CDON and holoprosencephaly: A positive role for Cdon is revealed in Cdon KO mice, which exhibit a range of phenotypes consistent with absent or impaired Shh signaling, including holoprosencephaly (HPE) and Septo Optic Dysplasia (SOD) (Bae et al., 2011; Cavodeassi et al., 2019; Kahn et al., 2017; Zhao et al., 2012).