Impaired function of BOC, CDON, and GAS1 appears to underlie holoprosencephaly, both in humans (Clement et al. 2007; Ribeiro et al. 2010; Pineda-Alvarez et al. 2012; Bae et al. 2011) and in mice (Seppala et al. 2007; Zhang et al. 2006; McLellan et al. 2008). Here, CDON is linked to holoprosencephaly.