PBO has been found to inhibit the Hedgehog signaling pathway, a critical regulator of brain and face development in all vertebrates, via antagonism of the protein Smoothened (SMO).[16] PBO was found to be capable of causing dose-dependent brain and face malformations in mice exposed during early development, including the rare human birth defect Holoprosencephaly.[17] Even doses of PBO that did not cause overt holoprosencephaly-associated facial abnormalities were found to cause subtle neuroanatomical defects,[18] for which the cognitive or behavioral consequences are unknown.