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| Anencephaly Classification and external resources |
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| The anterosuperior view of the head of an anencephalic fetus | ||
| ICD-10 | Q00.0 | |
| ICD-9 | 740.0 | |
| OMIM | 206500 | |
| DiseasesDB | 705 | |
| eMedicine | neuro/639 | |
| MeSH | C10.500.680.196 | |
Anencephaly is a cephalic disorder that results from a neural tube defect that occurs when the cephalic (head) end of the neural tube fails to close, usually between the 23rd and 26th day of pregnancycitation needed, resulting in the absence of a major portion of the brain, skull, and scalp[1]. Children with this disorder are born without a forebrain, the largest part of the brain consisting mainly of the cerebral hemispheres (which include the isocortex, which is responsible for higher level cognition, i.e., thinking). The remaining brain tissue is often exposed - not covered by bone or skin.[2]
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Presentation
The National Institute of Neurological Disorders and Stroke (NINDS) describes the presentation of this condition as follows:
A baby born with anencephaly is usually blind, deaf, unconscious, and unable to feel pain. Although some individuals with anencephaly may be born with a rudimentary 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. [2]
However, the assertion that anencephaly rules out the possibility of consciousness ever being achieved has been specifically disputed.[3]
Diagnosis
Anencephaly can often be diagnosed before birth through an ultrasound examination. The maternal serum alpha-fetoprotein (AFP screening)[4] and detailed fetal ultrasound[5] can be useful for screening for neural tube defects such as spina bifida or anencephaly.
There are many false diagnoses for anencephaly, as it is not a common diagnosis, often confused with exencephaly or microcephaly. Also, sometimes a prognosis stating that an anencephalic baby can live for years is given, often this is the case, but sometimes this cannot occur if the brain is open, because infection sets in rapidly. The anencephalic brain is also usually very disorganised on a cellular level. It depends on the case and individual but often the prognosis is not as grim as it was once reported. There is a support group with much current information under the diagnosis "hydroanencepaly" that is useful in dispelling some of the common myths associated and showing the faces of some of the children affected as they age.citation needed
Prognosis
There is no cure or standard treatment for anencephaly and the prognosis for affected individuals is poor. Most anencephalic babies do not survive birth, accounting for 55% of non-aborted cases. If the infant is not stillborn, then he or she will usually die within a few hours or days after birth from cardiorespiratory arrest.citation needed
In almost all cases anencephalic infants are not aggressively resuscitated since there is no chance of the infant ever achieving a conscious existence. Instead, the usual clinical practice is to offer hydration, nutrition and comfort measures and to "let nature take its course". Artificial ventilation, surgery (to fix any co-existing congenital defects), and drug therapy (such as antibiotics) are usually regarded as futile efforts. Clinicians and medical ethicists may view the provision of nutrition and hydration as medically futile. Occasionally some may even go one step further to argue that euthanasia is morally and clinically appropriate in such cases.citation needed
Rate of occurrence
In the United States, approximately 1,000 to 2,000 babies are born with anencephaly each year. Research has suggested that overall, female babies are more likely to be affected by the disorder.[6]
Causes
The cause of anencephaly is disputed. Neural tube defects do not follow direct patterns of heredity, though there is some indirect evidence of inheritance[7], and recent animal models indicating a possible association with deficiencies of the transcription factor TEAD2.[8] Studies show 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.citation needed
It is known that women taking certain medication for epilepsy and women with insulin dependent diabetes have a higher chance of having a child with a neural tube defect.citation needed Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing.
Recent studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce, although not eliminate, the incidence of neural tube defects. Therefore, it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily,[2] especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%.citation needed It is not advisable to wait until pregnancy has begun, since by the time a woman knows she is pregnant, the critical time for the formation of a neural tube defect has usually already passed. A physician may prescribe even higher dosages of folic acid (4 mg/day) for women who have had a previous pregnancy with a neural tube defect.original research?
Anencephaly and other physical and mental deformities have also been blamed on a high exposure to such toxins as lead, chromium, mercury, and nickel.[9]
Relation to other rare disorders: genetic ciliopathy
Until recently, the medical literature did not indicate a connection among many genetic disorders, both genetic syndromes and genetic diseases, that are now being found to be related. As a result of new genetic research, some of these are, in fact, highly related in their root cause despite the widely-varying set of medical symptoms that are clinically visible in the disorders. Anencephaly is one such disease, part of an emerging class of diseases called cilopathies. 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. Known ciliopathies include primary ciliary dyskinesia, Bardet-Biedl syndrome, polycystic kidney and liver disease, nephronophthisis, Alstrom syndrome, Meckel-Gruber syndrome and some forms of retinal degeneration.[10].
References
- ^ "Cephalic disorders - Overview, Anencephaly, Colpocephaly - neurologychannel". Retrieved on May 2008.
- ^ a b c "Anencephaly Information Page: National Institute of Neurological Disorders and Stroke (NINDS)". Retrieved on 2008-05-08.
- ^ Merker B (2007). "Consciousness without a cerebral cortex: a challenge for neuroscience and medicine". The Behavioral and brain sciences 30 (1): 63–81; discussion 81–134. doi:. PMID 17475053.
- ^ Joó JG, Beke A, Papp C, et al (2007). "Neural tube defects in the sample of genetic counselling". Prenat. Diagn. 27 (10): 912–21. doi:. PMID 17602445.
- ^ Cedergren M, Selbing A (2006). "Detection of fetal structural abnormalities by an 11-14-week ultrasound dating scan in an unselected Swedish population". Acta obstetricia et gynecologica Scandinavica 85 (8): 912–5. doi:10.1080/00016340500448438 (inactive 2008-06-28). PMID 16862467.
- ^ Timson, J. (1970-02-05). "The sex ratio in anencephaly". Genetica 41 (1): 457–465. doi:. Retrieved on 2008-05-08.
- ^ Shaffer LG, Marazita ML, Bodurtha J, Newlin A, Nance WE (1990). "Evidence for a major gene in familial anencephaly". Am. J. Med. Genet. 36 (1): 97–101. doi:. PMID 2333913.
- ^ Kaneko KJ, Kohn MJ, Liu C, Depamphilis ML (2007). "Transcription factor TEAD2 is involved in neural tube closure". Genesis 45 (9): 577–87. doi:. PMID 17868131.
- ^ Goldsmith, Alexander (1996, quoted by Millen and Holtz, "Dying for Growth")
- ^ Badano, Jose L.; Norimasa Mitsuma, Phil L. Beales, Nicholas Katsanis (September 2006). "The Ciliopathies : An Emerging Class of Human Genetic Disorders". Annual Review of Genomics and Human Genetics 7: 125-148. doi:. Retrieved on 2008-06-15.
External links
- Genetic Basis of Anencephaly
- Anencephalie-info.org
- Exencephaly – Anencephaly Sequence and its Sonographic Features
- Images of Anencephaly (Note: Contains graphic medical images)
- Anencephaly, 3D
- Specimens - Anencephaly (Note: Contains graphic medical images)
- Anencephaly info
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Wikipedia content modification information:
- This page was last modified on 31 August 2008, at 03:46.
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