Neural tube defects are changes that occur during the first few weeks of fetal development and cause malformations of varying severity. While some of them are incompatible with life, others can only cause mild paralysis.
The case of anencephaly is particularly serious; the brain is not fully formed, so babies with this disorder do not live long. Let’s see what they are symptoms and causes of anencephaly and how this defect can be avoided.
What is anencephaly?
Anencephaly is also known as “open skull aprosencephaly”. It is a developmental disorder of the neural tube that causes severe alterations in fetal growth.
In anencephaly the brain and skull are not developing as expected, But they do it incompletely. This produces babies with anencephaly without large areas of the brain, without bones in the head, and without parts of the scalp, so the brain is partially exposed.
This change occurs in about 1 in a thousand pregnancies; but, since most of the fetal life ends in miscarriage, the number of anencephalic babies born is 1 in 10,000 newborns. It is more common in girls than in boys.
The defects caused by anencephaly are extremely serious and they prevent the baby from living. Most affected children die within hours or days of birth, although there have been cases of children with anencephaly who have lived for almost 4 years.
Anencephaly can be total or partial. It is considered partial when the roof of the skull, the optic vesicles and the back of the brain are developed to a certain extent, while if these regions are absent, it is called total anencephaly.
Symptoms and signs
In infants with anencephaly, the telencephalon, which contains the cortex and therefore the cerebral hemispheres, is usually absent; the same goes for the skull, meninges and skin. Instead, it usually finds a thin layer of membrane.
As a result, anencephaly prevents the baby from performing basic or higher functions, how to feel pain, feel, see, move, feel emotions or think, Although in some cases they may emit reflex responses. This means that children with this disorder never become aware of their surroundings.
In addition to these signs and symptoms, facial abnormalities and heart defects are common. The changes are all the more marked as the part of the brain and the skull is absent.
The diagnosis of anencephaly can be made during pregnancy through different procedures. Ultrasound can reveal the presence of polyhydramnios (excess amniotic fluid), while amniocentesis can detect high levels of alpha-fetoprotein.
Causes of this alteration
Anencephaly occurs as a result of failure of the neural tube to develop which usually occurs during the fourth week of embryonic development. The neural tube is the structure that gives rise to the central nervous system, that is, the brain and spinal cord. In this particular case, the tube does not close at its rostral or upper end.
There are other alterations due to abnormal development of the neural tube; together they are known as “neural tube defects” and, in addition to anencephaly include spina bifida, In which the spine closes incompletely and Chiari malformations, which cause brain tissue to spread to the spinal canal.
Failure of the neural tube to close properly causes the amniotic fluid that protects the fetus to come into contact with the nervous system, damaging the neural tissue and preventing the normal development of the brain and cerebellum, and therefore causing deficits or even absence. . functions associated with them.
Genetic and environmental risk factors
Usually, the appearance of this defect does not depend on inheritance but on a combination of genetic and environmental factors. However, some cases have been detected in which anencephaly has occurred multiple times in the same family, and having a baby with anencephaly increases the risk that it will also occur in successive pregnancies.
The specific hereditary mechanism by which this occurs is not known, although it is believed that there is a relationship between anencephaly and the MTHFR gene, involved in the treatment of vitamin B9, also called folic acid or folic acid. Alterations in this gene appear to increase the risk of anencephaly, but not very significantly.
The homeoprotein CART1, which enables the development of cartilage cells, has also been associated with the development of
Environmental risk factors affecting the mother are probably more relevant than genetics. Among these types of factors, scientific research highlights the following:
- Vitamin B9 deficiency.
Diabetes mellitus, especially if it is type I and uncontrolled.
- Exposure to high temperatures (eg fever, saunas).
- consumption of anticonvulsant drugs such as lamotrigine.
It also appears that anencephaly is more common in babies born to Asian, African and Hispanic mothers, although it is not known what causes this increased risk.
Treatment and prevention
Anencephaly it cannot be cured. Babies born with this problem are usually given food and water and feel comfortable, but the use of medication, surgery, or breathing assistance is not considered relevant; since the infant never acquires consciousness, it is generally allowed to die naturally, without being artificially resuscitated.
Research has shown that the intake of folic acid (vitamin B9) Significantly reduces the risk of neural tube defects, including anencephaly and spina bifida. This vitamin is found both in foods, for example green leafy vegetables, and in food supplements; in this second case, 0.4 mg per day seems to be sufficient.
However, vitamin B9 intake should be done before pregnancy, as these alterations usually occur during the first phase of fetal development, before the woman recognizes that she is pregnant. Thus, specialists recommend increasing the consumption of this vitamin when you start trying to have a baby.