This developmental disorder causes head malformations in babies during pregnancy.
Neural tube defects are abnormalities that occur during the first weeks of fetal development and cause malformations of varying severity. While some of them are incompatible with life, others can cause only mild paralysis.
The case of anencephaly is particularly severe; the brain is not fully formed, so babies with this disorder do not live long. Let’s see what are the symptoms and causes of anencephaly and how this defect can be prevented.
What is anencephaly?
Anencephaly is also known as “open-skull aprosencephaly.” It is a developmental disorder of the neural tube that causes severe disturbances in the growth of the fetus.
In anencephaly the brain and skull do not develop as expected, but do so incompletely. This causes babies with anencephaly to be born without large regions of the brain, without some bones in the head, and without portions of the scalp, partially exposing the brain.
This alteration occurs in approximately 1 out of every thousand pregnancies; However, since most of the time the life of the fetus ends in a spontaneous abortion, the number of babies with anencephaly that are born is 1 in every 10,000 newborns. It is more common in girls than in boys.
The defects caused by anencephaly are extremely severe and prevent the baby from living. Most of the affected children die a few hours or days after birth, although there have been cases of children with anencephaly who have lived to almost 4 years.
Anencephaly can be total or partial. It is considered to be partial when the roof of the skull, the optic vesicles and the posterior part of the brain are developed to some degree, whereas if these regions are absent we speak of 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 is true of the skull, meninges, and skin. In its place is usually a thin layer of membrane.
Consequently, anencephaly makes the baby unable to carry out basic or higher functions , such as feeling pain, hearing, seeing, moving, feeling emotions or thinking, even though in some cases they can emit reflex responses. This means that the little ones with this alteration never become aware of their environment.
In addition to these signs and symptoms, abnormalities in the face and heart defects are common. The alterations are more marked the greater the missing part of the brain and skull.
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 elevated levels of alpha-fetoprotein.
Causes of this alteration
Anencephaly occurs as a result of a defect in the evolution of the neural tube that normally occurs in 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 the spinal cord. In this particular case, the tube does not close at its rostral or superior end.
There are other alterations that are due to an abnormal development of the neural tube; collectively they are known as “neural tube defects”, and in addition to anencephaly they include spina bifida, in which the spine closes incompletely, and Chiari malformations, which cause the brain tissue to spread to the canal medullary.
The fact that the neural tube does not 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 the absence of the functions associated with them.
Genetic and environmental risk factors
Normally the appearance of this defect does not depend on heredity but on a combination of genetic and environmental factors. However, some cases have been detected in which anencephaly has occurred repeatedly in the same family, and having a baby with anencephaly increases the risk of it also occurring in successive pregnancies.
The specific hereditary mechanism by which this happens is not known, although it is believed that there is a relationship between anencephaly and the MTHFR gene, involved in the processing of vitamin B9, also known as folic acid or folate. Alterations in this gene seem to increase the risk of anencephaly, although not very significantly.
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Environmental risk factors affecting the mother are probably more relevant than genetic ones. Among these types of factors, scientific research highlights the following:
- Vitamin B9 deficiency.
- Diabetes mellitus, especially if it is type I and is not controlled.
- Exposure to high temperatures (eg fever, saunas).
- Consumption of anticonvulsant medications 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 why this increased risk is due.
Treatment and prevention
Anencephaly cannot be cured. Normally, babies born with this problem are given food and water and care is taken to make them comfortable, but the use of medication, surgery, or assisted respiration is considered irrelevant; since the little one will never acquire consciousness, they are usually allowed to die naturally, without being artificially resurrected.
Research has shown that consuming folic acid (vitamin B9) greatly 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 dietary supplements; in this second case, 0.4 mg daily seems to be sufficient.
However, taking vitamin B9 must be done before pregnancy, since these alterations normally occur during the first phase of fetal development, before the woman detects that she is pregnant. Thus, specialists recommend increasing the consumption of this vitamin when you start trying to have a baby.