Cyclopia is a rare form of holoprosencephaly. The synonyms for Cyclopia are cyclocephaly or synophthalmia.
Cyclopia is a congenital birth defect and a rare one,occurring in an incidence of 1 in 200 miscarriages. Cyclopia is not confined only to the human species but may occur in animals too (1 in 16,000 born animals).
The baby usually has one eye (commonly called as One-eyed baby) located in the forehead at the site of what should have been the root of the nose. There’s a missing nose or a small non-functional nose called Proboscis (a tubular appendage) present above the eye on the forehead or on the back . Most such embryos get naturally aborted or are stillborn upo
Genetic causes or toxins can misdirect the embryonic forebrain dividing process. One such alkaloid toxin thought to be responsible is Cyclopamine, found in the plant Veratrum californicum (false hellebore).
Humans may ingest this plant by mistake considering it as hellebore which is an unrelated plant and recommended as a natural treatment for vomiting,cramps and poor circulation quite common in the early months of pregnancy .
Certain proteins are inappropriately expressed causing the brain to stay whole rather than dividing into two separate hemispheres. This leads to the foetus having one optic lobe and one olfactory lobe resulting in the typical malformations of Cyclopia.
Genetic basis –
The sonic hedgehog (SHH) gene regulator is involved in the separation of the single eye field into two bilateral fields. Mutation of the SHH gene results in Cyclopia, a single eye in the center of the face .
Holoprosencephaly is a cephalic disorder in which the prosencephalon (the part from which the forebrain develops) fails to completely separate into two hemispheres. Normally the forebrain develops and the face also begins to form around the fifth and sixth weeks of human pregnancy. If the embryo’s forebrain fails to divide to form bilateral cerebral hemispheres (the left and right halves of the brain), it results in defects in the development of the face and in brain structure and function. In very severe cases of prosencephaly , the malformations turn out to be so serious that the babies usually die before birth . However in less severe cases,the baby may be born with almost normal brain development but there are defects in the development of face i.e., eyes,nose or lip.
Some cases of Cyclopia have been found in farm animals such as horses, sheep, pigs and even in some chickens. In such cases, the nose and the mouth fail to form or the nose grows from the roof of the mouth causing obstruction to the airflow after birth.