Single mandibular incisor in a patient with del (18p) anomaly.

A single mandibular incisor and an unusually narrow mandible and tongue were noted in an 8-year-old moderately retarded boy with 18p- (45, XY, der dic (18) (18qter-p11.2::22p 11.2-qter). While a single maxillary incisor, considered a minor feature of holoprosencephaly, was reported in three cases of 18p-, reduction of mandibular incisors has been a very rare finding and has never been noted in similar cases.