Holoprosencephaly
You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.
| Holoprosencephaly Classification and external resources | |
 | |
|---|---|
| Diagram depicting the main subdivisions of the embryonic vertebrate brain. | |
| ICD-10 | Q04.2 |
| ICD-9 | 742.2 |
| OMIM | 236100 |
| DiseasesDB | 29610 |
| eMedicine | radio/347 |
| MeSH | D016142 |
Holoprosencephaly is a type of cephalic disorder. This is a disorder characterized by the failure of the prosencephalon (the forebrain of the embryo) to develop. During normal development the forebrain is formed and the face begins to develop in the fifth and sixth weeks of human pregnancy. (The condition also occurs in other species, as with Cy, the Cyclops kitten.) Holoprosencephaly is caused by a failure of the embryo's forebrain to divide to form bilateral cerebral hemispheres (the left and right halves of the brain), causing defects in the development of the face and in brain structure and function.
Symptoms
Symptoms of holoprosencephaly range from mild (anosmia, or a single central incisor) to moderate (cleft lip or palate) to severe (synophthalmia proboscis or cyclopia).
There are three classifications of holoprosencephaly.
- Alobar holoprosencephaly, the most serious form in which the brain fails to separate, is usually associated with severe facial anomalies.
- Semilobar holoprosencephaly, in which the brain's hemispheres have a slight tendency to separate, is an intermediate form of the disease.
- Lobar holoprosencephaly, in which there is considerable evidence of separate brain hemispheres, is the least severe form. In some cases of lobar holoprosencephaly, the patient's brain may be nearly normal.
Presentation
Holoprosencephaly, once called arhinencephaly, consists of a spectrum of defects or malformations of the brain and face. At the most severe end of this spectrum are cases involving serious malformations of the brain, malformations so severe that they often cause miscarriage or stillbirth. At the other end of the spectrum are individuals with facial defects - which may affect the eyes, nose, and upper lip - and normal or near-normal brain development. Seizures and mental retardation may occur.
The most severe of the facial defects (or anomalies) is cyclopia, an abnormality characterized by the development of a single eye, located in the area normally occupied by the root of the nose, and a missing nose or a nose in the form of a proboscis (a tubular appendage) located above the eye. The condition is also referred to as cyclocephaly or synophthalmia and is very rare.
Causes
In his book Mutants: On the Form, Varieties and Errors of the Human Body [1], Armand Marie Leroi describes the cause of cyclopia as a genetic malfunctioning during the process by which the embryonic brain is divided into two. Only later does the visual cortex take recognisable form, and at this point an individual with a single forebrain region will be likely to have a single, possibly rather large, eye (at such a time, individuals with separate cerebral hemispheres would form two eyes).
Increases in expression of such genes as Pax-2, as well as inhibition of Pax-6, from the notochord have been implicated in normal differentiation of cephalic midline structures. Inappropriate expression of any of these genes may result in mild to severe forms of holoprosencephaly.
Incidence/prevalence
Leroi goes on to state that:
- [Holoprosencephaly] is, in all its manifestations, the most common brain deformity in humans, afflicting 1 in 16,000 live-born children and 1 in 200 miscarried fetuses.
Prognosis
The more severe forms of holoprosencephaly are usually fatal. People born with the mildest form (only one incisor) may have mild to moderate developmental delay and pituitary dysfunction.[1]
Recent events
On 11 January 2006, Associated Press and other news organisations published photographs of a kitten that was born in Oregon, United States with cyclopia. The kitten's owner expressed surprise at having witnessed such a thing, with some bloggers on the internet expressing disbelief over the authenticity of the photographs published[1].
References
External links
See also
Congenital malformations and deformations of nervous system (Q00-Q07, 740-742) | |
|---|---|
| Brain | Anencephaly (Acephaly, Acrania, Iniencephaly) - Encephalocele - Microcephaly - Congenital hydrocephalus (Dandy-Walker syndrome) - other reduction deformities (Holoprosencephaly, Lissencephaly, Pachygyria, Hydranencephaly) - Septo-optic dysplasia - Megalencephaly - Congenital cerebral cysts (Porencephaly, Schizencephaly) - Congenital brain tumors |
| Brain stem | Arnold-Chiari malformation |
| Spinal cord | Spina bifida - Currarino syndrome - Sacrococcygeal teratoma - Diastematomyelia - Syringomyelia |
| see also non-congenital CNS and PNS (G, 320-359) | |
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
