What Causes Anencephaly?

Genetic and Environmental Factors May Cause Neural Tube Defects

woman touching her abdomen after hearing she is carrying a baby with anencephaly
What are the causes of anencephaly?. Mustafa Arican / Getty Images

Anencephaly is a type of birth defect in which crucial parts of the baby's brain and skull fail to form. Unfortunately, babies affected by anencephaly frequently are stillborn or die at birth. Even if born alive, babies with anencephaly always die within a few days of birth. There is no treatment that can change the prognosis.

Understanding Neural Tube Defects

Anencephaly is a type of neural tube defect (NTD), which are birth defects involving the brain, spine or spinal cord.

 These are conditions in which the developing neural tube does not close properly during the baby's development very early in the first trimester. Neural tube defects have a wide range of severity, from only minor health concerns to being 100 percent fatal. 

On the severe range of that spectrum is anencephaly, one of the most devastating diagnoses expectant parents can receive during pregnancy. Unfortunately, babies with anencephaly can never gain consciousness or carry out the physical functions of life because they are missing important parts of their brain. Because the skull is also affected by the disorder, babies with anencephaly are usually physically deformed and parts of their brain may be exposed. 

How Anencephaly Is Diagnosed

Anencephaly is often apparent on an ultrasound by the second trimester.

The first clue about the diagnosis might be abnormalities in the alphafetoprotein (AFP) blood test.

The AFP test can identify 80 to 90 percent of babies who have a neural tube defect.

Amniocentesis may be used in the diagnosis as well. An anencephaly diagnosis is unlikely to be a false positive.

Causes of Anencephaly

Anencephaly appears to be caused by a combination of genetic and environmental factors.

The interplay of these factors disrupts the closure of the neural tube, which occurs between the third and fourth week of pregnancy. The specifics of the factors at work in anencephaly and other neural tube defects are still not well understood. Though we don't know the precise causes of anencephaly, some risk factors have been identified, including an inadequate intake of folic acid.

Folic Acid and Neural Tube Defects

There is evidence that having an adequate intake of folic acid before conception will reduce the risk of having a baby affected by any neural tube defect, although the reasons for this are not well understood. This is why doctors advise all women of childbearing age to take folic acid supplements and eat folate-rich foods on a regular basis. Don't wait until you're already pregnant. Many obstetricians recommend beginning a folic acid supplement at least three months prior to becoming pregnant.

That said, anencephaly can occur even when moms eat a perfect diet, so it cannot necessarily be prevented and it is definitely not anyone's fault when it does occur. In fact, a 2015 study evaluating the prevalence of neural tube defects such as anencephaly in Europe, found that there has not been any reduction in the incidence of these defects, despite widespread recommendations to increase folic acid which have been in place for several decades.

On the other hand, both the occurrence and the severity of spinal neural tube defects (spina bifida) have appeared to decrease in regions of the world in which food is regularly supplement with folic acid.

Genetic Mutations

We are just beginning to learn of gene mutations which may increase the risk of anencephaly. Talking to a genetic counselor may help you determine if inheritance may have played a role. Yet that said, a hereditary pattern may only mean that there is a predisposition for neural tube defects, but not that these changes cause neural tube defects.

Other Risk Factors

Other factors which may play a role in the development of anencephaly include socioeconomic status, educational status, maternal age, and environmental factors in addition to folic acid.

There is currently an ongoing investigation in Washington state evaluating a cluster of babies with anencephaly and looking for possible causes, whether these may be genetic (related to variants in the folic acid pathway), exposure to environmental or occupational toxins, and more.

The Risk of Recurrence

Parents who have a child with anencephaly may have a four to ten percent risk of having a child affected by neural tube defects in a future pregnancy, although the specific neural tube defect might not be anencephaly. Doctors may advise taking high doses of folic acid before conceiving again and may recommend that the couple works with a genetic counselor as well.

Deciding What to Do After a Diagnosis

The decision of what to do after an anencephaly diagnosis can be heart-wrenching.

Many parents decide to terminate the pregnancy after receiving a diagnosis of anencephaly, knowing that there is zero chance that the baby will live. Ending the pregnancy can help parents to move forward and begin the grieving process. Neural tubes are one of the reasons for which pregnancy may be terminated for medical reasons.

Other parents may have strict religious or other personal beliefs against abortion, and they may choose to carry the pregnancy to term with the full knowledge that the baby will not live more than a few days at most.

If you are facing this tragic choice, be sure to take your time making the decision and do what feels right for you and your partner. Give yourself room to grieve the loss of the baby.

Coping When Your Baby is Diagnosed with Anencepaly

It's OK to be angry, sad, or to experience any other feelings. Your hospital may have grief counselors available, and there are numerous support groups available on the Internet that target couples dealing with an anencephaly diagnosis. Support groups for anencephaly tend to be geared toward a specific course of action for dealing with the pregnancy—whether that means terminating the pregnancy or carrying it to term—so you may need to look around to find the one which best fits your needs.

For Family and Friends of a Couple Facing Anencephaly

If you are a family member or a friend of someone facing a pregnancy with anencephaly, your loved one will need all the support you can give. Any form of loss, whether that means miscarriage, stillbrith, or the death of a newborn is difficult, but anencephaly adds a further dimension. Hearing about folic acid and such can lead parents to blame themselves, and the possible approaches are emotion laden, like trying to make the choice between taking a right turn into great white shark infested waters, or a left turn into a crocodile filled river.

As a very helpful hint, try NOT to bring up the possible causes of the anencephaly with your loved one. These questions are important, but should be left with those who are researching the causes, not the grieving mother. You can be sure that your loved ones have already tortured themselves enough with the possible causes. On the same hand, please do not bring up topics such as the risk that a neural tube defect may happen again. Your loved ones are grieving, and need this time to cope with their very real grief today.

Finally, even if you would make a different choice if this was your own pregnancy, for example, if you would choose to go to term and your loved one is choosing to terminate, or if you would terminate but your loved one is choosing to go to term, remember that this is not your decision to make. And, hopefully, you will never need to make this decision for yourself, for, as we well know, people often state they would choose one treatment when looking at a condition from afar, but choose a different approach when faced with the same decision themselves in real life. Your loved ones need to make the choice that is best for them, not someone else. Regardless of their choice they need your full support and caring.

Sources:

Barron, S. Anencephaly: An Ongoing Investigation in Washington State. American Journal of Nursing. 2016. 116(3):60-6.

Khoshnood, B., Loane, M., de Walle, H. et al. Long Term Trends in Prevalence of Neural Tube Defects in Europe: Population Based Study. BMJ. 2015. 351:h5949.

Laharwal, M., Sarmast, A., Ramzan, A. et al. Epidemiology of the Neural Tube Defects in Kashmir Valley. Journal of Pediatric Neurosciences. 2016. 11(3):213-218.

Singh, N., Kumble Bhat, V., Tiwari, A. et al. A Homozygous Mutation in TRIM36 Causes Autosomal Recessive Anencephaly in an Indian Family. Human Molecular Genetics. 2017 Jan 13. (Epub ahead of print).

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