Skip Navigation
Genetics Home Reference: your guide to understanding genetic conditions
http://ghr.nlm.nih.gov/     A service of the U.S. National Library of Medicine®

Anencephaly

Reviewed February 2011

What is anencephaly?

Anencephaly is a condition that prevents the normal development of the brain and the bones of the skull. This condition results when a structure called the neural tube fails to close during the first few weeks of embryonic development. The neural tube is a layer of cells that ultimately develops into the brain and spinal cord. Because anencephaly is caused by abnormalities of the neural tube, it is classified as a neural tube defect (NTD).

If the neural tube fails to close properly, the developing brain and spinal cord are exposed to the amniotic fluid that surrounds the fetus. This exposure causes the nervous system tissue to break down (degenerate). As a result, people with anencephaly are missing large parts of the brain called the cerebrum and cerebellum. These brain regions are necessary for thinking, hearing, vision, emotion, and coordinating movement. The bones of the skull are also missing or incompletely formed.

Almost all babies with anencephaly die before birth or within a few hours or days after birth.

How common is anencephaly?

Anencephaly is one of the most common types of neural tube defect, affecting about 1 in 1,000 pregnancies. However, most of these pregnancies end in miscarriage, so the prevalence of this condition in newborns is much lower. An estimated 1 in 10,000 infants in the United States is born with anencephaly.

What genes are related to anencephaly?

Anencephaly is a complex condition that is likely caused by the interaction of multiple genetic and environmental factors. Some of these factors have been identified, but many remain unknown.

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.

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 this vitamin 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.

Related Gene(s)

Changes in this gene are associated with anencephaly.

  • MTHFR

How do people inherit anencephaly?

Most cases of anencephaly are sporadic, which means they occur in people with no history of the disorder in their family. A small percentage of cases have been reported to run in families; however, the condition does not have a clear pattern of inheritance. For parents who have had a child with anencephaly, the risk of having another affected child is increased compared to the risk in the general population.

Where can I find information about diagnosis or management of anencephaly?

These resources address the diagnosis or management of anencephaly and may include treatment providers.

  • Genetic Testing Registry: Anencephalus (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0002902)
  • Genetic Testing Registry: Neural tube defect (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0027794)
  • Genetic Testing Registry: Neural tube defects, folate-sensitive (http://www.ncbi.nlm.nih.gov/gtr/conditions/C1866558)
  • Lab Tests Online: Neural Tube Defects (http://labtestsonline.org/understanding/conditions/neural-tube/start/2)

You might also find information on the diagnosis or management of anencephaly in Educational resources (http://www.ghr.nlm.nih.gov/condition/anencephaly/show/Educational+resources) and Patient support (http://www.ghr.nlm.nih.gov/condition/anencephaly/show/Patient+support).

General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook. Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).

To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

Where can I find additional information about anencephaly?

You may find the following resources about anencephaly helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for anencephaly?

  • anencephalia
  • anencephalus
  • aprosencephaly
  • congenital absence of brain

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about anencephaly?

Ask the Genetic and Rare Diseases Information Center (http://rarediseases.info.nih.gov/GARD/).

What glossary definitions help with understanding anencephaly?

cerebellum ; cerebrum ; congenital ; deficiency ; diabetes ; diabetes mellitus ; embryonic ; fetus ; fever ; folate ; inheritance ; nervous system ; pattern of inheritance ; population ; prevalence ; protein ; risk factors ; seizure ; sporadic ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary (http://www.ghr.nlm.nih.gov/glossary).

References

  • Au KS, Ashley-Koch A, Northrup H. Epidemiologic and genetic aspects of spina bifida and other neural tube defects. Dev Disabil Res Rev. 2010;16(1):6-15. doi: 10.1002/ddrr.93. Review. (http://www.ncbi.nlm.nih.gov/pubmed/20419766?dopt=Abstract)
  • Bassuk AG, Kibar Z. Genetic basis of neural tube defects. Semin Pediatr Neurol. 2009 Sep;16(3):101-10. doi: 10.1016/j.spen.2009.06.001. Review. (http://www.ncbi.nlm.nih.gov/pubmed/19778707?dopt=Abstract)
  • Botto LD, Moore CA, Khoury MJ, Erickson JD. Neural-tube defects. N Engl J Med. 1999 Nov 11;341(20):1509-19. Review. (http://www.ncbi.nlm.nih.gov/pubmed/10559453?dopt=Abstract)
  • Copp AJ, Greene ND. Genetics and development of neural tube defects. J Pathol. 2010 Jan;220(2):217-30. doi: 10.1002/path.2643. Review. (http://www.ncbi.nlm.nih.gov/pubmed/19918803?dopt=Abstract)
  • Doudney K, Grinham J, Whittaker J, Lynch SA, Thompson D, Moore GE, Copp AJ, Greene ND, Stanier P. Evaluation of folate metabolism gene polymorphisms as risk factors for open and closed neural tube defects. Am J Med Genet A. 2009 Jul;149A(7):1585-9. doi: 10.1002/ajmg.a.32937. (http://www.ncbi.nlm.nih.gov/pubmed/19533788?dopt=Abstract)
  • Greene ND, Stanier P, Copp AJ. Genetics of human neural tube defects. Hum Mol Genet. 2009 Oct 15;18(R2):R113-29. doi: 10.1093/hmg/ddp347. Review. (http://www.ncbi.nlm.nih.gov/pubmed/19808787?dopt=Abstract)
  • Obeidi N, Russell N, Higgins JR, O'Donoghue K. The natural history of anencephaly. Prenat Diagn. 2010 Apr;30(4):357-60. doi: 10.1002/pd.2490. (http://www.ncbi.nlm.nih.gov/pubmed/20198650?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: February 2011
Published: July 7, 2014