What is Holoprosencephaly?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 04 June 2019
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Holoprosencephaly (HPE) is a congenital birth defect in which the brain fails to develop properly. The vast majority of fetuses with holoprosencephaly spontaneously abort, with around one to two in 10,000 surviving to birth. The severity of this birth defect can be quite varied. Some individuals are so severely afflicted that they die shortly after birth, while others may be relatively normal, with development comparable to that of other infants.

This condition has a genetic component, and it also appears to be influenced by infections and the use of drugs in early pregnancy. Diabetic women are also more at more risk of having children with holoprosencephaly, especially if their blood sugar is not well controlled. Because brain development starts occurring very early, the conditions which can lead to holoprosencephaly must be present shortly after conception.

In fetuses with holoprosencephaly, the embryonic forebrain fails to develop completely, and it does not separate into two lobes. In alobar forms of this condition, there is no differentiation at all between the lobes. This form is usually fatal. Other forms include semilobar and lobar, along with the middle hemispheric variant, in which the middle of the brain is not fully differentiated. The issues with brain development can often be identified on an ultrasound.


In addition to causing defects in the brain, holoprosencephaly also causes facial and skull deformities. In mild cases, the face may be minimally affected, but conditions like cleft lips and palates are not uncommon. More severe deformities include a small or misshapen skull, a missing or severely malformed nose, or cyclopia, in which a single eye forms in the middle of the forehead.

If the diagnosis has been missed during prenatal care, the condition is usually evident at birth, due to the facial deformities which appear in most cases. Various diagnostic tools can be used to confirm that the infant has holoprosencephaly.

Infants born with survivable forms of this condition can experience developmental delays, seizures, and apnea. This condition is not progressive, which means that additional damage will not occur after birth, and in children with more mild forms, it is possible to reach a high degree of intellectual development and independence. Children with this condition will need focused therapy and attention, with parents who will act as advocates to get the care that they need. Surgery may also be recommended to correct facial abnormalities so that the child will feel more comfortable in society.



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