“In the second image, holoprosencephaly occurred in one out of every 8,000 births. "However, the most extreme form, cyclopia (a single eye), was much rarer, occurring in only one out of 100,000 ...

An abnormal development of the forebrain, holoprosencephaly, is the most common cranial abnormality in infants with Trisomy 13. The embryology and implications of holoprosencephaly are described.