Anencephaly

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Anencephaly
Anencephaly-web.jpg
Illustration of an anencephalic fetus
Specialty Medical genetics; pediatrics
Symptoms Absence of the cerebrum and cerebellum
Risk factors Folic acid deficiency
PreventionMother taking enough folic acid
Prognosis Death typically occurs within hours to days after birth.
Frequency1 in 4600 in the U.S.

Anencephaly is the absence of a major portion of the brain, skull, and scalp that occurs during embryonic development. [1] 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. [2] 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, [3] 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. [4] With very few exceptions, [5] infants with this disorder do not survive longer than a few hours or days after birth.

Contents

Signs and 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." [4]


Anencephaly side.jpg
A side view of an anencephalic fetus
Anencephaly front.jpg
A front view of an anencephalic fetus
Babygram.jpg
X-ray of an anencephalic stillborn baby

Causes

Folic acid has been shown to be important in neural tube formation since at least 1991, [6] [7] 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, [4] especially those attempting to conceive or who may possibly conceive, as this can reduce the risk to 0.03%. [8] 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. [8]

Neural tube defects can follow patterns of heredity, with direct evidence of autosomal recessive inheritance. [9] As reported by Bruno Reversade and colleagues, the homozygous inactivation of the NUAK2 kinase leads to anencephaly in humans. [10] Animal models indicate a possible association with deficiencies of the transcription factor TEAD2. [11] 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, [12] as opposed to the background rate of 0.1% occurrence in the population at large. [13] Genetic counseling is usually offered to women at a higher risk of having a child with a neural tube defect to discuss available testing. [14]

An infant with anencephaly and acrania Anencefalia.jpg
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. [15]

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. [16]

Diagnosis

Ultrasound image of fetus with anencephaly Ultrasound Scan ND 066.jpg
Ultrasound image of fetus with anencephaly

Anencephaly can often be diagnosed before birth through an ultrasound examination. The maternal serum alpha-fetoprotein (AFP screening) [17] and detailed fetal ultrasound [18] 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. [19]

Holoanencephaly

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. [19]

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. [19] [20] Craniorachischisis occurs in about 1 of every 1000 live births, but various physical and chemical tests can detect neural tube closure during early pregnancy. [21]

Prognosis

There is no cure or standard treatment for anencephaly. 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. [4]

Epidemiology

In the United States, anencephaly occurs in about 1 out of every 4600 births. [22] Rates may be higher among Africans with rates in Nigeria estimated at 3 per 10,000 in 1990 while rates in Ghana estimated at 8 per 10,000 in 1992. [23] As of 2005, rates in China were estimated at 5 per 10,000. [23]

A high anencephaly rate of 19.7 per 10,000 live births was found in 1990/1991 in Brownsville, Texas. A cluster of cases made national headlines [24] and prompted a public health investigation and the Texas Neural Tube Defect Project. It was found, that neural tube defects in general, including spina bifida, and encephalocele had been occurring in Mexican-American women undetected for years in the area. [25] Subsequently, multiple risk factors were found, foremost folic acid deficiency, low serum vitamin B12, high serum homocysteine levels, and obesity independently contributed to risk. Increasing dietary folate intake had a protective effect. [26]

Research has suggested that, overall, female babies are more likely to be affected by the disorder. [27]

Ethical issues

Organ donation

One issue concerning anencephalic newborns is organ donation. Initial legal guidance came from the case of Baby Theresa in 1992, in which the boundaries of organ donation were tested for the first time. [28] Infant organs are scarce, and the high demand for pediatric organ transplants poses a major public health issue. In 1999, it was found that for American children under the age of two who are waiting for a transplant, 30–50% die before an organ becomes available. [28]

Within the medical community, the main ethical issues with organ donation are a misdiagnosis of anencephaly, the slippery slope argument, that anencephalic neonates would rarely be a source of organs, and that it would undermine confidence in organ transplantation. [29] Slippery slope concerns are a major issue in personhood debates, across the board. In regards to anencephaly, those who oppose organ donation argue that it could open the door for involuntary organ donors such as an elderly person with severe dementia. Another point of contention is the number of children who would actually benefit. There are discrepancies in statistics; however, it is known that most anencephalic children are stillborn. [29]

Proposals have been made to bypass the legal and ethical issues surrounding organ donation. These include waiting for death to occur before procuring organs, expanding the definition of death, creating a special legal category for anencephalic infants, and defining them as non-persons. [30]

In the United Kingdom, a child born with anencephaly was reported as the country's youngest organ donor. Teddy Houlston was diagnosed as anencephalic at 12 weeks of gestation. His parents, Jess Evans and Mike Houlston, decided against abortion and instead proposed organ donation. Teddy was born on 22 April 2014, in Cardiff, Wales, and lived for 100 minutes, after which his heart and kidneys were removed. His kidneys were later transplanted into an adult in Leeds. Teddy's twin, Noah, was born healthy. [31]

Brain death

There are four different concepts used to determine brain death: failure of heart, failure of lungs, whole brain death, and neocortical death.[ citation needed ]

Neocortical death, similar to a persistent vegetative state (PVS), involves loss of cognitive functioning of the brain. A proposal by law professor David Randolph Smith, [32] in an attempt to prove that neocortical death should legally be treated the same as brain death, involved PET scans to determine the similarities. However, this proposal has been criticized on the basis that confirming neocortical death by PET scan may risk indeterminacy. [33]

Pregnancy termination

Anencephaly can be diagnosed before delivery with a high degree of accuracy. Although anencephaly is a fatal condition, the option of abortion is dependent on the abortion laws in the state. [34] According to a 2013 report, 26% of the world's population reside in a country where abortion is generally prohibited. [34] [35] In 2012, Brazil extended the right of abortion to mothers with anencephalic fetuses. This decision is, however, receiving much disapproval by several religious groups. [36]

The case of baby Theresa was the beginning of the ethical debate over anencephalic infant organ donation. [28] The story of baby Theresa remains a focus of basic moral philosophy. Baby Theresa was born with anencephaly in 1992. Her parents, knowing that their child was going to die, requested that her organs be given for transplantation. Although her physicians agreed, Florida law prohibited the infant's organs from being removed while she was still alive. By the time she died nine days after birth, her organs had deteriorated past the point of being viable. [37]

United States uniform acts

The Uniform Determination of Death Act (UDDA) is a model bill, adopted by many US states, stating that an individual who has sustained either 1) irreversible cessation of circulatory and respiratory functions or 2) irreversible cessation of all functions of the entire brain, including the brain stem, is dead. This bill was a result of much debate over the definition of death and is applicable to the debate over anencephaly. A related bill, the Uniform Anatomical Gift Act (UAGA), grants individuals and, after death, their family members the right to decide whether or not to donate organs. Because it is against the law for any person to pay money for an organ, the person in need of an organ transplant must rely on a volunteer. [34]

There have been two state bills that proposed to change current laws regarding death and organ donation. California Senate Bill 2018 proposed to amend the UDDA to define anencephalic infants as already dead, while New Jersey Assembly Bill 3367 proposed to allow anencephalic infants to be organ sources even if they are not dead. [34] [38]

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. [39] [40]

See also

Related Research Articles

<span class="mw-page-title-main">Folate</span> Vitamin B9; nutrient essential for DNA synthesis

Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and storage. Folate is required for the body to make DNA and RNA and metabolise amino acids necessary for cell division and maturation of blood cells. As the human body cannot make folate, it is required in the diet, making it an essential nutrient. It occurs naturally in many foods. The recommended adult daily intake of folate in the U.S. is 400 micrograms from foods or dietary supplements.

<span class="mw-page-title-main">Spina bifida</span> Birth defect of the spinal cord

Spina bifida is a birth defect in which there is incomplete closing of the spine and the membranes around the spinal cord during early development in pregnancy. There are three main types: spina bifida occulta, meningocele and myelomeningocele. Meningocele and myelomeningocele may be grouped as spina bifida cystica. The most common location is the lower back, but in rare cases it may be in the middle back or neck.

Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology caused by teratogens. Teratogens are substances that may cause non-heritable birth defects via a toxic effect on an embryo or fetus. Defects include malformations, disruptions, deformations, and dysplasia that may cause stunted growth, delayed mental development, or other congenital disorders that lack structural malformations. The related term developmental toxicity includes all manifestations of abnormal development that are caused by environmental insult. The extent to which teratogens will impact an embryo is dependent on several factors, such as how long the embryo has been exposed, the stage of development the embryo was in when exposed, the genetic makeup of the embryo, and the transfer rate of the teratogen.

<span class="mw-page-title-main">Iniencephaly</span> Rare neural tube defect characterised by fusion of the occiput with the spine

Iniencephaly is a rare type of cephalic disorder characterised by three common characteristics: a defect to the occipital bone, spina bifida of the cervical vertebrae and retroflexion of the head on the cervical spine. Stillbirth is the most common outcome, with a few rare examples of live birth, after which death invariably occurs within a short time.

<span class="mw-page-title-main">Microcephaly</span> Condition in which the head is small due to an underdeveloped brain

Microcephaly is a medical condition involving a smaller-than-normal head. Microcephaly may be present at birth or it may develop in the first few years of life. Brain development is often affected; people with this disorder often have an intellectual disability, poor motor function, poor speech, abnormal facial features, seizures and dwarfism.

Exencephaly is a type of cephalic disorder wherein the brain is located outside of the skull. This condition is usually found in embryos as an early stage of anencephaly. As an exencephalic pregnancy progresses, the neural tissue gradually degenerates.

<span class="mw-page-title-main">Birth defect</span> Condition present at birth regardless of cause

A birth defect is an abnormal condition that is present at birth, regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth defects are divided into two main types: structural disorders in which problems are seen with the shape of a body part and functional disorders in which problems exist with how a body part works. Functional disorders include metabolic and degenerative disorders. Some birth defects include both structural and functional disorders.

<span class="mw-page-title-main">Prenatal testing</span> Testing for diseases or conditions in a fetus

Prenatal testing is a tool that can be used to detect some birth defects at various stages prior to birth. Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible. These may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts or as early in gestation as practicable. Screening can detect problems such as neural tube defects, chromosome abnormalities, and gene mutations that would lead to genetic disorders and birth defects, such as spina bifida, cleft palate, Down syndrome, trisomy 18, Tay–Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile X syndrome. Some tests are designed to discover problems which primarily affect the health of the mother, such as PAPP-A to detect pre-eclampsia or glucose tolerance tests to diagnose gestational diabetes. Screening can also detect anatomical defects such as hydrocephalus, anencephaly, heart defects, and amniotic band syndrome.

<span class="mw-page-title-main">Encephalocele</span> Neural tube defect in which the brain protrudes out of the skull

Encephalocele is a neural tube defect characterized by sac-like protrusions of the brain and the membranes that cover it through openings in the skull. These defects are caused by failure of the neural tube to close completely during fetal development. Encephaloceles cause a groove down the middle of the skull, or between the forehead and nose, or on the back side of the skull. The severity of encephalocele varies, depending on its location.

Neurodevelopmental disorders are a group of mental conditions affecting the development of the nervous system, which includes the brain and spinal cord. According to the American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, (DSM-5) published in 2013, these conditions generally appear in early childhood, usually before children start school, and can persist into adulthood. The key characteristic of all these disorders is that they negatively impact a person's functioning in one or more domains of life depending on the disorder and deficits it has caused. All of these disorders and their levels of impairment exist on a spectrum, and affected individuals can experience varying degrees of symptoms and deficits, despite having the same diagnosis.

<span class="mw-page-title-main">Neural tube defect</span> Group of birth defects of the brain or spinal cord

Neural tube defects (NTDs) are a group of birth defects in which an opening in the spine or cranium remains from early in human development. In the third week of pregnancy called gastrulation, specialized cells on the dorsal side of the embryo begin to change shape and form the neural tube. When the neural tube does not close completely, an NTD develops.

<span class="mw-page-title-main">Otocephaly</span> Congenital first branchial arch defect

Otocephaly, also known as agnathia–otocephaly complex, is a very rare and lethal cephalic disorder characterized by the absence of the mandible (agnathia), with the ears fused together just below the chin (synotia). It is caused by a disruption to the development of the first branchial arch. It occurs in every 1 in 70,000 embryos.

<span class="mw-page-title-main">Folate deficiency</span> Abnormally low level of folate (vitamin B9) in the body

Folate deficiency, also known as vitamin B9 deficiency, is a low level of folate and derivatives in the body. This may result in megaloblastic anemia in which red blood cells become abnormally large, and folate deficiency anemia is the term given for this medical condition. Signs of folate deficiency are often subtle. Symptoms may include fatigue, heart palpitations, shortness of breath, feeling faint, open sores on the tongue, loss of appetite, changes in the color of the skin or hair, irritability, and behavioral changes. Temporary reversible infertility may occur. Folate deficiency anemia during pregnancy may give rise to the birth of low weight birth premature infants and infants with neural tube defects.

<span class="mw-page-title-main">Meckel–Gruber syndrome</span> Medical condition

Meckel-Gruber syndrome is a rare, lethal ciliopathic genetic disorder, characterized by renal cystic dysplasia, central nervous system malformations, polydactyly (postaxial), hepatic developmental defects, and pulmonary hypoplasia due to oligohydramnios. Meckel–Gruber syndrome is named for Johann Meckel and Georg Gruber.

<span class="mw-page-title-main">Central nervous system disease</span> Disease of the brain or spinal cord

Central nervous system diseases or central nervous system disorders are a group of neurological disorders that affect the structure or function of the brain or spinal cord, which collectively form the central nervous system (CNS). These disorders may be caused by such things as infection, injury, blood clots, age related degeneration, cancer, autoimmune disfunction, and birth defects. The symptoms vary widely, as do the treatments.

<span class="mw-page-title-main">Ciliopathy</span> Genetic disease resulting in abnormal formation or function of cilia

A ciliopathy is any genetic disorder that affects the cellular cilia or the cilia anchoring structures, the basal bodies, or ciliary function. Primary cilia are important in guiding the process of development, so abnormal ciliary function while an embryo is developing can lead to a set of malformations that can occur regardless of the particular genetic problem. The similarity of the clinical features of these developmental disorders means that they form a recognizable cluster of syndromes, loosely attributed to abnormal ciliary function and hence called ciliopathies. Regardless of the actual genetic cause, it is clustering of a set of characteristic physiological features which define whether a syndrome is a ciliopathy.

<span class="mw-page-title-main">Rachischisis</span> Neural tube defect in which the spinal cord is exposed

Rachischisis is a developmental birth defect involving the neural tube. This anomaly occurs in utero, when the posterior neuropore of the neural tube fails to close by the 27th intrauterine day. As a consequence the vertebrae overlying the open portion of the spinal cord do not fully form and remain unfused and open, leaving the spinal cord exposed. Patients with rachischisis have motor and sensory deficits, chronic infections, and disturbances in bladder function. This defect often occurs with anencephaly.

Women should speak to their doctor or healthcare professional before starting or stopping any medications while pregnant. Non-essential drugs and medications should be avoided while pregnant. Tobacco, alcohol, marijuana, and illicit drug use while pregnant may be dangerous for the unborn baby and may lead to severe health problems and/or birth defects. Even small amounts of alcohol, tobacco, and marijuana have not been proven to be safe when taken while pregnant. In some cases, for example, if the mother has epilepsy or diabetes, the risk of stopping a medication may be worse than risks associated with taking the medication while pregnant. The mother's healthcare professional will help make these decisions about the safest way to protect the health of both the mother and unborn child. In addition to medications and substances, some dietary supplements are important for a healthy pregnancy, however, others may cause harm to the unborn child.

<span class="mw-page-title-main">Developmental toxicity</span>

Developmental toxicity is any developmental malformation that is caused by the toxicity of a chemical or pathogen. It is the structural or functional alteration, reversible or irreversible, which interferes with homeostasis, normal growth, differentiation, development or behavior. Developmental toxicity is caused by environmental insult, which includes drugs, alcohol, diet, toxic chemicals, and physical factors.

<span class="mw-page-title-main">Mitochondrial DNA depletion syndrome</span> Medical condition

Mitochondrial DNA depletion syndrome, or Alper's disease, is any of a group of autosomal recessive disorders that cause a significant drop in mitochondrial DNA in affected tissues. Symptoms can be any combination of myopathic, hepatopathic, or encephalomyopathic. These syndromes affect tissue in the muscle, liver, or both the muscle and brain, respectively. The condition is typically fatal in infancy and early childhood, though some have survived to their teenage years with the myopathic variant and some have survived into adulthood with the SUCLA2 encephalomyopathic variant. There is currently no curative treatment for any form of MDDS, though some preliminary treatments have shown a reduction in symptoms.

References

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  32. ↑ "Archived copy" (PDF). Archived (PDF) from the original on 2013-10-15. Retrieved 2013-10-15.{{cite web}}: CS1 maint: archived copy as title (link)
  33. ↑ Beresford, H. Richard (July 1996). "Ethics in Neuroscience: Mind over Matter" (PDF). Indiana University. Archived from the original (PDF) on November 1, 2005.
  34. 1 2 3 4 Meinke, Sue (June 1989). "Anencephalic Infants as Potential Organ Sources: Ethical and Legal Issues" (PDF). National Reference Center for Bioethics Literature. Archived (PDF) from the original on 2012-05-22. Retrieved 19 July 2012.
  35. ↑ "The World's Abortion Laws Map 2013 Update" (PDF). Archived (PDF) from the original on 2015-12-02. Retrieved 2015-11-30.
  36. ↑ "Anencephaly in Brazil: A New Decision, Old Issues". Archived from the original on 13 May 2012. Retrieved 19 July 2012.
  37. ↑ Rachels, James. "What is Morality" (PDF). Archived (PDF) from the original on 2014-12-14. Retrieved 19 July 2012.
  38. ↑ "Uniform Declaration of Death Act (UDDA)". Archived from the original on 2013-09-06. Retrieved 2013-08-23.
  39. ↑ Chen, Chih-Ping (2008). "Syndromes, Disorders and Maternal Risk Factors Associated with Neural Tube Defects (III)". Taiwanese Journal of Obstetrics and Gynecology. 47 (2): 131–40. doi: 10.1016/S1028-4559(08)60070-4 . PMID   18603496.
  40. ↑ Zhao, Qi; Behringer, Richard R.; De Crombrugghe, Benoit (1996). "Prenatal folic acid treatment suppresses acrania and meroanencephaly in mice mutant for the Cart1 homeobox gene". Nature Genetics. 13 (3): 275–83. doi:10.1038/ng0796-275. PMID   8673125. S2CID   12341689.
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