Trisomy 18 is better known as Edwards syndrome after the geneticist who described the clinical picture, John Edwards. It is a very serious congenital disease that causes alterations throughout the body and often leads to death before the baby reaches the first year of life.

In this article we will look at what the causes and symptoms of this condition are and what the three subtypes of Edwards syndrome are, which differ in the way trisomy occurs.

What is Edwards syndrome?

Edwards syndrome is a disease caused by genetic failure ; specifically, it results from a trisomy, or duplication, of chromosome 18. This is why it is also known as “trisomy 18”.

This alteration causes the baby’s body not to develop properly, so that multiple physical defects occur and increases the risk of premature death : only 7.5% of babies diagnosed live longer than a year.

It is a very common disease that affects 1 in 5 thousand newborns, most of them female. In fact, it is the most common trisomy after Down syndrome, in which chromosome 21 is duplicated.

Considering that a large number of miscarriages occur as a result of this alteration, especially in the second and third trimesters, the prevalence rises if we refer to the fetal period rather than the perinatal period.

Symptoms and signs

There are multiple symptoms and signs that denote the presence of Edwards syndrome, although not all occur simultaneously. The most common ones are described below:

  • Malformations in the kidneys.
  • Malformations in the heart : defects in the ventricular and/or atrial septum, patent ductus arteriosus, etc.
  • Difficulties in eating.
  • Esophageal atresia-The esophagus is not connected to the stomach, so nutrients do not reach the stomach.
  • Omphalocele-The intestines protrude from the body through the navel.
  • Breathing difficulties.
  • Arthrogryposis: presence of contractures in the joints, especially in the extremities.
  • Postnatal growth deficiency and developmental delay.
  • Cysts in the choroid plexuses, which produce the spinal fluid; they do not cause problems but are a prenatal sign of Edwards syndrome
  • Microcephaly : insufficient development of the head.
  • Micrognathia: jawbone of less than expected size.
  • Cleft palate (cleft lip).
  • Malformations in the ears, often located lower than usual.
  • Eyes wide apart, small and droopy eyelids (ptosis).
  • Keeled chest or “pigeon breast”: the chest protrudes into the area of the sternum.
  • Abnormally short sternum.
  • Absence of the radius, one of the main bones of the forearm.
  • Closed and tight hands with overlapping fingers.
  • Underdeveloped thumbs and nails.
  • Convex (“rocking”) feet
  • Presence of webbing joining the toes.
  • Cryptorchidism: In males, the testicles do not descend properly.
  • Weak cry.
  • Severe intellectual disability .

Causes of Edwards syndrome

The chance of having a baby with trisomy 18 increases with age, most commonly around age 40. Mothers who have already had a child with this disease have about a 1% chance that the condition will recur in later pregnancies.

Edwards syndrome is caused by a trisomy of the 18th chromosome . This means that affected babies have three copies of this chromosome, when they normally have two pairs of each of the 23.

Trisomy is usually caused by chromosome duplication in the egg or sperm ; when the two reproductive cells join to form the zygote, it develops by dividing successively, and the genetic defect is repeated at each division. At other times, trisomy occurs during early fetal development.

Although the most common cause of Edwards syndrome is the duplication of chromosome 18, this disease may also be due to other genetic errors, such as translocation. These differences result in the different types of trisomy 18.

Types of trisomy 18

There are three types of Edwards syndrome based on the characteristics of chromosome 18 trisomy. The severity of the baby’s symptoms may vary depending on the type of trisomy.

1. Complete or classic trisomy

This is the most common form of Edwards syndrome. In classical trisomy, all the cells in the body have three complete copies of chromosome 18.

Because the involvement is so widespread, in cases of complete trisomy the symptoms are usually more severe than in other types of Edwards syndrome.

2. Partial trisomy

Partial trisomy 18 is an uncommon type of Edwards syndrome caused by incomplete duplication of the chromosome. These cases are usually due to translocation, that is, the breaking of chromosome 18 and the attachment of the separated part to a different chromosome.

The severity and specific symptoms of each case of partial trisomy vary greatly because the duplications can affect different segments of the chromosome, but the changes are usually less severe than the classic syndrome.

3. Mosaic trisomy

This type of trisomy occurs when the extra chromosome 18 is not found in every cell in the baby’s body , but some have 2 copies and others have 3.

People affected by mosaic trisomy may show severe or mild symptoms or no physical alteration; however, the risk of premature death remains very high.

Prognosis and treatment

Today, Edwards syndrome is usually detected before birth by amniocentesis, a test that involves analyzing the amniotic fluid (which protects the baby and allows it to obtain nutrients) to determine possible chromosomal abnormalities and fetal infections, as well as the baby’s sex.

Less than 10% of trisomy 18 fetuses are born alive. Of these, 90% die during the first year of life , half of them during the first week. The average life expectancy for babies with Edwards syndrome is between 5 days and 2 weeks. Death usually occurs from cardiac and respiratory disorders.

Edwards syndrome has no cure, so treatment aims to increase the quality of life of the affected person as much as possible. Less severe cases of trisomy 18 do not always result in death in childhood, but they often cause major health problems and few patients live beyond 20 or 30 years.