Alobar holoprosencephaly
Small single forebrain ventricle
No interhemispheric division
Absence of olfactory bulbs and tracts
Absence of corpus callosum
Non separation of deep gray nuclei
Semilobar holoprosencephaly
Rudimentary cerebral lobes
Incomplete interhemispheric division
Absence or hypoplasia of olfactory bulbs and tracts
Absence of corpus callosum
Varying non separation of deep gray nuclei
Lobar holoprosencephaly
Fully-developed cerebral lobes
Distinct interhemispheric division
Midline continuous frontal neocortex
Absent, hypoplasic or normal corpus callosum
Separation of deep gray nuclei
Syntelencephaly, or middle interhemispheric variant of holoprosencephaly (MIHV)
Failure of separation of the posterior frontal and parietal lobes
Callosal genu and splenium normally formed
Absence of corpus callosum
Hypothalamus and lentiform nuclei normally separated
Heterotopic gray matter
Microform
Subtle defects of corpus callosum
Subtle midline brain defects

Causes
In Holoprosencephaly, the neural tube fails to segment, resulting in incomplete separation of the prosencephalon at the fifth week of gestation.The exact cause(s) of HPE are yet to be determined. Mutations in the gene encoding the SHH protein, which is involved in the development of the central nervous system (CNS), can cause holoprosencephaly. In other cases, it often seems that there is no specific cause at all. Genetics
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 recognizable 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).
Keratosis pilaris atropicans includes many forms of keratosis pilaris with cicatricial alopecia. : 762   Variants include keratosis pilaris atrophicans faciei, atrophoderma vermiculatum, keratosis follicularis spinulosa decalvans, and ichthyosis follicularis. : 762

See also
Cicatricial alopecia
List of cutaneous conditions


== References ==