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 results in 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.

    What is Edwards Syndrome?

    Edwards syndrome is a disease caused by genetic errors; in particular, 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 prevents the baby’s body from developing properly, resulting in multiple physical defects and increased risk of premature death: Only 7.5% of babies diagnosed live longer than a year.

    It is a very common disease affecting 1 in 5,000 newborns, most of whom are women. In fact, it is the most common trisomy after Down syndrome, in which chromosome 21 is duplicated.

    Given that a large number of miscarriages occur as a result of this alteration, especially in the second and third trimesters, the prevalence increases if one refers to the fetal period rather than the perinatal period.

      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 describe the most common:

      • Kidney malformations.
      • Heart defects: Defects of the ventricular and / or atrial septum, persistent ductus arteriosus, etc.
      • Difficulty in 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 lungs.
      • Difficulty in breathing.
      • Arthrogryposis: presence of contractures in the joints, in particular the limbs.
      • Postnatal growth deficit 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: jaw smaller than expected.
      • Palate fes (cleft lip).
      • Ear malformations, often located lower than usual.
      • Eyes wide apart, eyelids small and drooping (ptosis).
      • Thorax in the keel or “pigeon breast”: the chest protrudes in the sternum area.
      • Abnormally short sternum.
      • Absence of the radius, one of the main bones of the forearm.
      • Closed and narrow hands with fingers overlapping.
      • Poorly developed thumbs and fingernails.
      • Convex feet (“rocking chair”)
      • Presence of cliffs joining the toes.
      • Cryptorchidism: In men, the testes do not descend properly.
      • Low cry.
      • Severe intellectual disability.

      Causes of Edwards syndrome

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

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

      Down’s syndrome usually occurs due to the duplication of the chromosome in the egg or sperm; when the two reproductive cells come together to form the zygote, the zygote 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 the duplication of chromosome 18, this disease can also be due to other genetic errors, such as translocation. These differences give rise to different types of Down’s syndrome.

        Types of Down’s syndrome

        There are three types of Edwards syndrome depending 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

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

        The attack being generalized, in the event of complete trisomy symptoms are usually more severe than in other types of Edwards syndrome.

        2. Partial trisomy

        Partial trisomy 18 is a rare type of Edwards syndrome caused by incomplete chromosome duplication. Usually, these cases are due to a translocation, that is, the rupture of chromosome 18 and the union of the separated part on a different chromosome.

        The specific severity and symptoms of each case of partial trisomy vary widely as duplications can affect different segments of the chromosome, but the alterations are generally less severe than the classic syndrome.

        3. Mosaic trisomy

        This type of trisomy occurs when the 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 with mosaic trisomy may have severe or mild symptoms, or no physical changes; however, the risk of premature death remains very high.

        Prognosis and treatment

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

        Less than 10% of fetuses with trisomy 18 are born alive. Among these, 90% die within the first year of life, Half of them during the first week. The half-life expectancy of babies with Edwards syndrome is between 5 days and 2 weeks. Death usually occurs due to heart and respiratory problems.

        Edwards syndrome it does not matter, so the treatment aims to improve the quality of life of the affected person to the extent possible. Less severe cases of trisomy 18 do not always lead to death in childhood, but they do lead to serious health problems, and few patients live longer than 20 or 30 years.

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