Holoprosencephaly

Holoprosencephaly (HPE) is a cephalic disorder in which the prosencephalon (the forebrain of the embryo) fails to develop into two hemispheres, typically occurring between the 18th and 28th day of gestation. Normally, the forebrain is formed and the face begins to develop in the fifth and sixth weeks of human pregnancy. The condition also occurs in other species. Holoprosencephaly is estimated to occur in approximately 1 in every 250 conceptions and most cases are not compatible with life and result in fetal death in utero due to deformities to the skull and brain. However, holoprosencephaly is still estimated to occur in approximately 1 in every 8,000 live births. When the embryo's forebrain does not divide to form bilateral cerebral hemispheres (the left and right halves of the brain), it causes defects in the development of the face and in brain structure and function. The severity of holoprosencephaly is highly variable. In less severe cases, babies are born with normal or near-normal brain development and facial deformities that may affect the eyes, nose, and upper lip. Symptoms of holoprosencephaly range from mild (no facial/organ defects, anosmia, or only a single central incisor) to moderate to severe (cyclopia). The symptoms are dependent upon the classification type. There are four classifications of holoprosencephaly as well as a mild "microform". Alobar Most severe form includes formation of synophthalmia (a single central eye), proboscis, and severe impairment. Semilobar Can present with severely decreased distance between eyes, a flat nasal bridge, eye defects, cleft lip and palate, and severe impairment. Lobar Can present with decreased distance between eyes, a flat nasal bridge, closely spaced nostrils, mental and locomotion delays may be present. Syntelencephaly or middle interhemispheric variant of holoprosencephaly (MIHV) Mild phenotypic presentation which can present with flat nasal bridge, metopic prominence, shallow philtrum, and possible mental and locomotion delays.

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Microcephaly

Microcephaly (from Neo-Latin microcephalia, from Ancient Greek μικρός mikrós "small" and κεφαλή kephalé "head") is a medical condition involving a smaller-than-normal head. Microcephaly may be present at birth or it may develop in the first few years of life. Brain development is often affected; people with this disorder often have an intellectual disability, poor motor function, poor speech, abnormal facial features, seizures and dwarfism.

Birth defect

A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can range from mild to severe. Birth defects are divided into two main types: structural disorders in which problems are seen with the shape of a body part and functional disorders in which problems exist with how a body part works. Functional disorders include metabolic and degenerative disorders.

Retinal axon misrouting at the optic chiasm in mice with neural tube closure defects

Friedrich Beermann

In a new mouse mutant, circletail (Crc), failure of neural tube closure (embryonic day [E] 8-9) is associated with errors in retinal axon projection at the optic chiasm (E12-18), such that many axons normally projecting contralaterally instead grow to ipsi ...

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