Neural tube defects are alterations that occur during the first weeks of fetal development and cause malformations of varying severity. While some of them are incompatible with life, others may 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 they are symptoms and causes of anencephaly and how this defect can be prevented.
Anencephaly is also known as “open skull aprosencephaly.” It is a disorder of the development of the neural tube that causes serious alterations in the growth of the fetus.
In anencephaly the brain and skull do not develop as expected, but they do it 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, so the brain is partially exposed.
This alteration occurs in approximately 1 in 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 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 some degree, while if these regions are absent we speak of total anencephaly.
Symptoms and signs
In babies affected by anencephaly, the telencephalon, which contains the cortex and therefore the cerebral hemispheres, is usually absent; The same happens with the skull, meninges and skin. In its place is usually a thin layer of membrane.
Consequently, anencephaly causes the baby to be unable to carry out basic or higher functions, like feeling pain, hearing, seeing, moving, feeling emotions, or thinking, even though in some cases they may issue reflex responses. This means that children with this alteration never become aware of their surroundings.
In addition to these signs and symptoms, facial abnormalities 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 development of the neural tube which 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 spinal cord. In this specific case, the tube does not close at its rostral or upper end.
There are other alterations that are 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 spinal column closes incompletely, and Chiari malformations, which cause brain tissue to spread to the spinal canal.
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 appear to increase the risk of anencephaly, although not very significantly.
The homeoprotein CART1, which allows the development of cartilage cells, has also been associated with the appearance
Environmental risk factors that affect the mother are probably more relevant than genetic ones. Among these types of factors, scientific research highlights the following:
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 can’t be cured Normally, babies born with this problem are given water and food and care is taken to make them comfortable, but the use of medication, surgery or assisted breathing is considered irrelevant; Since the child will never gain consciousness, they are usually allowed to die naturally, without artificially resuscitating them.
Research has shown that the consumption of 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.
