What causes anencephaly?
Anencephaly is a type of neural tube defect. Anencephaly occurs in about 1,000 to 2,000 births in the US each year. During pregnancy, the human brain and spine begin as a flat plate of cells, which rolls into a tube, called the neural tube. 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. This opening may be left exposed (80 percent of the time), or covered with bone or skin (20 percent of the time). Anencephaly and spina bifida are the most common ONTDs, while encephaloceles (where there is a protrusion of the brain or its coverings through the skull) are much rarer. Anencephaly occurs when the neural tube fails to close at the base of the skull, while spina bifida occurs when the neural tube fails to close somewhere along the spine. ONTDs happen to couples without a prior family history of these defects in over 95 percent of the cases. ONTDs result from a combination of genes inherited from both parents, coupl
