Topic Page: Anencephaly
Anencephaly is a disorder of the neural tube that results in a baby being born without a part or all of the brain and skull. During neural tube development, if the upper portion of the neural tube does not close all of the way, it results in portions of the brain not developing. This occurs because the developing brain is exposed to the amniotic fluid, which in utero can cause it and other nervous tissue to degenerate. The portions of the brain that are generally missing include the cerebrum and cerebellum. Fetuses with anencephaly usually are blind, deaf, unconscious, and cannot feel pain. Sometimes, the fetus retains the brainstem and so it is capable of breathing and may have other reflex actions. Generally, the skin and bone surrounding those missing portions also do not develop. Most babies born with anencephaly will die shortly after birth; approximately 1 in every 4,859 babies each year is born with anencephaly (CDC, 2013). Anencephaly is considered a neural tube defect.
The risk factors for anencephaly still are not completely known. The disease comes from a combination of complex environmental and genetic factors. One environmental factor that has been linked to cases of anencephaly is decreased amounts of folic acid in the pregnant mother. Folic acid deficiencies in pregnant women can lead to neural tube defects, including anencephaly. Studies have been performed indicating that the addition of 0.4 milligrams of folic acid each day to the diet of women of childbearing age can significantly reduce the probability of having a fetus develop anencephaly and other cephalic disorders. According to the CDC, there has been a 27 percent decline in pregnancies resulting in neural tube defects in the United States since folic acid has been used to fortify grains (CDC, 2013).
Anencephaly has also been linked to the MTHFR gene, which is one of many genes in which mutations can result in anencephaly. This gene is involved in making a protein product that is responsible for processing folic acid in the body. However, not all mutations in genes that are involved in folic acid processing result in anencephaly. Other environmental factors that have been linked to anencephaly include, but are not limited to, obesity, diabetes mellitus, exposure to high temperatures early in pregnancy (such as being in a hot tub), and the use of certain antiseizure medications during pregnancy.
Anencephaly can be diagnosed during pregnancy through ultrasound machines and alpha-fetoprotein (AFP) screening (detects levels of alpha-fetoprotein—a protein produced by the fetus that circulates in the mother's blood serum). Elevated AFP levels could indicate neural tube defects. Ultrasound examinations would need to be performed in order to determine if the elevated AFP levels were caused by a neural tube defect such as anencephaly. Detection of anencephaly can also occur after birth. There is no treatment or cure for anencephaly and generally, any child born with the condition will not live longer than a few days. Many fetuses affected by anencephaly will be aborted before they reach term.
See also Embryonic Development of the Nervous System; Hydrocephalus; Megalencephaly/Macrencephaly; Microcephaly; Neural Tube; Neural Tube—Illustration Activity
Related Articles
Full text Article Anencephaly
Anencephaly is a congenital disorder marked by the absence of the cerebral cortices. It belongs to a class of disorders that are termed neural tube
Full text Article Anencephaly
Definition, etiology and epidemiology This is a lethal congenital malformation of the posterior embryonic neural tube showing a small mass of amo
Full text Article Spina Bifida
This chapter includes text excerpted from “Spina Bifida,” Centers for Disease Control and Prevention (CDC), September 11, 2017.Spina bifida is a