Structures Alobar HPE Semi-lobar HPE Lobar HPE Microform HPE Ventral IHS Absent Absent Absent Asymptomatic form without neuro-anatomic anomalies. Submicroscopic anomalies with haploinsuffiency of gene Dorsal IHS Absent Partial Present Olfactiv tract Absent/single Absents/Present/Single Absent/Present Optic Nerve Present/single Present/Single Present Ventricles Single Single Single Corpus callosus Absent Absent Absent Thalami Single Single Single

Table 2: HPE classification. IHS: interhemispheric sulcus. HPE: holoprosencephaly.