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 alterations 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 the way trisomy occurs.
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What is Edwards syndrome?
Edwards syndrome is a disease caused by genetic failures ; 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 alteration causes the body of the baby not to develop properly, so that multiple physical defects occur and increases the risk of premature death : only 7.5% of diagnosed babies arrive to live more 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.
Taking into account that a large number of spontaneous abortions occur as a result of this alteration, especially in the second and third trimesters, the prevalence is raised 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 denote the presence of Edwards syndrome, although not all occur simultaneously. Next we will describe the most habitual ones:
- Malformations in the kidneys.
- Malformations in the heart : defects in the ventricular septum and / or in the atrial, persistent ductus arteriosus, etc.
- Difficulties to eat
- Esophageal atresia: the esophagus is not connected to the stomach, so the nutrients do not reach it.
- Omphalocele: the intestines protrude from the body through the navel.
- Difficulty breathing
- Arthrogryposis: the presence of contractures in the joints, especially in the extremities.
- Deficiency in postnatal growth and development delay.
- Cysts in the choroid plexus, which produce cerebrospinal fluid; They do not cause problems but they are a prenatal sign of Edwards syndrome.
- Microcephaly : insufficient development of the head.
- Micrognathia: lower jaw than expected.
- Cleft palate (cleft lip)
- Malformations in the ears, often located lower than usual.
- Widely separated eyes, small drooping eyelids (ptosis).
- Thorax in keel or "chest of pigeon": the chest protrudes in the area of the sternum.
- Abnormally short sternum.
- Absence of the radius, one of the main bones of the forearm.
- Hands closed and tight with fingers overlapping.
- Thumbs and little developed nails.
- Convex feet ("in rocking chair")
- Presence of straps that join the toes.
- Cryptorchidism: in males, the testicles do not descend adequately.
- Weeping weak
- Severe intellectual disability .
Causes of Edwards syndrome
The probability of having a baby with trisomy 18 increases with age, being more common around the age of 40. Mothers who have already had a daughter or son with this disease have about a 1% chance that the disorder will be repeated in later pregnancies.
Edwards syndrome occurs due to 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, the trisomy is not always complete, as we will see later.
Trisomy usually occurs because of the duplication of the chromosome in the ovum or sperm ; when the two reproductive cells come together to form the zygote, it develops by dividing successively, and the genetic defect is repeated in each division. On other occasions trisomy occurs during the early development of the fetus.
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 give rise to the different types of trisomy 18.
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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 depending on the type of trisomy.
1. Complete or classic trisomy
This is the most common form of Edwards syndrome. In classical trisomy, all cells in the body have three intact copies of chromosome 18.
Since the involvement is very widespread, in cases of complete trisomy the symptoms are usually more severe than in the other types of Edwards syndrome.
2. Partial trisomy
Partial trisomy 18 is an infrequent type of Edwards syndrome produced by incomplete duplication of the chromosome. In general, these cases are due to a translocation, that is, to the breaking of chromosome 18 and the union of the separated part to a different chromosome.
The severity and the specific symptoms of each case of partial trisomy vary greatly because the duplications may affect different segments of the chromosome, but the alterations are usually less severe than the classic syndrome.
3. Trisomy in mosaic
This type of trisomy occurs when extra chromosome 18 is not found in all the cells of the baby's body , but in some there are 2 copies and in 3 others.
People affected by mosaic trisomy may manifest severe or mild symptoms, or present no physical alteration; however, the risk of premature death remains very high.
Prognosis and treatment
Currently Edwards syndrome is usually detected before birth through 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 sex of the baby
Less than 10% of fetuses with trisomy 18 come to be 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 due to cardiac and respiratory disorders.
Edwards syndrome It has no cure, so the treatment is aimed at increasing the quality of life of the affected person as far as possible. The less severe cases of trisomy 18 do not always lead to death in childhood, but they do cause important health problems and few patients live more than 20 or 30 years.
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