Mutation of human SHH or its downstream effectors result in a variety of severe developmental disorders; those affecting the head and face include holoprosencephaly, cyclopia and hypotelorism (Belloni et al., 1996; Dubourg et al., 2007; Nanni et al., 1999; Roessler et al., 1996). This evidence concerns the gene SHH and holoprosencephaly.