Acalvaria, holoprosencephaly, and facial dysmorphism syndrome.

An estimated 85-day-old human fetus exhibited a malformation complex consisting of holoprosencephaly, absent calvaria, exophthalmic hypertelorism, and severe bilateral midfacial orofacial clefting involving the maxillary/frontonasal prominences (oblique facial clefts), upper lip (bilateral clefts), and palate (complete cleft). This combination of dysplasias precludes assignment to previously described syndrome complexes. The presence of an olfactory nerve/ethmoidal bone complex does not conform with "classic holoprosencephaly," nor does acalvaria without cerebral dysraphism fit into the cranioschisis and exencephaly syndromes. It is postulated that this combination of anomalies is due to faulty embryogenesis of the prechordal cephalic mesenchyme, leading to failure of telencephalic cleavage and of neural crest-mediated development of the calvaria and facial prominences.