Anencephaly (Neural Tube Defect) Causes, Symptoms, Treatment, Prevention

Anencephaly (Neural Tube Defect) Causes, Symptoms, Treatment, Prevention


What is anencephaly?


Anencephaly, also known as “open skull,” is a birth defect in which the major parts of the brain, scalp, and skull of the fetus do not form completely as it is developing in the womb.

Anencephaly (Neural Tube Defect) Causes, Symptoms, Treatment, Prevention
Anencephaly (Neural Tube Defect) 

Anencephaly occurs when the neural tube, a narrow channel in the fetus that normally closes to form the spinal cord and brain, does not close properly between the third and fourth weeks of pregnancy. An infant who is born with anencephaly has some or most of the brain missing. These infants are unconscious, cannot feel, and are usually blind and deaf.

In many cases, some brain tissue may be exposed because parts of the skull are missing. Some infants may have a primitive brain stem at birth. They may seem to respond to sound or touch, but their reactions are involuntary and are caused by the action of the brain stem.

Anencephaly is a fatal condition. Infants with anencephaly are stillborn in about 75% of cases. Newborns who survive die within several hours, days, or weeks.

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What causes anencephaly?


The exact causes of anencephaly are unknown. A lack of folic acid (vitamin B9) before and during pregnancy may increase the chance of neural tube defects, such as anencephaly or spina bifida (a birth defect in which the spine is exposed). If a woman takes certain prescription drugs during pregnancy, such as drugs for diabetes, this may increase the risk of having an infant with anencephaly.

In about 90% of cases, the parents of an anencephalic infant do not have a family history of the disorder. However, if the parents have had a child who was born with anencephaly, they have a greater chance of having another baby with this condition. The recurrence rate for anencephaly is 4-5%, and rises to 10-13% if the parents have had two other children with anencephaly.

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.

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.

What are the symptoms of anencephaly?


The following are the most common symptoms of anencephaly. However, each child may experience symptoms differently. Symptoms may include:
  • absence of bony covering over the back of the head
  • missing bones around the front and sides of the head
  • folding of the ears
  • cleft palate - a condition in which the roof of the child's mouth does not completely close, leaving an opening that can extend into the nasal cavity.
  • congenital heart defects
  • some basic reflexes, but without the cerebrum, there can be no consciousness and the baby cannot survive
The symptoms of anencephaly may resemble other problems or medical conditions. Always consult your child's physician for a diagnosis.


How is anencephaly diagnosed?


Prenatal tests for anencephaly include the following:

  • Blood tests - may show high levels of alpha-fetoprotein, a protein produced by the immature liver cells of the fetus.
  • Amniocentesis - A small amount of fluid is withdrawn from the amniotic sac using a long needle that is inserted through the abdomen. The fluid can be analyzed to measure the levels of alpha-fetoprotein and acetylcholinerase; higher-than-normal levels are associated with neural tube defects, such as anencephaly.
  • Ultrasound - This is an imaging test that uses high-frequency sound waves and a computer to generate an image (sonogram) of the developing fetus. Abnormalities associated with anencephaly can be seen on the sonogram.
  • Fetal MRI - This is an imaging test that uses a magnet to generate an image of the developing fetus. The brain and its various structures can be visualized in more detail than the ultrasound alone.
Any of these procedures may be performed between the 14th and 18th weeks of pregnancy. The fetal MRI can be performed at any point of the pregnancy.

After a baby with anencephaly is born, the diagnosis is more apparent since the abnormalities of the skull can be easily seen. Bones around the front and sides of the head or the bony covering in the back of the head may be missing. Some brain tissue may be exposed when parts of the skull or scalp are missing.

How is anencephaly treated?


There is no treatment for anencephaly; instead, the child is provided with supportive care. The infant should be kept warm and any areas of the brain that are exposed must be protected. Sometimes a special bottle is used to help feed babies who may have difficulty swallowing fluids.

Experiencing the loss of a child can be very traumatic. Grief counseling services are available to help you cope with the loss of your child.

How can anencephaly be prevented?


Methods for preventing anencephaly include the following:

Proper nutrition


Eating nutritious foods and taking a vitamin supplement before and during pregnancy may help prevent neural tube birth defects. Getting enough folic acid (vitamin B9) is very important. Women of childbearing age should take a daily multivitamin supplement with at least 400 micrograms of folic acid, since most women do not obtain enough folic acid from food alone. 

Other good sources of folic acid include leafy green vegetables, dried beans, oranges, and orange juice. Some products are fortified with folic acid, including enriched flour, rice, bread, pasta, and cereals. In the case of folic acid, the synthetic form of the vitamin is more easily absorbed and utilized by the body than the form which occurs naturally in foods. The U.S. Food and Drug Administration requires that folic acid be added to all enriched cereal grain products. 

Folic acid supplements


Pregnant women who have previously given birth to an infant with a neural tube defect may have to take higher amounts of folic acid during pregnancy. Women should talk to their doctors about the recommended amount of folic acid. It is suggested that women who have had a previous pregnancy involving a neural tube defect should take 4 mg of folic acid, beginning one to two months before conception through their first trimester of pregnancy, under a doctor’s supervision.

How about future pregnancies?


Give yourself time to mourn for this baby and to recover from the trauma of his/her birth and death. Then, start taking 5mg of folic acid at least a month before you want to be pregnant again.

If you are a smoker, try to give up now, as smoking can inhibit the efficiency of folic acid. If you are on anti-epileptic drugs, speak to your neurologist about the effects folic acid may have on your medication. Once your pregnancy has been confirmed, ask your doctor to refer you for an early scan; if negative you will be re-scanned regularly up to the 20th week of the pregnancy.