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

This trisomy-related genetic disease is associated with intellectual disability.

Trisomy 18 is more commonly 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 alterations throughout the body and usually causes death before the baby reaches the first year of life.

In this article we will see what are causes and symptoms of this disease and what are the three subtypes of Edwards' syndrome, which differ in the way in which the trisomy is produced.

What is Edwards syndrome?

Edwards' syndrome is a disease caused by genetic faults.Specifically, it occurs as a result of a trisomy, or duplication, of chromosome 18. This is why it is also known as "trisomy 18".

This disorder causes the baby's body to not develop properly, resulting in multiple physical defects and an increased risk of premature death. risk of premature deathTrisomy 18: Only 7.5% of diagnosed babies live more than one 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.

Considering that a large number of spontaneous 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 of them occur simultaneously. The most common of these are described below:

• Malformations in the kidneys.
• Malformations in the heartVentricular septal defects and/or atrial septal defects, patent ductus arteriosus, etc.
• Eating difficulties.
• 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 joint contractures, especially in the extremities.
• Postnatal growth deficiency and developmental delay.
• Cysts in the choroid plexus, which produce cerebrospinal fluid; they do not cause problems but are a prenatal sign of Edwards' syndrome.
• Microcephalyinsufficient development of the head.
• Micrognathia: undersized jaw.
• Cleft palate (cleft lip).
• Malformations in the ears, frequently located lower than usual.
• Wide-set eyes, small and drooping eyelids (ptosis).
• Keeled 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.
• Closed and tightly clasped hands with overlapping fingers.
• Underdeveloped thumbs and nails.
• Convex ("rocker") 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, being more common around age 40. 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 chromosomes. However, the trisomy is not always complete, as we will see later.

Trisomy is usually caused by the duplication of the duplication of the chromosome in the egg or in the sperm; when the two reproductive cells meet.When the two reproductive cells unite to form the zygote, the zygote develops by dividing successively, and the genetic defect is repeated at each division. On other occasions, trisomy occurs during early fetal development.

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

Types of trisomy 18

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

1. Complete or classical trisomy

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

Since the involvement is widespread, in cases of complete trisomy the symptoms are usually more severe. symptoms are usually more severe than in other types of than in the other 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, the breakage 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 alterations 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 all the cells of the baby's body, but in some there are two copies of the same chromosome.but in some there are 2 copies and in others there are 3.

People affected by mosaic trisomy may have severe or mild symptoms, or no physical changes at all; 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 amniotic fluid (which protects the baby and allows it to obtain nutrients) in order to determine possible chromosomal alterations and fetal infections, as well as the baby's sex.

Less than 10% of fetuses with trisomy 18 are born alive. Of these, 90% die within the first year, 90% die within the first year of lifehalf of them within the first week. The average life expectancy for babies with Edwards' syndrome is between 5 days and 2 weeks. Death usually results from cardiac and Respiratory abnormalities.

Edwards' syndrome syndrome has no cure, so treatment is aimed at increasing the affected person's quality of life as much as possible. of the affected person as much as possible. Less severe cases of trisomy 18 do not always result in death in infancy, but they do cause significant health problems and few patients live longer than 20 or 30 years.