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What is holoprosencephaly (HPE)?

Holoprosencephaly (HPE), pronounced “hah-low-prah-sen-SEH-fuh-lee,” is a birth defect (congenital condition) that causes a developing baby’s brain to not properly separate into the right and left hemispheres (halves). HPE can also affect the development of an unborn baby’s head and face.

Your brain is normally divided into the left and right hemispheres, but they remain in contact and communication with one another by the corpus callosum (a nerve fiber bundle in your brain). Each hemisphere further divides into the frontalparietaloccipital and temporal lobes.

This division is important for several reasons, including allowing your brain to process several pieces of information and to perform several actions at once. When your brain doesn’t divide properly in development, as in HPE, it causes several physical and neurological issues.

Holoprosencephaly happens very early in fetal development in the womb. There are several different types of holoprosencephaly with a wide range of severity and symptoms. The condition affects each child differently.