Which are the causes of Anencephaly?

TL;DR: Anencephaly is a severe neural tube defect (NTD) caused by the failure of the cephalic (head) end of the neural tube to close during the first month of embryonic development. The exact cause is generally multifactorial, involving a complex interplay between genetic predispositions and environmental influences rather than a single trigger.

What causes Anencephaly to occur?

Anencephaly occurs when the neural tube—the structure that eventually becomes the brain and spinal cord—fails to seal properly between the 23rd and 26th day after conception. Because the top of the tube remains open, the developing brain tissue is exposed to amniotic fluid, which causes the nervous tissue to degenerate. This process is not a result of anything the parent did or did not do, but rather a disruption in early fetal development.

Are there specific genetic or environmental risk factors?

While the precise cause is often unknown, research suggests that Anencephaly is multifactorial. This means it is likely caused by the combination of many small genetic variations and environmental exposures. Key factors identified by clinical researchers include:

• Folic Acid Deficiency: Low levels of folate (Vitamin B9) in the mother’s system are strongly linked to an increased risk of neural tube defects like Anencephaly.


• Maternal Health Conditions: Pre-existing conditions such as poorly controlled diabetes or obesity are known to raise the statistical risk.


• Medications: Certain anti-seizure medications (such as valproic acid) used during early pregnancy have been associated with a higher incidence of Anencephaly.


• Genetic Predisposition: Families who have had one pregnancy affected by Anencephaly have a slightly higher recurrence risk, usually cited between 2% and 5% in subsequent pregnancies.

Is the etiology of Anencephaly fully understood?

The etiology of Anencephaly remains an active area of study. Researchers are currently investigating how specific genes involved in folate metabolism interact with external environmental triggers. While we understand the anatomical mechanism—the failure of the neural tube to close—the "why" at the molecular level is still being mapped. Current research focuses on genomic sequencing to identify specific gene-environment interactions that contribute to Anencephaly.

Next steps

• Consult with a clinical geneticist or a maternal-fetal medicine specialist to discuss recurrence risks if you have been personally affected.


• Connect with the 31 members of the DiseaseMaps.org community who have shared their experiences to find peer support.


• Speak with your primary care physician about recommended folic acid supplementation if you are planning a future pregnancy.

Medical disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment; always seek the advice of a qualified healthcare provider.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Anencephaly Overview.


• Orphanet: Neural tube defects, including Anencephaly.


• Centers for Disease Control and Prevention (CDC): Facts about Anencephaly.


• OMIM (Online Mendelian Inheritance in Man): Anencephaly database.