Other gene mutations that induce HPE and result in HH pathway dysregulation involve PTCH, Growth arrest-specific 1 (GAS1), CDO, and BOC (Roessler and Muenke, 1998; Seppala et al., 2007; Allen et al., 2011; Bae et al., 2011; Zhang et al., 2012). Here, GAS1 is linked to holoprosencephaly.