Hypomandibular faciocranial dysostosis: report of an affected sib and follow-up.

Hypomandibular faciocranial dysostosis is a condition heretofore described only in a single case. We report the birth of an affected sister along with follow-up information on the initial surviving patient. While a primary error in neural crest development was postulated in this syndrome, subsequently discovered anatomical abnormalities suggest a more complex pathogenesis.