All Wnt5a-/-;LtapLp/+ mutants exhibited craniorachischisis, indicating a drastic increase in penetrance as compared to the craniorachischisis phenotype displayed by Wnt5a-/- (1 in 34) or LtapLp/+ animals (0 in more than 100) [98]. The gene discussed is WNT5A; the disease is craniorachischisis.