ABSENCE OF THE SUPERIOR LABIAL FRENULUM IN HOLOPOSENCEPHALY - A NEW DIAGNOSTIC SIGN

The upper lips of 17 consecutive individuals with various forms of hol oprosencephaly were, examined either at autopsy or during clinical eva luation. A total of 88% of cases were missing the superior labial fren ulum regardless of the severity Of holoprosencephaly or other associat ed craniofacial defects. Because the frenulum was found to be missing across a complete clinical spectrum of holoprosencephaly including cas es exhibiting only minimal craniofacial features, it should be inspect ed as part of the craniofacial examination, and its absence should pro mpt imaging studies of the brain. Absence of the frenulum in holoprose ncephaly also provides evidence that its embryonic origin is that of t he medial nasal process.