Holoprosencephaly (HPE) is an uncommon and clinically severe abnormality of forebrain development, resulting from failure of septation, or cleavage, of the midline forebrain structures. It encompasses a range of brain pathology classified as lobar, semilobar or alobar HPE reflecting increasing degrees of failed septation. The closely related development of the mid-face area is frequently disturbed, with coexisting facial phenotypes ranging from cyclopia to normal.