Edwards syndrome (trisomy 18): causes, symptoms and types

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

In this article we will see what they are the causes and symptoms of this disease and what are the three subtypes of Edwards syndrome, which differ in how trisomy occurs.

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What is Edwards syndrome?

Edwards syndrome is a disease caused by genetic failures; specifically, it occurs as a consequence of a trisomy, or duplication, of chromosome 18. This is why it is also known as "trisomy 18".

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

It is a very common disease that affects 1 in 5,000 newborns, most of them female. In fact, it is the most common trisomy after Down syndrome, in which chromosome 21 is duplicated.

Taking into account that a large number of miscarriages They occur as a result of this alteration, especially in the second and third trimesters, the prevalence increases if we refer to the fetal period instead of the perinatal period.

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Symptoms and signs

There are multiple symptoms and signs that indicate the presence of Edwards syndrome, although not all of them occur simultaneously. Below we will describe the most common:

• Malformations in the kidneys.
• Malformations in the heart: defects in the ventricular and / or atrial septum, patent ductus arteriosus, etc.
• Difficulty eating.
• Esophageal atresia: the esophagus is not connected to the stomach, so nutrients do not reach it.
• Omphalocele: The intestines protrude from the body through the navel.
• Trouble breathing
• Arthrogryposis: presence of contractures in the joints, especially in the extremities.
• Postnatal growth deficiency and developmental delay.
• Cysts in the choroid plexuses, which produce cerebrospinal fluid; they do not cause problems but are a prenatal sign of Edwards syndrome.
• Microcephaly: insufficient development of the head.
• Micrognathia: mandible smaller than expected.
• Cleft palate (cleft lip).
• Malformations in the ears, frequently located lower than usual.
• Wide-set eyes, small, drooping eyelids (ptosis).
• Keel chest or "pigeon chest": the chest protrudes in the area of ​​the sternum.
• Abnormally short sternum
• Absence of the radius, one of the main bones of the forearm.
• Clenched and clenched hands with overlapping fingers.
• Underdeveloped thumbs and nails.
• Convex feet ("in rocking chair")
• Presence of straps that join the toes.
• Cryptorchidism: In males, the testes do not descend properly.
• Weak cry
• Severe intellectual disability.

Causes of Edwards syndrome

The probability of having a baby with trisomy 18 increases with age, being more common around 40 years. Mothers who have already had a daughter or son with this disease have about a 1% chance that the disorder will recur in subsequent pregnancies.

Edwards syndrome is caused by a trisomy of the 18th chromosome. This means that affected babies have three copies of this chromosome, when it is normal to have two pairs of each of the 23. However, trisomy is not always complete, as we will see later.

Trisomy usually occurs because of duplication of the chromosome in the egg or sperm; When the two reproductive cells unite to form the zygote, it develops by dividing successively, and the genetic defect is repeated in each division. At other times, trisomy occurs during the early development of the fetus.

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

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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 can vary depending on the type of trisomy.

1. Complete or classic trisomy

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

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

2. Partial trisomy

Partial trisomy 18 is a rare type of Edwards syndrome caused by incomplete duplication of the chromosome. In general, these cases are due to a translocation, that is, to the breakdown of chromosome 18 and the union 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 alterations are usually less severe than the syndrome classic.

3. Mosaic trisomy

This type of trisomy occurs when extra chromosome 18 is not found in all cells of the baby's body, but in some there are 2 copies and in others 3.

People affected by mosaic trisomy may have severe or mild symptoms, or they may not present any physical changes; however, the risk of premature death remains very high.

Prognosis and treatment

Currently, Edwards syndrome is usually detected before birth by amniocentesis, a test that consists of analyzing the fluid amniotic (which protects the baby and allows it to obtain nutrients) in order to determine possible chromosomal alterations and fetal infections, as well as sex of the baby.

Less than 10% of fetuses with trisomy 18 are born alive. Of these, 90% die in 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 due to cardiac and respiratory disorders.

Edwards syndrome there is no cure, so the treatment is aimed at increasing the quality of life of the affected person as far as possible. Less severe cases of trisomy 18 do not always lead to death in childhood, but they do tend to cause significant health problems, and few patients live longer than 20 or 30 years.

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