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, though the condition also occurs in other species (as with Cy, the Cyclops Kitty). 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. more...
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.
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 are incompatible with life and often cause spontaneous intrauterine death. 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.
In his book Mutants: On the Form, Varieties and Errors of the Human Body , 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).
Leroi goes on to state that:
- 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 foetuses.
The regular appearance in Western society of such deformed human babies seems to have ceased or been withheld from the public view, probably in part due to the contemporary Western practice of hospitalisation at birth.
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.
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