Anencephaly is a condition that affects the formation of the brain and the skull bones that surround the head at the time of birth. It results in the minimal development of the brain. There is no bony covering over the back of the head and there may also be missing bones around the front and sides of the head. This condition results when a structure called the neural tube fails to close during the first few weeks of embryonic development. Because anencephaly is caused by abnormalities of the neural tube, it is classified as a neural tube defect (NTD).
This type of neural tube defect occurs in about one in 10,000 pregnancies each year.
- If neural tube fails to close properly, the developing brain and spinal cord are exposed to the amniotic fluid that surrounds the foetus. The exposure causes the nervous system tissue to break down. As a result, people with anencephaly are missing large parts of the brain called the cerebrum and cerebellum.
- If all or part of the neural tube fails to close, leaving an opening, this is known as an open neural tube defect or ONTD. Anencephaly is one of the most common ONTDs. It happens to couples without a prior family history of these defects. ONTDs are a result from a combination of genes inherited from both parents, coupled with environmental factors. They are considered multifactorial traits, meaning many factors, both genetic and environmental, contribute to their occurrence. Once a child has been born with an ONTD in the family, the chance for an ONTD to happen again is increased by four to 10%.
Each child may experience symptoms differently. The symptoms of anencephaly may resemble other problems or medical conditions. These include:
- Absence of bony covering over the back of the head.
- Missing bones around the front and sides of the head.
- 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.
The diagnosis of anencephaly may be made during pregnancy or at birth by physical examination. Apart from ultrasounds and blood tests, other tests performed during pregnancy to evaluate the baby for anencephaly include:
- Alpha-fetoprotein: It is a protein produced by the foetus that is excreted into the amniotic fluid. Abnormal levels of this protein may indicate brain or spinal cord defects or chromosomal disorders.
- Amniocentesis: The test involves inserting a needle through the abdominal and uterine wall into the amniotic sac to retrieve a sample of amniotic fluid. This test is performed to determine chromosomal and genetic disorders and certain birth defects.
With regards to treatment of the newborn with anencephaly, there is no cure or standard medical treatment. Genetic counselling may be recommended by the doctor to discuss the risk of recurrence in a future pregnancy as well as vitamin therapy that can decrease the recurrence of ONTDs. To take further precautions, doctors advise to avoid smoking and drinking alcohol during pregnancy.