Definition:

Anencephaly (ANPH1) is a congenital absence of a major portion of the brain, skull, and scalp. The primary abnormality is failure of cranial neurulation, the embryologic process that separates the precursors of the forebrain from amniotic fluid. Anencephaly shows a heterogeneous etiology, ranging from environmental to genetic causes. The autosomal recessive inheritance has been reported. Women with elevated levels of plasma homocysteine, low folate, or low vitamin B12 (cobalamin) are at an increased risk of having a child with neural tube defect (NTD). NTDs are the second most common type of birth defects and include anencephaly and open spina bifida [DS:H00262].