Question: What is (are) Anencephaly ?
Answer: Anencephaly is a type of neural tube defect characterized by abnormal development of the brain and the bones of the skull. The neural tube is a narrow channel that normally folds and closes between the 3rd and 4th weeks of pregnancy, forming the brain and spinal cord of the embryo. Anencephaly occurs when the 'cephalic' or head end of the neural tube fails to close, causing the absence of a major portion of the brain, skull, and scalp. Infants with this disorder are born without a forebrain (the front part of the brain) and a cerebrum (the thinking and coordinating part of the brain). The remaining brain tissue is often exposed (not covered by bone or skin). Affected babies are usually blind, deaf, unconscious, and unable to feel pain. Almost all babies with anencephaly die before birth, although some may survive a few hours or a few days after birth. Anencephaly is likely caused by an interaction between genetic and environmental factors, many of which remain unknown.
Source: GARD

Question: What causes Anencephaly ?
Answer: What causes anencephaly? The underlying cause of anencephaly is not fully understood. Like other forms of neural tube defects (NTDs), anencephaly is likely caused by the interaction of multiple genes and environmental factors, many of which remain unknown. Variations in many genes may influence the risk of developing anencephaly. The best-studied gene thus far is the MTHFR gene, which gives the body instructions to make a protein used to process the vitamin folate (also called vitamin B9). A deficiency of folate is a known risk factor for NTDs. Other genes involved in folate processing, and the development of the neural tube, may also affect the risk. Researchers have also looked at environmental factors that could contribute to the risk of anencephaly. Folate appears to play a significant role, and studies have shown that taking folic acid (a form of folate), before getting pregnant and very early in pregnancy, significantly reduces the risk to have a baby with a NTD. Other possible maternal risk factors for anencephaly include diabetes mellitus; obesity; exposure to high heat (such as a fever or use of a hot tub or sauna) in early pregnancy; and the use of certain anti-seizure medications during pregnancy.
Source: GARD