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Diseases

Genetic and Rare Diseases Information Center (GARD)

Other Names for this Disease
  • Absence of a large part of the brain and the skull
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Overview



What is anencephaly?

What causes anencephaly?

Can anencephaly be inherited?


What is anencephaly?

Anencephaly is a defect in the closure of the neural tube during fetal development. The neural tube is a narrow channel that folds and closes between the 3rd and 4th weeks of pregnancy to form the brain and spinal cord of the embryo. Anencephaly occurs when the 'cephalic' or head end of the neural tube fails to close, resulting in the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain (the front part of the brain) and a cerebrum (the thinking and coordinating part of the brain). The remaining brain tissue is often exposed (not covered by bone or skin). A baby born with anencephaly is usually blind, deaf, unconscious, and unable to feel pain.[1] Most cases are stillborn, although some infants have been reported to survive for a few hours or even a few days.[2] Reflex actions such as breathing and responses to sound or touch may occur.[1]
Last updated: 11/28/2011

What causes anencephaly?

The cause of anencephaly is not fully understood. Like other forms of neural tube defects (NTDs),this condition is likely caused by the interaction of multiple genes and environmental factors. Some of these factors have been identified, but many remain unknown.[3][1][4]

Changes in dozens of genes may influence the risk of anencephaly. The best-studied of these genes is MTHFR, which provides instructions for making a protein that is involved in processing the B-vitamin folate (also called folic acid or vitamin B9). Changes in other genes related to folate processing and genes involved in the development of the neural tube have also been studied as potential risk factors for anencephaly. However, none of these genes appear to play a major role in causing the condition.[3]

Researchers have also examined environmental factors that could contribute to the risk of anencephaly. A shortage (deficiency) of folate appears to play a significant role. Studies have shown that women who take supplements containing folic acid before they get pregnant and very early in their pregnancy are significantly less likely to have a baby with anencephaly or a related neural tube defect. Other possible risk factors for anencephaly include diabetes mellitus, obesity, exposure to high heat (such as a fever or use of a hot tub or sauna) in early pregnancy, and the use of certain anti-seizure medications during pregnancy. However, it is unclear how these factors may influence the risk of anencephaly.[3]
Last updated: 11/28/2011

Can anencephaly be inherited?

Ninety percent of open neural tube defects happen to couples without a prior family history of these defects.[5] While most neural tube defects (NTDs) are caused by a complex interaction between various genes and environmental factors, rare cases of NTDs are transmitted in an autosomal dominant or autosomal recessive manner in certain families.[2][4] Such families may have children or fetuses with spina bifida, anencephaly, or other subtypes of NTDs.[4]
Last updated: 10/18/2013

References
  1. NINDS Anencephaly Information Page. National Institute of Neurological Disorders and Stroke (NINDS). 2010; http://www.ninds.nih.gov/disorders/anencephaly/anencephaly.htm. Accessed 11/28/2011.
  2. Anencephaly. Orphanet. 2006; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=1048. Accessed 11/28/2011.
  3. Anencephaly. Genetics Home Reference. February 2011; http://ghr.nlm.nih.gov/condition/anencephaly. Accessed 11/28/2011.
  4. Best RG, Gregg AR, Lorenzo N. Anencephaly. eMedicine. 2010; http://emedicine.medscape.com/article/1181570-overview. Accessed 11/28/2011.
  5. Anencephaly. Children's Hospital Boston. 2010; http://www.childrenshospital.org/az/Site578/mainpageS578P0.html. Accessed 11/28/2011.