Exencephaly
Encyclopedia
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.
The prognosis for infants born with exencephaly is extremely poor. It is rare to find an infant born with exencephaly, as most cases that are not early stages of anencephaly are usually stillborn
. Those infants who are born with the condition usually die within hours or minutes.
s, 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. Exencephaly is one such disease that has recently been identified as part of an emerging
class of diseases called cilopathies
. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell
, organelle
s which are 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
.
Cephalic disorder
Cephalic disorders are congenital conditions that stem from damage to, or abnormal development of, the budding nervous system...
wherein the brain is located outside of the skull. This condition is usually found in embryos as an early stage of anencephaly
Anencephaly
Anencephaly is a cephalic disorder that results from a neural tube defect that occurs when the cephalic end of the neural tube fails to close, usually between the 23rd and 26th day of pregnancy, resulting in the absence of a major portion of the brain, skull, and scalp...
. As an exencephalic pregnancy progresses, the neural tissue gradually degenerates.
The prognosis for infants born with exencephaly is extremely poor. It is rare to find an infant born with exencephaly, as most cases that are not early stages of anencephaly are usually stillborn
Stillbirth
A stillbirth occurs when a fetus has died in the uterus. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than . Once the fetus has died the mother still has contractions and remains undelivered. The term is often used in...
. Those infants who are born with the condition usually die within hours or minutes.
Relation to other rare disorders: genetic ciliopathy
Until recently, the medical literature did not indicate a connection among many genetic disorderGenetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
s, both genetic syndromes
Syndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
and genetic diseases
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
, 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
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
despite the widely-varying set of medical symptoms
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
that are clinically visible in the disorders. Exencephaly is one such disease that has recently been identified as part of an emerging
Emergence
In philosophy, systems theory, science, and art, emergence is the way complex systems and patterns arise out of a multiplicity of relatively simple interactions. Emergence is central to the theories of integrative levels and of complex systems....
class of diseases called cilopathies
Ciliopathy
A ciliopathy is a genetic disorder of the cellular cilia or the cilia anchoring structures, the basal bodies, or of ciliary function.Although ciliopathies are usually considered to involve proteins that localize to the primary cilia or centrosomes, it is possible for ciliopathies to be associated...
. The underlying cause may be a dysfunctional molecular mechanism in the primary cilia structures of the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
s which are present in many cellular types throughout the human
Human
Humans are the only living species in the Homo genus...
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
Primary ciliary dyskinesia
Primary ciliary dyskinesia , also known as immotile ciliary syndrome or Kartagener Syndrome ', is a rare, ciliopathic, autosomal recessive genetic disorder that causes a defect in the action of the cilia lining the respiratory tract and fallopian tube, and also of the flagella of sperm in...
, Bardet–Biedl syndrome, polycystic kidney
Polycystic kidney disease
Autosomal dominant polycystic kidney disease is an inherited systemic disorder that predominantly affects the kidneys, but may affect other organs including the liver, pancreas, brain, and arterial blood vessels...
and liver disease
Polycystic liver disease
Polycystic liver disease usually describes the presence of multiple cysts scattered throughout normal liver tissue, in association with polycystic kidney disease.-Pathophysiology:Associations with PRKCSH and SEC63 have been described....
, nephronophthisis
Nephronophthisis
Nephronophthisis is a genetic disorder of the kidneys which affects children. It is classified as a medullary cystic kidney disease.The disorder is inherited in an autosomal recessive fashion and, although rare, is the most common genetic cause of childhood kidney failure.It is a form of...
, Alström syndrome
Alstrom syndrome
Alström syndrome is a rare genetic disorder caused by mutations in the gene ALMS1. It is among the rarest genetic disorders in the world, as currently it has only 266 reported cases in medical literature and over 501 known cases in 47 countries. It was first described by Carl-Henry Alström in...
, Meckel–Gruber syndrome and some forms of retinal degeneration
Retinopathy
Retinopathy is a general term that refers to some form of non-inflammatory damage to the retina of the eye. Frequently, retinopathy is an ocular manifestation of systemic disease.-Pathophysiology:Causes of retinopathy are varied:...
.