Anencephaly

Overview of Anencephaly

Neurological disorders mainly encompass the disorders pertaining to the central and the peripheral nervous system. Nearly, 1 billion people worldwide or 1 in every 6 people in a given population suffers from different types of neurological disorders belonging to either of the above types. 

Possibly the most serious form of the neurological disorder is the neural tube defect. It mainly belongs to a class of cephalic disorders. This article will discuss the most commonly studied type of cephalic disorder or neural defect namely- Anencephaly. It is a major cranial defect. The fetus affected with the disease often dies in the gestation period itself. Research initiatives in different countries are being directed to treat these kinds of neural tube defects and reduce the burden of fetal mortality.

What is Anencephaly?

An anencephaly is a severe form of central nervous system disorder in which the cranial vault and the brain are poorly developed. Many research scientists have defined it as the condition in which a significant portion of the brain, skull and the scalp are not present at the time of embryonic development. Usually, within the 23^rd to the 26^th day after conception, a major neural tube defect is observed in many cases. This is basically a type of cephalic disorder in which the rostral (head) end of the neural tube fails to close partially or completely.

If the term “Anencephaly”, which is originally a Greek word, is translated it means that the inside part of the head, that is the brain is totally lacking. In reality, these children usually lack the main part of the brain, that is the “telencephalon”.  This is the largest part of the brain that comprises of the cerebral lobes and the neocortex and regulates the different cognitive functions. The residual structures of the brain are loosely covered by a very thin layer of membrane. The skin, meninges, and the bones, all are usually absent. Barring a few rare cases, infants born with Anencephaly do not live for more than a few hours or a few days.

Epidemiology

The incidence rates of Anencephaly are higher in a few geographical regions like China, Mexico, Guatemala and certain parts of the United Kingdom. Typically, the Hispanic and non-Hispanic white women are affected more than the women of African origin. In the United States, the incidence rate is about 1.2 per 10,000 births and about 1 in every 1000 pregnancies. Recently, the studies of the Center for Disease Control and Prevention have shown a 21% decline in the occurrence of Anencephaly in the United States.

What are the main causes of Anencephaly?

Anencephaly is an isolated birth defect. It arises from a number of genetic, dietary and environmental factors. These are described below-

• Folic acid: Sufficient folic acid intake is critical to fetal development, especially in the first few weeks of pregnancy. A deficiency of Folic Acid in the regular diet and in the mother’s body increases the risks of Anencephaly. Often, exposure to certain agents that interfere with the folate metabolism, especially during the first 6 weeks of pregnancy (crucial period of neural tube development) also increases the possibilities of Anencephaly manifold. The mothers should abstain from the anti-metabolites of Folic acids, such as a Valproic acid (anticonvulsant), at least in the first few weeks of pregnancy.
• Diabetes: Pre-gestational Insulin Dependent Diabetes Mellitus (IDDM) delays the generation of alpha-fetoprotein (AFP) during pregnancy and thereby increases the risks for Anencephaly.
• Maternal hyperthermia: Hyperthermia means an increase in the body temperature. Pregnant women are advised not to take frequent hot baths or stay for a long period in hot and humid environments, since both the conditions may induce transient hyperthermia in the mother’s body. This along with gestational fever can confer an increase in the chances of Anencephaly and other Neural Tube Defects.
• Genetics: Anencephaly has been traced back to Autosomal Dominant or Autosomal Recessive traits that run in families. The disease is also associated with the unbalanced form of a structural chromosomal abnormality in a few cases.
• Amniotic Band Disruption Sequence: In this condition, rupture of the amniotic membranes occurs. This impedes the formation of tissues and the cranial structures during fetal development. Anencephaly caused by this condition is usually marked by the presence of residues of amniotic membrane.

What are the main signs and symptoms?

The following signs are typically observed-

• Problems in audio-visual functions
• Being unaware of the surroundings
• Lack of pain sensation
• Presence of only the basic reflex actions like breathing and touch sensation

What are the main types of Anencephaly?

Given below is a list of the types of Anencephaly identified so far-

• Meroanencephaly: It is a rare form of Anencephaly, wherein the patient has a median cranial defect, deformed cranial bones and an abnormal cranial bulging known as area
• Holo anencephaly: It is the most commonly observed form of Anencephaly where the brain is completely missing.
• Craniorachischisis: It is the most severe form of Anencephaly marked by spinal defects and exposed neural tissues. Here, the area cerebrovasculosa and the area medullovasculosa fill the spinal column as well as the cranial defects.

Diagnosis, treatment, & prevention

The following diagnostic tests are normally recommended for detecting the presence of Anencephaly-

• Maternal Serum Alpha-Fetoprotein (MSAFP) screening
• Amniotic Alpha-Fetoprotein (AFAFP) test
• Acetylcholinesterase (ACHE) test
• Cytogenic testing
• MRI and CT scans (postnatal)
• Pre-natal 2-dimensional ultrasound examination

There is no standard and absolute treatment for Anencephaly. The serious symptoms can be controlled through anticonvulsants or other neurological medications. Neurosurgeries may be recommended in certain cases to rectify the facial defects. Usually, a fetus with neural tube defects either ends in miscarriage or results in stillbirth. The few which are born succumb to the condition within hours. The most effective way to prevent anencephaly is getting adequate folic acid and limiting exposure to environmental pollutants such as tobacco and toxic metals.

 
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