National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Anencephaly


Other Names:
Absence of a large part of the brain and the skull
Categories:
This disease is grouped under:
Anencephaly is a type of neural tube defect characterized by abnormal development of the brain and the bones of the skull. The neural tube is a narrow channel that normally folds and closes between the 3rd and 4th weeks of pregnancy, forming the brain and spinal cord of the embryo. Anencephaly occurs when the 'cephalic' or head end of the neural tube fails to close, causing 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). Affected babies are usually blind, deaf, unconscious, and unable to feel pain. Almost all babies with anencephaly die before birth, although some may survive a few hours or a few days after birth. Anencephaly is likely caused by an interaction between genetic and environmental factors, many of which remain unknown.[1][2][3]
Last updated: 8/31/2015

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Anencephaly 0002323
Primary adrenal insufficiency 0008207
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance 0000007
Congenital onset
Symptoms present at birth
0003577
Spina bifida 0002414
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Last updated: 7/1/2020
The underlying cause of anencephaly is not fully understood. Like other forms of neural tube defects (NTDs), anencephaly is likely caused by the interaction of multiple genes and environmental factors, many of which remain unknown.[3]

Variations in many genes may influence the risk of developing anencephaly. The best-studied gene thus far is the MTHFR gene, which gives the body instructions to make a protein used to process the vitamin folate (also called vitamin B9). A deficiency of folate is a known risk factor for NTDs. Other genes involved in folate processing, and the development of the neural tube, may also affect the risk.

Researchers have also looked at environmental factors that could contribute to the risk of anencephaly. Folate appears to play a significant role, and studies have shown that taking folic acid (a form of folate), before getting pregnant and very early in pregnancy, significantly reduces the risk to have a baby with a NTD. Other possible maternal 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.[3]
Last updated: 8/31/2015
Most cases of anencephaly are sporadic, which means they occur in people with no family history of anencephaly or other neural tube defects (NTDs). In some cases, it may be associated with a chromosome abnormality, a severe malformation syndrome, or disruption of the amniotic membrane.[4] A small portion of cases have appeared to be familial, but it often does not have a clear inheritance pattern.[3] In isolated populations, anencephaly has been suspected to be due to a single gene. In Iranian Jews, who have high rates of consanguinity (mating with family members), it is inherited in an autosomal recessive manner.[5]

Parents who have had a child with anencephaly are at an increased risk to have another affected child (compared with the risk in the general population).[3] Because most cases are believed to be multifactorial (due to interaction of genetic and environmental factors), the recurrence risk is estimated to be between 2% and 5% after a single case.[5] If anencephaly is known to be associated with an underlying disorder, the recurrence risk may depend on that of the underlying disorder.

For women who have previously had a fetus or infant with anencephaly, the Centers for Disease Control and Prevention (CDC) recommends increasing the intake of folic acid to 4mg per day beginning at least one month prior to conception.[5]

People who have had a pregnancy or child with anencephaly or another NTD, and have questions about future risk, are encouraged to speak with a genetic counselor or other genetics professional.
Last updated: 8/31/2015

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Anencephaly. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

Organizations Providing General Support

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • You can obtain information on this topic from the Centers for Disease Control and Prevention (CDC). The CDC is recognized as the lead federal agency for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States.
  • Genetics Home Reference (GHR) contains information on Anencephaly. This website is maintained by the National Library of Medicine.
  • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
  • The National Institute of Neurological Disorders and Stroke (NINDS) collects and disseminates research information related to neurological disorders. Click on the link to view information on this topic.
  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Anencephaly. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • I have been pregnant three times. My first pregnancy ended in miscarriage at 10 weeks. My second pregnancy resulted in my daughter. She has some developmental delays specifically in speech and language. My third pregnancy ended at 15 weeks with an anencephalic baby. That pregnancy was terminated. My question is, could the miscarriage, my daughter's delays, and the anencephalic baby all be related to each other? Or are each of these instances random and just "bad luck?" Should I seek genetic testing before trying for another baby? See answer

  • If anencephaly occurred in a previous pregnancy, what are the chances of this condition affecting the next pregnancy if we take the recommended medication?  How long should the medication be taken before attempting another pregnancy? See answer

  • My mother had a baby with anencephaly. Does this increase the chances for me to have a baby with this condition? See answer


  1. NINDS Anencephaly Information Page. National Institute of Neurological Disorders and Stroke (NINDS). June 30, 2015; http://www.ninds.nih.gov/disorders/anencephaly/anencephaly.htm.
  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. November, 2014; http://ghr.nlm.nih.gov/condition/anencephaly.
  4. Robert G Best. Anencephaly. Medscape Reference. November, 2013; http://emedicine.medscape.com/article/1181570-overview.
  5. Diana W. Bianchi, Timothy M. Crombleholme, Mary E. D'Alton, Fergal D. Malone. Management of fetal conditions diagnosed by sonography. Fetology: Diagnosis and Management of the Fetal Patient, Second Edition. McGraw-Hill Companies; 2010; 77-82.