidneys and intestine.
• Increased heart defects like atrial septal defect ASD or Ventricular septal defect VSD and valve leakage
• Deformity in the chest
• Delayed growth with intense developmental delay
• Small head with abnormal shape
• Low set ears and small jaw
Who are at risk?
Girls are more prone to develop Trisomy 18 disorder than boys. It is reported that about 80% of affected children are girls.
Tests and Diagnoses :
An expert doctor can detect Trisomy 18 through prenatal testing methods. Chromosome analysis is the right option for diagnosing this disorder. The doctor will measure the Alpha fetoprotein levels through screening tests which is done anywhere from 15th-17th week of pregnancy.
Ultrasound scanning is done for testing the fetus with Trisomy 18. The doctor will look for specific symptoms of abnormalities in the growing fetus. The chromosome material of the fetus can be taken via amniotic fluid. A small needle is inserted into the abdominal wall to collect the abdominal fluid.
No treatment is available for Trisomy 18 since it is a genetic disorder. The condition can never be cured and life expectancy of affected child is too low. With the given set of complications the child cannot survive for more than a year. Treatment can be given by way of providing additional nutrition, prevention of infections, administering diuretic medications for managing heart failure. Very often the child affected with Trisomy 18 will die due to pneumonia or heart failure.