Anencephaly is a group of malformations of the central nervous system known as neural tube defects. It is a disorder of the head (cephalic). It occurs when the cephalic end of the neural tube fails to close. The process happens between the 23rd and 26th day of the pregnancy. This will result to the absence of a major portion of the brain, skull, and scalp. The affected fetus will be born without a forebrain (the largest part of the brain consisting mainly of the cerebral hemispheres). The remaining brain tissue is often exposed (not covered by bone or skin). In the United States, approximately 1 out of 1,000 to 2,000 babies are born with anencephaly each year. From the studies made, female babies are more likely to be affected. In approximately 10% of cases, other malformations coexist with anencephaly.
Presentation
The National Institute of Neurological Disorders and Stroke (NINDS) describe the presentation of this condition as follows:
- post delivery, the affected baby usually blind, deaf, unconscious, and unable to feel pain
- Some affected fetus may be born with a main brain stem. The lack of a functioning cerebrum permanently rules out the possibility of ever gaining consciousness.
- Reflex actions such as breathing and responses to sound or touch may occur for a limited period.
Diagnosis
- Antenatally, it can be diagnosed by ultrasound examination – detailed fetal ultrasound is useful
- Maternal serum alpha-fetoprotein (AFP screening) – The level of alpha-fetoprotein in the maternal blood is elevated because of the leakage of this fetal protein into the amniotic fluid
Prognosis
The only treatment for these babies are tender, loving and care. We only provide nutrition, hydration and comfort. No active resuscitation done. Artificial ventilation, surgery and drug therapy regarded as futile efforts. Some clinicians and medical ethicists will take nutrition and hydration as medically futile. I myself think that we should do anything for the comfort of the babies before nature takes place as long as no harm is done. There is no cure for this type of disorder. Most affected babies do not survive birth (55% of non-aborted cases). Most of the babies are stillborn, others usually die within a few hours or days after birth from cardiorespiratory arrest. The overall prognosis is poor where the fetus usually fatal at birth or soon thereafter.
Causes
The cause of anencephaly is unclear. There is some evidence of inheritance but it does not follow the direct pattern of heredity. From a developmental point of view, there is a direct association between an impairment of the fetus’s swallowing mechanism and the occurrence of anencephaly. The reason for impairment still remain unknown. Studies have shown that a woman who has had one child with a neural tube defect such as anencephaly, has about a 3% risk to have another child with a neural tube defect. Other than that, some medication that is taken by pregnant mother such as insulin and antiepileptic agents increase the risk to have a neural tube defect babies. Anencephaly and other physical and mental deformities have also been blamed on a high exposure to such toxins as lead, chromium, mercury, and nickel.
Preconception counseling
For women that have high risk for having a child with neural tube defect should be offered for genetic counseling. Available testing will be informed. Recent studies have shown that folic acid may reduce the risk of the neural tube defects. Therefore, pregnant women and those who are trying to conceive should take 0.4 mg of folic acid daily because we do not want to miss the critical time of the neural tube formation. The risk can be reduced to 0.03%. For women with previous affected child, higher dosages of folic acid (4 mg/day) may be prescribed by the physician.
Relation to Other Rare Disorders: Genetic Ciliopathy
As a result of new genetic research, anencephaly is noted to be a part of an emerging class of diseases called “ciliopathies”. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell, organelles which are present in many cellular types throughout the human body. The cilia defects adversely affect “numerous critical developmental signaling pathways” essential to cellular development and thus offer a plausible hypothesis for the often multi-symptom nature of a large set of syndromes and diseases.
Other ciliopathies include:
- primary ciliary dyskinesia
- Bardet-Biedl syndrome
- polycystic kidney
- liver disease
- nephronophthisis
- Alstrom syndrome
- Meckel-Gruber syndrome
- some forms of retinal degeneration
Reference:
- http://en.wikipedia.org/wiki/Anencephaly
- Oxford Handbook of Clinical Specialties. 5th edition. 2001.
- http://www.answers.com/topic/anencephaly
