Editing Cyclopia (section)

== Causes ==
Genetic defects or toxins can misdirect the embryonic forebrain-dividing process.<ref name="medterms">{{cite web|url=http://www.medterms.com/script/main/art.asp?articlekey=15530|title=Cyclopia definition|work=Medical Dictionary|publisher=MedTerms|access-date=2008-11-29|archive-date=2013-11-02|archive-url=https://web.archive.org/web/20131102213304/http://www.medterms.com/script/main/art.asp?articlekey=15530|url-status=dead}}</ref> One highly [[teratogenic]] alkaloid toxin that can cause cyclopia is [[cyclopamine]] or 2-deoxyjervine, found in the plant ''[[Veratrum californicum]]'' (also known as corn lily or false hellebore). Grazing animals are most likely to ingest this plant and induce cyclopia in offspring. People sometimes accidentally ingest false hellebore while pregnant thinking it is [[hellebore]], which has been suggested as a "natural" treatment for [[vomiting]], [[cramp]]s, and poor circulation – three conditions which may be present in the early stages of pregnancy.<ref>{{cite web|url=http://www.teratology.org/members/JMFpresentation/tsld011.htm|title=Teratology Society|access-date=2007-09-24|archive-url=https://web.archive.org/web/20071218093222/http://www.teratology.org/members/JMFpresentation/tsld011.htm|archive-date=2007-12-18|url-status=dead}}</ref> Cyclopia occurs  when [[Holoprosencephaly#Genetics|certain proteins are inappropriately expressed]],<ref>{{Cite journal|title=Mutations in the C-terminal domain of Sonic Hedgehog cause holoprosencephaly|journal=Human Molecular Genetics|volume=6|issue=11|pages=1847–1853|author1=Erich Roessler |author2=Elena Belloni |author3= Karin Gaudenz |author4= Fernando Vargas |author5=Stephen W. Scherer |author6= Lap-Chee Tsui |author7=Maximilian Muenke |name-list-style=amp |year=1997|doi=10.1093/hmg/6.11.1847|pmid=9302262|doi-access=free}}</ref> causing the brain to stay whole, rather than developing two distinct hemispheres. This leads to the fetus having one [[Midbrain#Corpora quadrigemina|optic lobe]] and one [[Olfactory bulb|olfactory lobe]], resulting in the eye and nose malformations of cyclopia.<ref>{{cite journal|title=Cyclopia and defective axial patterning in mice lacking Sonic hedgehog gene function|journal=Nature|author1=Chin Chiang |author2=Ying Litingtung |author3=Eric Lee |author4=Keith E. Young |author5=Jeffrey L Corden |author6=Heiner Westphal |author7=Philip A. Beachy | doi=10.1038/383407a0 | volume=383 |issue=6599|pmid=8837770 | pages=407–413|year=1996|bibcode=1996Natur.383..407C|s2cid=4339131}}</ref>

The [[Sonic hedgehog protein]] (SHH) is the gene regulator involved in the separation of the single eye field into two bilateral fields.<ref>{{cite book |last= Carlson |first= Bruce |year= 2014 |title= Human Embryology and Developmental Biology |edition = 5th |publisher= Elsevier |page= 309 |isbn= 978-1-4557-2794-0}}</ref> 
Although not proven, it is thought that SHH emitted from the prechordal plate suppresses [[Pax6]], which causes the eye field to divide into two. If the SHH gene is mutated, the result is cyclopia, a single eye in the center of the face (Gilbert, 2000).