Mondo Description Midline interhemispheric variant of holoprosencephaly (MIH) or syntelencephaly is a form of holoprosencephaly (HPE) 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.