Anencephaly: causes, symptoms and prevention
Neural tube defects are alterations that occur during the first weeks of fetal development and that 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 completely formed, so babies with this disorder do not live for a long time. Let's see what they are the symptoms and causes of anencephaly and how can this defect be prevented.
- Related article: "Macrocephaly: causes, symptoms and treatment"
What is anencephaly?
Anencephaly is also known as "aprosencephaly with an open skull". 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 the skull do not develop as would be expected , but they do it incompletely. This causes babies with anencephaly to be born without extensive regions of the brain, without some bones of the head and without portions of the scalp, so that 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 come to be born is 1 in 10 thousand newborns. It is more common in girls than boys.
The defects caused by anencephaly are extremely severe and they prevent the baby from living . Most of the affected children die a few hours or days after being born, although there have been cases of children with anencephaly who have lived 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 babies affected with anencephaly the telencephalon is usually absent, which contains the cortex and therefore the cerebral hemispheres; the same happens with the skull, the meninges and the skin. Instead, a thin layer of membrane is usually found.
As a result, anencephaly means that the baby can not carry out basic or superior functions, how to feel pain, hear, see, move, feel emotions or think , even though in some cases they can emit reflex responses. This means that children with this alteration never become aware of their environment.
In addition to these signs and symptoms, abnormalities of the face and heart defects are common. The alterations are more marked the greater the absent part of the brain and the 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 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 particular case, the tube does not close at its rostral or upper end.
There are other alterations that are due to an 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 vertebral column closes incompletely, and the Chiari malformations, which cause the brain tissue to spread to the medullary canal.
The fact that the neural tube does not close properly causes the amniotic fluid that protects the fetus to come in 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 these.
Genetic and environmental risk factors
Normally the appearance of this defect does not depend on the inheritance 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 subsequent pregnancies.
The concrete 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 the vitamin B9, also known as folic acid or folate . The alterations in this gene seem to increase the risk of anencephaly, although not in a very significant way.
The CART1 homeoprotein, which allows the development of cartilage cells, has also been associated with the appearance
The environmental risk factors that affect the mother are probably more relevant than the genetic ones. Among this type of factors, scientific research highlights the following:
- Deficit of vitamin B9.
- Diabetes mellitus, especially if it is type I and is not controlled.
- Exposure to high temperatures (eg fever, saunas).
- Consume of anticonvulsant medications such as lamotrigine .
It also seems that anencephaly is more common in babies born to Asian, African and Hispanic mothers, although it is not known why this increase in risk is due.
Treatment and prevention
Anencephaly it can not be cured . Babies born with this problem are usually given water and food and are comfortable, but it is considered that the use of medication, surgery or assisted breathing is irrelevant; since the child will never acquire consciousness, they are usually allowed to die naturally, without artificially resurrecting them.
Research has shown that the Folic acid intake (vitamin B9) greatly reduces the risk of neural tube defects, including anencephaly and spina bifida. This vitamin is found in foods, such as green leafy vegetables, as well as in dietary supplements; in this second case, 0.4 mg daily seems to be enough.
However, the intake of 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.