Trisomy 18 life expectancy
Trisomy 18 is a genetic disease in which the chromosome 18 is three-fold rather than two-fold. This disrupts many developmental processes of the organism. Most children with trisomy 18 die already before or soon after birth.
Since the first description by Dr. Edwards in 1960, the trisomy 18 is also called Edwards syndrome. Read more about this disease: What is Trisomy 18 exactly? What are the symptoms? What is diagnosis, treatment and prognosis?
Trisomy 18 is a severe hereditary disease that is caused by a faulty distribution of chromosomes on the newly emerging cells. Chromosomes are the carriers of heredity (genes). In humans with trisomy 18, the chromosome 18 is present in the cells in triple rather than duplicate. This disturbs the development of a child already in the mother’s body and causes various organ malformations.
As a result, more than 95 percent of all affected children die before birth, often already in the first trimester. Life expectancy of live-born trisomy 18 children is not very high.
Trisomy 18 was first published in 1960 by the British Dr. John Edwards and therefore it is also called Edwards syndrome.
Different forms of Trisomy 18
Depending on the development of the fertilized egg, the chromosomal disorder is affected by more or less cells of the child from Trisomy 18. Thus, different forms of trisomy are differentiated:
Free trisomy: Accounts for 94 percent of all cases of trisomy 18. All cells have a third (over surplus) chromosome 18.
Mosaic trisomy: Accounts for about five percent of all cases of sickness. Only individual cell lines have the trisomy. All other cells of the body have the correct number of chromosomes and work flawlessly.
Translocation trisomy: accounts for about one percent of all cases of illness. A portion of chromosome 18 is present in triplicate and attached to another chromosome. Professionals also speak of partial trisomy as a result of translocation.
Life expectancy of a baby with trisomy 18
Babies with trisomy can survive six to nine days with fifty percentage. About 12% of babies can surivive one year. It is difficult to predict the life expectancy of a baby with trisomy 18 if the baby does not have any immediate life-threatening problems. For babies that have survived their first 30 days of life, 36% were alive at one year. About 10% of children born with trisomy 18 survive until 10 years of age.
Trisomy 18 Symptoms
Children who are born with a trisomy 18 often have characteristic signs that point to Edwards syndrome. Which includes:
- Low birth weight
- Finger overlays
- Small facial, small mouth, small, backward-receding chin
- Faunal ears
- Cleft palate
- Congenital heart defects
- Renal malformations
- Ureter malformations
- Brain malformation
- Lung malformation
- The affected children often have nutritional problems and growth is delayed. Many of the small patients cannot go free and speak only a few words.
This frame of trisomy 18 is shown above all in a free trisomy. In the case of Mosaictrisomy, on the other hand, the symptoms can be less pronounced, especially if only a few cell lines are affected by the chromosome disorder.
Trisomy 18 Causes and Risk Factors
A trisomy is a chromosome misdistribution in which a chromosome (or part of it) does not occur twice (as usual) but three times in a cell. The risk for this increases, for example, with the age of the becoming mother.
Healthy body cells have 23 pairs of chromosomes (“double chromosomes”) – each pair comes with one copy of the mother and the other from the father. In total, there are 46 chromosomes. The germ cells (egg and sperm cells) have only one “simple chromosome set” (23 chromosomes) – only one copy of each chromosome.
The double chromosome set must be halved in its formation. This is the only way to create a cell with a double set of chromosomes during fertilization by the fusion of an egg cell and a sperm cell. From this, the new organism is formed by innumerable cell divides.
In the formation of germ cells or after fertilization in the development of the fetus or embryos, the error that leads to trisomy 18 may occur:
Free Trisomy 18
In the case of free trisomy, there is already a faulty distribution of chromosome 18 before fertilization of the egg. In more than 90 percent of cases, this erroneous assignment occurs in the formation of the egg (in the remaining cases in the formation of the sperm cell). This error often occurs spontaneously and rarely follows certain inheritance patterns.
Mosaic trisomy 18
In the case of Mosaic trisomy 18, the defect occurs relatively late in the development of the fertilized egg, so that only single cell lines have three chromosomes 18. All other cell lines have the normal number of two chromosomes 18 and therefore they are healthy. The fewer cell lines are affected, the lower the symptoms and the higher the life expectancy.
Translocation trisomy 18
The starting point of this variant is a so-called “balanced translocation” for a parent, mostly the mother: she has the normal number of chromosomes in her cells. However, as a result of a chromosome fracture, a part of chromosome 18 was falsely attached to another chromosome (translocation). However, since all genes of chromosome 18 are present in a normal number (although not in a normal arrangement), this is called “balanced translocation”. The affected parent is completely healthy.
Trisomy 18 Investigations and Diagnosis
In the case of regular ultrasound examinations during pregnancy, the doctor may suspect a chromosomal disorder such as trisomy 18 due to abnormalities in the unborn child. For example, a delayed growth as well as malformations on the abdomen, head or heart of the child which fit into the image of trisomy 18 can be noticed by the doctor. In addition, trisomy 18 is frequently associated with the fact that only one artery (instead of two) is placed in the umbilical cord.
In addition, certain maternal blood values may be increased in a trisomy. This blood test is also known as a triple-test or multiple-median (MoM) test. However, it is not suitable for a reliable diagnosis, but rather is intended to identify mothers who are at increased risk for a trisomy. It helps to assess the risk of a child’s illness without major invasive procedures.
With the triple test, the risk of certain DNA damage to the child can be assessed roughly – it has no great significance. A positive result does not mean trisomy for a long time.
In order to clarify a suspicion of trisomy 18, invasive methods of investigation are often carried out. With the help of the chorionic or the Amniotic water examination, children’s genomes can be gained and examined for chromosomal disorders such as trisomy 18. However, it should be noted that these invasive interventions can harm the child and may even cause a miscarriage.
Trisomy 18 Treatment
Trisomy 18 can not be healed. All therapeutic measures are aimed only at alleviating the symptoms or maintaining the organ functions. For example, if the child has nutritional problems, special suckers or probe nutrition can be helpful.
Monitoring can be useful for breathing problems. The very common heart defects are sometimes operated. A surgical procedure can also be carried out for other organ malformations such as disturbances in urinary discharge. In general, surgical corrections of malformations are carefully considered, because it is unclear whether they actually improve the prognosis and the quality of life of the small patients.
Psychological counseling for parents is useful in many cases, as the death of the child is likely to occur. Especially in the first weeks of life, the life of the newborn child is at risk.
Trisomy 18 prognosis
Most fetuses with trisomy 18 are already dying in the womb during development. And even the few affected children who come to the world usually do not survive long. If organ malformations are already known before birth, childbirth can take place on a postnatal ward with subsequent pediatric maximum care. This can increase the chances of survival for the child.
The average life expectancy of trisomy 18 children is one to two weeks. Only five per cent reach the first year of life, and only one per cent is 10 years old. In individual cases, however, the prognosis depends on various factors, especially on the nature of trisomy 18.
Even if the child survives his first birthday, one must expect serious physical and mental disabilities and development delays. In addition to organ malformations, it is often associated with seizures, severe postural deformity and problems with food intake. In rare cases, patients with trisomy 18 reach the age