Abnormal development during embryonic life of the neural tube producing congenital malformations of the nervous system due to closure failure of the neural tube.

The structure gives rise to the central nervous system (the brain and spinal cord), and failure to close results in anencephaly (absence of the brain) and spina bifida or meningomyelocele (open spine with exposure and protusion of the spinal cord).

The risk of neural tube defects can be decreased by the mother taking folic acid during pregnancy.