The forebrain normally develops around fifth or sixth week of pregnancy. In cases of Holoprosencephaly, the forebrain fails to divide into bilateral hemispheres. This results in defects of the brain, as well as facial malformations.
Holoprosencephaly falls into three classes:
1. Alobar Holoproencephaly is when the brain does not divided at all. This is usually associated with severe facial deformities.
2. Semilobar Holoprosencephaly is when the brain’s hemispheres have somewhat divided, causes an intermediate form of the disorder.
3. Lobar Holoprosencephaly is when there is more separation between brain hemispheres. This is the least severe form, and the fetal brain may be nearly normal.
According to the National Institute of Neurological Disorders and Stroke (NINDS), “in most cases of holoprosencephaly, the malformations are so severe that babies die before birth.”
The prognosis depends on the degree of fusion between brain hemispheres, the malformation of the brain, and other health issues the fetus may have. The more severe cases are often fatal. Holoprosencephaly may present with of a spectrum of other malformations and abnormalities. Moderate to severe defects may cause mental retardation, spastic quadriparesis, athetoid movements, endocrine disorders, epilepsy and other serious conditions; mild brain defects may only cause learning or behavioral problems and possibly mild motor impairments.
For more information on Holoprosencephaly, visit:
- NINDS – Holoprosencephaly Information Page
- NORD – Holoprosencephaly Abstract
- NCBI – Holoprosencephaly Overview