Trisomy 18 is characterized by the presence of an extra chromosome 18, within certain cells of the body or in each of these cells. Two forms of the disease are known and the severity of Trisomy depends on it.
Definition of trisomy 18
Trisomy 18, also known as Edwards Syndrome, is a disease caused by chromosomal abnormalities. It is defined by abnormalities in different parts of the body.
Trisomy 18 patients generally have disturbances in their growth before birth (intrauterine growth retardation). As well as an abnormally low weight. Other signs may also be related to the disease: heart attacks, impairments of other organs, etc.
Trisomy 18 also includes other characteristics: abnormal shape of the skull of the child, small jaw and narrow mouth or wrists returned and the fingers which are superimposed.
These different attacks can be vital for the child. In the majority of cases, a child with trisomy 18 dies before birth or before his first month.
Survivors after the first month usually have significant intellectual disabilities.
The risk of Down syndrome is associated with the pregnancy of a woman of any age. In addition, this risk is increased in the context of a late pregnancy.
Two specific forms of the disease have been described:
- The complete form: which concerns nearly 94% of babies with Down syndrome? This form is characterized by the presence of a triple copy (instead of two) of chromosome 18, in each cell of the body. Most babies with this form die before termination of pregnancy.
- The mosaic form, which affects about 5% of babies with trisomy 18. In this context, the triple copy of chromosome 18 is visible only partially within the body (in some cells only). This form is less severe than the complete form.
The severity of the disease therefore depends on the type of trisomy 18 as well as the number of cells containing a copy of chromosome 18, in addition.
The causes of trisomy 18
The majority of Trisomy 18 cases result from the presence of a triple copy of chromosome 18, within each cell of the body (instead of two copies).
Only 5% of individuals with Trisomy 18 have an extra copy, in some cells only. This minority of patients are particularly inclined to risk of death before birth, or before the first month of the child.
Rarer frequency, the long arm of chromosome 18 can attach (translocation) to another chromosome during cell reproduction or during embryonic development. This leads to the presence of the double copy of chromosome 18, coupled with the presence of an additional chromosome 18, and therefore to 3 chromosomes 18. Patients with this particular form of trisomy 18, exhibit partial symptoms.
Who is affected by Trisomy 18?
The risk of trisomy 18 concerns each pregnancy. Moreover, this risk is increased as the age of the pregnant woman increases.
Evolution and possible complications of Trisomy 18
In the majority of cases of Trisomy 18, the death of the child before birth, or running the first month, is associated. In the case where the child survives, sequelae may be visible: developmental delay of certain limbs and / or organs, intellectual disabilities, etc.
The symptoms of trisomy 18
Clinical signs and general symptoms may be similar to Trisomy 18:
- a head smaller than the average
- hollow cheeks and a narrow mouth
- long fingers that overlap
- big ears placed very low
- malformations at the cleft lip
Other features of the disease may be visible:
- kidney and heart disease
- Refusal to eat, leading to deficiencies in the development of the child
- breathing difficulties
- the presence of hernias in the stomach
- Abnormalities in the skeletal system and especially in the spine
- Significant learning difficulties.
Risk factors of Trisomy 18
The risk factor for the development of Trisomy 18 is genetics.
Indeed, the presence of a triple copy of chromosome 18, within certain cells only or at each cell of the body, can lead to the development of such pathology.
How to treat Trisomy 18?
No trisomy 18 treatment is currently known. The management of this disease is effective by a health team, multidisciplinary.
Treatments can nevertheless be prescribed, in the context of heart attacks, infections, or difficulties in eating.
The physiotherapy can also be a support for Trisomy 18, especially if the muscle and bone systems are impacted.