A neural tube defect (NTD) that occurs when the cephalic (head) end of the neural tube fails to close, usually between the 23rd and 26th days of pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain, the largest part of the brain consisting mainly of the cerebrum, which is responsible for thinking and coordination. The remaining brain tissue is often exposed; it is not covered by bone or skin.
*Anencephaly facts medical author: Melissa Conrad Stöppler, MD
- Anencephaly is an example of a neural tube defect, a condition that results from an error in the first weeks of embryonic development.
- In anencephaly, the bones of the skull and brain do not develop properly. Babies with anencephaly are missing large areas of the brain and have an incomplete skull.
- Anencephaly affects about 1 out of every 1,000 pregnancies, but most cases end up as miscarriages. About 1 out of every 10,000 babies in the U.S. is born with anencephaly.
- In most cases, anencephaly is sporadic, meaning it does not run in families.
- Anencephaly is not compatible with life. Most babies with anencephaly are stillborn or die within days or hours of birth.
- The exact cause of anencephaly is unknown, but it is likely the result of an interaction among several genetic and environmental factors.
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).
What are the causes, signs, and symptoms of anencephaly?
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.