Anencephaly: Difference between revisions
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==Epidemiology and Demographics== | ==Epidemiology and Demographics== | ||
===Incidence=== | ===Incidence=== | ||
In 2001, [[ National Center for Health Statistics]] reported 9.4 | In the [[United States]], approximately 1,000 to 2,000 babies are born with anencephaly each year. In 2001, the [[National Center for Health Statistics]] reported 9.4 cases among 100,000 live births | ||
===Demographics=== | ===Demographics=== | ||
The highest prevalence has been seen among the Hispanic population. Female babies, whites and children born to mothers who are at extreme of ages are more likely to be affected by the disorder. | The highest prevalence has been seen among the Hispanic population. Female babies, whites and children born to mothers who are at extreme of ages are more likely to be affected by the disorder. Worldwide, Ireland and British Islands has higher prevalence as compared to Asia and Africa which has a lower prevalence rate. | ||
===Recurrence rate=== | ===Recurrence rate=== | ||
Like any other [[neural tube defect]], the [[recurrence rate]] of [[anencephaly]] is 2-4% if one sibling is affected and 10 percent if two siblings are affected. This familial tendency is due to genetics, environmental factors, or both. | Like any other [[neural tube defect]], the [[recurrence rate]] of [[anencephaly]] is 2-4% if one sibling is affected and 10 percent if two siblings are affected. This familial tendency is due to genetics, environmental factors, or both. | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
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| Anencephaly | ||
 | ||
|---|---|---|
| The side view of the head of an anencephalic fetus | ||
| ICD-10 | Q00.0 | |
| ICD-9 | 740.0 | |
| OMIM | 206500 | |
| DiseasesDB | 705 | |
| MeSH | C10.500.680.196 | |
Overview
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 pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp. 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.
Historical Perspective
Classification
Pathophysiology
The cause of anencephaly is disputed. Neural tube defects do not follow direct patterns of heredity, though there is some indirect evidence of inheritance[1], and recent animal models indicating a possible association with deficiencies of the transcription factor TEAD2.[2]
Causes
Anencephaly and other physical and mental deformities have also been blamed on a high exposure to such toxins as lead, chromium, mercury, and nickel. [3]
Differentiating Anencephalopathy from other Disorders
There are many false diagnoses for anencephaly, as it is not a common diagnosis, often confused with exencephaly or microcephaly.
Epidemiology and Demographics
Incidence
In the United States, approximately 1,000 to 2,000 babies are born with anencephaly each year. In 2001, the National Center for Health Statistics reported 9.4 cases among 100,000 live births
Demographics
The highest prevalence has been seen among the Hispanic population. Female babies, whites and children born to mothers who are at extreme of ages are more likely to be affected by the disorder. Worldwide, Ireland and British Islands has higher prevalence as compared to Asia and Africa which has a lower prevalence rate.
Recurrence rate
Like any other neural tube defect, the recurrence rate of anencephaly is 2-4% if one sibling is affected and 10 percent if two siblings are affected. This familial tendency is due to genetics, environmental factors, or both.
Risk Factors
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. 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. Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing.
Screening
Natural History, Complications, 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.
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.
Diagnosis
Diagnostic Criteria
History and Symptoms
Infants born with anencephaly are usually blind, deaf, unconscious, and unable to feel pain.
Physical Examination
Neurologic
Reflex actions such as breathing and responses to sound or touch may occur. Although some individuals with anencephaly may be born with a rudimentary brainstem, which controls autonomic and regulatory function, the lack of a functioning cerebrum is usually thought of as ruling out the possibility of ever gaining consciousness, even though it has been disputed specifically. [4]
Laboratory Findings
Ultrasound
Anencephaly can often be diagnosed before birth through an ultrasound examination. The maternal serum alpha-fetoprotein (AFP screening)[5] and detailed fetal ultrasound[6] can be useful for screening for neural tube defects such as spina bifida or anencephaly.
Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Prevention
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, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%.[7] 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.
References
- ↑ 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:10.1002/ajmg.1320360119. 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:10.1002/dvg.20330. PMID 17868131.
- ↑ Goldsmith, Alexander (1996, quoted by Millen and Holtz, "Dying for Growth")
- ↑ 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:10.1017/S0140525X07000891. 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:10.1002/pd.1801. 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. PMID 16862467.
- ↑ Template:NINDS
Template:Congenital malformations and deformations of nervous system
de:Anenzephalie it:Anencefalia he:אננצפלוס nl:Anencefalie fi:Aivottomuus sv:Anencefali