Single maxillary incisor in a child with holoprosencephaly

Holoprosencephaly is a congenital abnormality in which the prosencephalon (embryonic forebrain) fails to develop into two discrete hemispheres. It is commonly associated with midfacial defects. Holoprosencephaly represents a spectrum of craniofacial and central nervous system defects; the severity of the facial defects generally correlates with the severity of the CNS abnormalities. The mildest form can have a subtle presentation in which the only apparent physical finding is a single central maxillary incisor (arrow).