To date, HHAT (Dennis et al., 2012), Disp (Roessler et al., 2009; Kantarci et al., 2010), Cdo (Bae et al., 2011), Gas1 (Pineda-Alvarez et al., 2012), and Gli2 (Roessler et al., 2003) have been reported as causal genes for HPE. Here, GAS1 is linked to holoprosencephaly.