In the United States, anencephaly occurs in about 1 out of every 10,000 births. There are several forms of this condition, wherein the forebrain is absent. The forebrain is host to most of the higher functional areas in the mammalian brain. In the most extreme case of anencephaly, the so called holo-form, only the brain stem remains.

In MacLean's model of the brain, the term brain stem is used interchangeably with the term reptilian brain, to designate the most primitive parts of the central nervous system. Many are taught this model.

An anencephalic newborn (warning: graphic content)
("An anencephalic newborn", wikimedia, author: Almazi, license: public domain, DOR 27/09/2012)

From my layman's perspective I can't help but notice a reptilian likeness of the anencephalic newborn. Whilst it goes without saying that correlation doesn't equal causation, I would like to know what is known so far about the cause of this condition to yield this particular morphology (as seen in the picture)?

Perhaps someone (eventually) has even some evodevo insight to share as well?

  • $\begingroup$ youtube.com/watch?NR=1&feature=endscreen&v=WMlVNFpzKNI $\endgroup$ Commented Sep 27, 2012 at 18:06
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    $\begingroup$ the autonomous portions of the brain that control breathing and other physiological functions are lower in the brain. If the newborn is viable it just have just enough lower and back brain function to survive at least in utero. If a fetus expires in utero it does not go to full term as you probably know. $\endgroup$
    – shigeta
    Commented Sep 27, 2012 at 20:42
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    $\begingroup$ I think more should be discussion about induction factors, differentiation and transforming factors in the answers. Current answers do not answer this explicitly. $\endgroup$ Commented May 28, 2014 at 20:20

2 Answers 2


Know your databases! This is just the query fit for OMIM.


Anencephaly is considered an extreme form of neural tube defect (182940), which has been associated with variation in several genes. The entity described here is believed to show autosomal recessive inheritance.

The genes are those associated with neural tube effects, i.e., VANGL1, T, CCL1, and FUZ. See also folate-sensitive neural tube defects.


The folate evidence was so convincing that the US/Canada in the 1990s introduced folate supplementation in all bread, flour, and cereal products. Today, US/Canada have a lower incidence of NTD (neural tube defects) than Europe, where folate supplementation is completely left to one's choice (and if women actually care they take it too late).

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    $\begingroup$ good catch! I find the formation of the eyesockets striking. I am puzzled whether this is within the range of developmental plasticity as the result from different biomechanical forces due to craniosynostosis (premature skull fusion) OR if mutant genes (and/or pleiotrophies) are involved. OMIM unfortunately shows a practical lack of animal models. On a sidenote, the related spina bifida is known to interfere with the "eye" (opthalmic) devleopment.... $\endgroup$ Commented Sep 28, 2012 at 15:16

From what I've read and I know from my Biology classes, during the formation of the embryo a whole bunch of things may go wrong. In these cases, during the neurula stage, in which the brain is supposed to begin its development, something goes wrong while the neural tube is forming.

The causes? Some people argue that a lack of folic acid may lead to defective brain development. Studies seems to show that most factors don't affect the formation of the neural tube, which include age of the mother, occupation, and exposure to chemicals.


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