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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"<p>Anencephaly is a complex condition that is likely caused by the interaction of multiple genetic and environmental factors. Some of these factors have been identified, but many remain unknown.</p><p>Changes in dozens of genes in individuals with anencephaly and in their mothers may influence the risk of developing this type of neural tube defect. The best-studied of these genes is MTHFR, which provides instructions for making a protein that is involved in processing the vitamin folate (also called vitamin B9). While a shortage (deficiency) of this vitamin is an established risk factor for neural tube defects, there are many factors that can contribute to folate deficiency. Changes in other genes related to folate processing and genes involved in the development of the neural tube have also been studied as potential risk factors for anencephaly. However, no genes appear to play a major role in causing the condition.</p><p>Researchers have also examined environmental factors that could contribute to the risk of anencephaly. Folate deficiency plays a significant role. Studies have shown that women who take supplements containing folic acid (the synthetic form of folate) before they get pregnant and very early in their pregnancy are significantly less likely to have a baby with a neural tube defect, including anencephaly. 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. However, it is unclear how these factors may influence the risk of anencephaly.</p><p class=\"section-source\"><a href=\"https://medlineplus.gov/genetics/condition/anencephaly/#causes\">MedlinePlus Genetics: Causes</a></p>","key":"forms","title":"What causes Anencephaly?"},{"bodyHtml":"<p>Because the neural tube fails to close properly, the developing brain and spinal cord are exposed to the amniotic fluid that surrounds the fetus in the womb. This exposure causes the nervous system tissue to break down (degenerate). As a result, people with anencephaly are missing large parts of the brain called the cerebrum and cerebellum. These brain regions are necessary for thinking, hearing, vision, emotion, and coordinating movement. The bones of the skull are also missing or incompletely formed.</p><p>Because these nervous system abnormalities are so severe, almost all babies with anencephaly die before birth or within a few hours or days after birth.</p><p class=\"section-source\">Source: <a href=\"https://medlineplus.gov/genetics/condition/anencephaly\">MedlinePlus Genetics</a></p>","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"anencephaly","sourceDocuments":[{"name":"Anencephaly","reviewed":"2014-11","sections":{"causes":{"fetchedAt":"2026-10-20T20:19:23.354465+00:00","label":"Causes","pageSha256":"55353e92c962dc1daa0430fe7e2e17274ff7e0642bcaab3c2d45a07e8948e386","sourceUrl":"https://medlineplus.gov/genetics/condition/anencephaly/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/anencephaly"}],"sourceNote":"MedlinePlus descriptions and Causes; original HPO annotations.","takeawayHtml":"Cause explanations are from MedlinePlus Genetics. Feature values below retain their original sources and patient groups.","title":"Anencephaly"},"schemaVersion":1}