Children's Hospital Colorado
Colorado Fetal Care Center


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What is holoprosencephaly (HPE)?

Holoprosencephaly (HPE) is a brain condition in which the two halves of a baby’s brain do not fully separate, as they normally would, while they develop in the womb. The brain is made of two halves, or hemispheres, that are mirror images of each other. If they do not fully separate during development, your baby will receive an HPE diagnosis.

HPE can cause several issues, including:

  • Developmental delays
  • Facial structure differences, such as eyes that are spaced close together, nasal issues and cleft lip and cleft palate
  • Fluid cysts and hydrocephalus (buildup of fluid pressure) in the brain
  • Growth problems
  • Vision problems

Different forms of holoprosencephaly

We diagnose HPE depending on how separated the two brain halves are:

Lobar holoprosencephaly

Lobar HPE is the least severe form of holoprosencephaly. The brain’s halves are mostly separated, only connected in the frontal lobe (the front-most part of the brain). In lobar HPE, the corpus callosum, which allows the two halves of the brain to communicate, is mostly (but not completely) formed.

Semi-lobar holoprosencephaly

Semi-lobar HPE is in between the least and most severe form of holoprosencephaly. The halves are mostly connected but separated slightly at the back of the brain.

Alobar holoprosencephaly

Alobar HPE is the most severe form of holoprosencephaly. The brain’s halves are completely connected or fused together.

What causes holoprosencephaly?

HPE usually occurs due to a genetic difference in the child, which impacts how the brain develops. Sometimes parents pass genetic differences to their kids and sometimes they are new in the child. There are certain genetic syndromes, such as Trisomy 13, that we often link to HPE.

HPE can also occur because a baby has missing or copied sections of chromosomes (the structure inside cells that contain all our genes). In this case, the child has what is called a micro-deletion syndrome or duplication syndrome. Missing or copied chromosomes can impact a child’s development and the function of other parts of the body, as well.

There are also a handful of single-gene changes that can cause HPE, meaning that a gene within a chromosome has been altered in some way. Some of single-gene changes can cause HPE but don’t cause symptoms in everyone who has them, so a parent can have the same change and not have symptoms of HPE.

Who gets holoprosencephaly?

HPE begins very early in pregnancy. We have not seen signs of the condition to be more common in specific genders or races.

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