Neural tube defects are disorders 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 does not fully form, so babies with this disorder do not live long. Let’s see what the symptoms and causes of anencephaly are and how this defect can be prevented.

What is anencephaly?

Anencephaly is also known as “open-skull approsencephaly. It is a developmental disorder of the neural tube that causes severe disturbances in the growth of the fetus.

In anencephaly the brain and the skull do not develop as expected , but do so incompletely. This causes babies with anencephaly to be born without large regions of the brain, some bones of the head, and portions of the scalp.

This alteration occurs in approximately 1 out of every thousand pregnancies; however, since most times the life of the fetus ends in a miscarriage, the number of babies with anencephaly that are born is 1 out of every 10 thousand newborns. It is more common in girls than in boys.

The defects caused by anencephaly are extremely severe and prevent the baby from being able to live . Most affected infants die within a few hours or days after 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 to be 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, the meninges and the skin. A thin layer of membrane is usually in its place.

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 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 alterations are more marked the larger the part of the brain and skull that 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 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, i.e. the brain and the 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 abnormal development of the neural tube; together 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 brain tissue to spread into the spinal canal.

The 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 impeding normal development of the brain and cerebellum, thus 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, which is 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 significantly.

The homeoprotein CART1, which allows the development of cartilage cells, has also been associated with the appearance

The environmental risk factors affecting the mother are probably more relevant than the genetic ones. Among this type of factors, scientific research highlights the following:

  • Vitamin B9 deficit.
  • Obesity.
  • Diabetes mellitus, especially if it is type I and not controlled.
  • Exposure to high temperatures (e.g. 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 occurs.

Treatment and prevention

Anencephaly cannot be cured . Normally babies born with this problem are given food and water and are made comfortable, but the use of medication, surgery or assisted breathing is considered irrelevant; since the baby will never become conscious, they are usually left to die naturally, without being resuscitated artificially.

Research has shown that 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, such as green leafy vegetables, and in dietary supplements. In the latter case, 0.4 mg per day seems to be sufficient.

However, vitamin B9 intake must be made before pregnancy, since these alterations normally occur during the first phase of fetal development, before a woman detects that she is pregnant. Therefore, specialists recommend increasing the consumption of this vitamin when starting to try to have a baby.