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Midline interhemispheric variant of holoprosencephaly

Synonym(s) MIH
MIH type HPE
Middle interhemispheric fusion variant
Middle interhemispheric variant of holoprosencephaly
Prevalence 1-9 / 100 000
Inheritance Multigenic/multifactorial
or Not applicable
Age of onset Infancy
  • Q04.2
MeSH -
MedDRA -


Disease definition

Midline interhemispheric variant of holoprosencephaly (MIH) or syntelencephaly is a form of holoprosencephaly (HPE; see this term) characterized by non-separation of the posterior frontal and parietal lobes, normally-formed callosal genu and splenium, absence of the callosal body, normally-separated hypothalamus and lentiform nucleus, and frequent heterotopic gray matter.


About 2% to 15% of HPE patients have MIH type.

Clinical description

Patients have rather mild dysmorphic facial features such as ocular hypotelorism, flat or narrow nasal bridge or a relatively normal facial appearance.


MIH has mainly been reported in patients with ZIC2 (13q32) mutations.


Prognosis is better than in classical forms of HPE.

Expert reviewer(s)

  • Dr Sandra MERCIER
  • Pr Sylvie ODENT

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Detailed information

Summary information
Clinical genetics review
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