Description:
Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development. It is a cephalic disorder that results from a neural tube defect that occurs when the rostral (head) end of the neural tube fails to close, usually between the 23rd and 26th day following conception. Strictly speaking, the Greek term translates as “without a brain” (or totally lacking the inside part of the head), but it is accepted that children born with this disorder usually only lack a telencephalon, the largest part of the brain consisting mainly of the cerebral hemispheres, including the neocortex, which is responsible for cognition. The remaining structure is usually covered only by a thin layer of membrane—skin, bone, meninges, etc. are all lacking. The neural tube is a layer of cells that ultimately develops into the brain and spinal cord. Because anencephaly is caused by abnormalities of the neural tube, it is classified as a neural tube defect (NTD). With very few exceptions, infants with this disorder do not survive longer than a few hours or possibly days after their birth.
Symptoms:
The National Institute of Neurological Disorders and Stroke (NINDS) describes the presentation of this condition as follows: “A baby born with anencephaly is usually blind, deaf, unaware of its surroundings and unable to feel pain. Although some individuals with anencephaly may be born with a main brain stem, the lack of a functioning cerebrum permanently rules out the possibility of ever gaining awareness of their surroundings. Reflex actions such as breathing and responses to sound or touch may occur.”
Due to the presence of the brainstem, children with anencephaly have almost all the primitive reflexes of a newborn, responding to auditory, vestibular and painful stimuli. This means that the child can move, smile, suckle and breathe without the aid of devices.
Causes:
The cause of anencephaly is disputed by medical professionals and researchers.
Folic acid has been shown to be important in neural tube formation since at least 1991, and as a subtype of neural tube defect, folic acid may play a role in anencephaly. Studies have shown that the addition of folic acid to the diet of women of child-bearing age may significantly reduce, although not eliminate, the incidence of neural tube defects. Therefore, it is recommended that all women of child-bearing age consume 0.4 mg of folic acid daily, especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%. It is not advisable to wait until pregnancy has begun, since, by the time a woman knows she is pregnant, the critical time for the formation of a neural tube defect has usually already passed. A physician may prescribe even higher dosages of folic acid (5 mg/day) for women having had a previous pregnancy with a neural tube defect.
In general, neural tube defects do not follow direct patterns of heredity, though there is some indirect evidence of inheritance, and recent animal models indicate a possible association with deficiencies of the transcription factor TEAD2. Studies show that a woman who has had one child with a neural tube defect such as anencephaly has about a 3% risk of having another child with a neural tube defect, as opposed to the background rate of 0.1% occurrence in the population at large. Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing.
An infant with anencephaly and acrania
It is known that people taking certain anticonvulsants and people with insulin-dependent diabetes have a higher risk of having a child with a neural tube defect.
Relation to genetic ciliopathy:
Until recently, medical literature did not indicate a connection among many genetic disorders, both genetic syndromes and genetic diseases, that are now being found to be related. As a result of new genetic research, some of these are, in fact, highly related in their root cause despite the widely varying set of medical symptoms that are clinically visible in the disorders. Anencephaly is one such disease, part of an emerging class of diseases called ciliopathies. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell, organelles present in many cellular types throughout the human body. The cilia defects adversely affect “numerous critical developmental signaling pathways” essential to cellular development and, thus, offer a plausible hypothesis for the often multi-symptom nature of a large set of syndromes and diseases. Known ciliopathies include primary ciliary dyskinesia, Bardet–Biedl syndrome, polycystic kidney and liver disease, nephronophthisis, Alström syndrome, Meckel–Gruber syndrome, and some forms of retinal degeneration.
Research:
Some genetic research has been conducted to determine the causes of anencephaly. It has been found that cartilage homeoprotein (CART1) is selectively expressed in chondrocytes (cartilage cells). The CART1 gene to chromosome 12q21.3–q22 has been mapped. Also, it has been found that mice homozygous for deficiency in the Cart1 gene manifested acrania and meroanencephaly, and prenatal treatment with folic acid will suppress acrania and meroanencephaly in the Cart1-deficient mutants
Diagnosis:
Anencephaly can often be diagnosed before birth through an ultrasound examination. The maternal serum alpha-fetoprotein (AFP screening) and detailed fetal ultrasound can be useful for screening for neural tube defects such as spina bifida or anencephaly.
Meroanencephaly:
Meroanencephaly is a rare form of anencephaly characterized by malformed cranial bones, a median cranial defect, and a cranial protrusion called area cerebrovasculosa. Area cerebrovasculosa is a section of abnormal, spongy, vascular tissue admixed with glial tissue ranging from simply a membrane to a large mass of connective tissue, hemorrhagic vascular channels, glial nodules, and disorganized choroid plexuses.
Holoprosencephaly:
The most common type of anencephaly, where the brain has entirely failed to form, except for the brain stem. Infants rarely survive more than one day after birth with holoanencephaly.
Craniorachischisis:
The most severe type of anencephaly where area cerebrovasculosa and area medullovasculosa fill both cranial defects and the spinal column. Craniorachischisis is characterized by anencephaly accompanied by bony defects in the spine and the exposure of neural tissue as the vault of the skull fails to form. Craniorachischisis occurs in about 1 of every 1000 live births, but various physical and chemical tests can detect neural tube closure during early pregnancy.
Treatment:
There is no cure or standard treatment for anencephaly.
Prognosis:
Prognosis is extremely poor, as many anencephalic fetuses do not survive birth and infants that are not stillborn will usually die within a few hours or days after birth from cardiorespiratory arrest.
In almost all cases, anencephalic infants are not aggressively resuscitated because there is no chance of the infants ever achieving a conscious existence. Instead, the usual clinical practice is to offer hydration, nutrition, and comfort measures and to “let nature take its course”. Artificial ventilation, surgery (to fix any co-existing congenital defects), and drug therapy (such as antibiotics) are usually regarded as futile efforts. Some clinicians and medical ethicists view even the provision of nutrition and hydration as medically futile
Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.
Resources:
https://en.wikipedia.org/wiki/Anencephaly
https://www.medicinenet.com/anencephaly/article.htm
