Holoprosencephaly (HPE) is a complex brain malformation resulting from incomplete cleavage of the prosencephalon, occurring between the 18th and 28th day of gestation, and affecting both the forebrain and face, which results in neurological manifestations and facial anomalies of variable severity. The disease is Monarch Disease Ontology term MONDO_0016296 (holoprosencephaly). Also known as: HPE, holoprosencephaly sequence.