Absence of the superior labial frenulum in holoprosencephaly: a new diagnostic sign.

The upper lip of 17 consecutive individuals with various forms of holoprosencephaly were examined either at autopsy or during clinical evaluation. A total of 88% of cases were missing the superior labial frenulum regardless of the severity of holoprosencephaly or other associated craniofacial defects. Because the frenulum was found to be missing across a complete clinical spectrum of holoprosencephaly including cases exhibiting only minimal craniofacial features, it should be inspected as part of the craniofacial examination, and its absence should be prompt imaging studies of the brain. Absence of the frenulum in holoprosencephaly also provides evidence that its embryonic origin is that of the medial nasal process.