Triple mutants deficient in the three receptors Gas1, Cdo, and Boc display severe forebrain and cardiovascular defects at e8.5, and later holoprosencephaly, cyclopia, and neural tube pattern defects (Allen et al., 2011), which resemble the Shh/Ihh compound or Smo knockout phenotypes (Zhang et al., 2001b). This evidence concerns the gene GAS1 and holoprosencephaly.